Intro Inorganic Chem
Intro Inorganic Chem CHM 218
Popular in Course
Popular in Chemistry
This 0 page Class Notes was uploaded by Ms. Jayde Murray on Sunday November 1, 2015. The Class Notes belongs to CHM 218 at Indiana University Purdue University - Fort Wayne taught by R. Berger in Fall. Since its upload, it has received 44 views. For similar materials see /class/233559/chm-218-indiana-university-purdue-university-fort-wayne in Chemistry at Indiana University Purdue University - Fort Wayne.
Reviews for Intro Inorganic Chem
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 11/01/15
21 Chapter 2 An Overview of the Periodic Table The Periodic Table Period In 1869 Dmitri Mendeleev a Russian chemist and J Lothar Meyer a German chemist independently discovered that when elements were arranged in horizontal rows in order of increasing atomic weight the rows could be stacked in such a way that elements in the same column had similar chemical properties With a few exceptions this is the same order as in the modem periodic table The modem periodic table is ordered by increasing atomic number rather than increasing atomic weight MainGroup Elements r E 1 2 3 4 5 57 5 Ba La 57527 555555 55 55 7 AB R a 22s 227 MainGroup Elements Atomic number Symbol Atomic weight Metals 45 cu m 2411 mm 72 75 77 Hr Ta Re lr 17s 45 ND 5475 55m 52 217 M m5 m7 Rf on So an 252 262 Mt 25a nner Transition Metals Metal 5s 55 EU a 52 55 54 55 as 57 55 55 7o 71 Lamhanides Ce Pr Nu Pm Sm Eu Gd Tn Dy Ho Er Tm vn Lu 45 115 45 55755 4424 45 55 55 51555 57 25 15s 52554 52 55 54 55552 57 25 5555421 75 54 74557 Metallold Bu 5 52 55 54 55 55 57 55 55 mu 1m m2 m5 quotAdinides Th Pa U N Pu Am Cm ax or E5 Fm Md No Lr 252 5551 251 55555 23s 5255 257 244 252 247 247 251 252 257 255 255 252 Nonmetal A period is a horizontal row in the periodic table while a group or family consists of the elements in a given column 22 Groups 12 and 1318 the A groups are referred to as main group or representative elements while groups 311 are the transition metals Transition metals are those elements that have a partially lled d subshell in the neutral atom or any common oxidation state Your text omits group 3 because the chemistry of these elements more closely resembles that of the lanthanoids The two rows at the very bottom of the chart lanthanoids and actinoids are referred to as the inner transition metals Elements in group 12 are not classi ed as transitions metals either Some families are given speci c names The elements in group 1 with the exception of hydrogen are the allmli metals Elements in group 2 are the alkaline earths Elements in group 15 are the pnictogens 16 are the chalcogens 17 are the halogens and those in group 18 are the noble gases Stability of the Elements From Coulomb s Law we know that like charges repel each other quite strongly at short distances In addition to this repulsion however there is an extremely short range attractive force between nucleons This attractive force is called the nuclear force and is much stronger than the Coulombic repulsions but acts only at very short distances 103915 m Beyond distances corresponding to nuclear dimensions the nuclear force is negligible According to the shell model of the nucleus the protons and neutrons in the nucleus occupy energy levels analogous to the energy levels occupied by electrons outside the nucleus of an atom Just as certain closed shell electron con gurations are associated with the special stability of the noble gases nuclei with certain numbers of neutrons and protons are especially stable These numbers are referred to as magic numbers and correspond to the number of protons or neutrons in a completed shell For protons magic numbers are 2 8 20 28 50 82 and possibly 114 Magic numbers for neutrons are 2 8 20 28 50 82 and 126 There is also evidence that pairs of protons or neutrons impart stability to a given nucleus As indicated in the following table the majority of stable nuclei have an even number of protons and neutrons while a smaller number have either an even number of protons or neutrons but not both A very small number of stable nuclei have an odd number of protons and neutrons Number of Stable Isotopes 157 52 50 5 Number of protons even even odd odd Number of neutrons even odd even odd Another important factor in determining whether a nucleus is stable or not in the neutron to proton ratio For stable nuclei of low atomic number up to 20 the neutron to proton ratio is approximately 1 to l 1 However as the atomic number increases so does the neutron to proton ratio for stable nuclei For nuclei with higher Z more neutrons are required to offset the increasing repulsive interactions among the protons When Z becomes very large no stable nuclei exist Note that no stable nuclei with Z gt 83 exist and all elements with Z 83 with the exception of Tc Z 43 and Pm Z 61 have at least one stable isotope Thorium Th Z 90 and Uranium U Z 92 have no stable isotopes however they are very common because of the extremely long halflives 108 to 109 years of some of their isotopes Number of neutrons N 23 130 Alpha emission 110 F Beta emission Band of 0 102030 405060 70 80 90100 Number of protons Z A plot of the number of neutrons N vs atomic number Z for stable nuclei shows that these stable nuclei fall in a narrow band referred to as the band of stability Classi cation of the Elements The elements can be classi ed with respect to a number of diiTerent characteristics 1 Phase at Standard Ambient Temperature and Pressure SATP 25 C and 100 kPa Under these conditions two elements are liquid 11 are gases and the rest are solids 2 MetalNonmetal We must carefully de ne our metalnonmetal criteria Metals typically have a characteristic luster 7 However some nonmetals such as iodine and metalloids such as silicon also have lustrous surfaces Metals tend to be good conductors of heat7 However diamond an allotrope of the nonmetal carbon has an extremely high thermal conductivity 24 Metals are usually malleable anal ductile 7 However some of the transition metals are very brittle High three dimensional electrical conductivity at SATP is likely the best criterion of a metal We specify 3D because graphite another allotrope of carbon has a high electrical conductivity in two dimensions due to its layered structure We specify 25 C because below 18 C tin exists in the gray tin form which is a semiconductor and 100 kPa because at elevated pressure iodine becomes a conductor Furthermore the conductivity of a metal decreases with increasing temperature whereas the conductivity of nonmetals increases under these conditions The metalloids or semimetals B Si Ge As Te exhibit behavior which is intermediate between metals and nonmetals Periodic Properties Many properties of the elements can be understood in terms of the electron con gurations of their atoms As we mentioned previously atoms of elements in the same group or family have the same valence shell electron con guration Since valence shell con guration in uences chemical reactivity elements in the same family will exhibit similar chemical properties Periodic Law states that when the elements are arranged in order of increasing atomic number their chemical and physical properties vary periodically These properties are therefore called periodic properties and we will consider three of them atomic radius ionization energy and electron affmity The latter two are of particular importance in the subject of chemical bonding 1 Atnmm Radms rm mdms is a snmswhat arnbxgunus pmperty K L d Y L the nucleus but dnesnntabmpdy reach zem As a quot m e d ssvml measures nf amme mdxus exist A Cnvalentradms HalthednsLancebetwemLhenuda nf Wm xdmncal amms when jnmed by a 3 Few smglebnnd Ynu sham recall um an angska A is aumt nf measure equaltn 10 m 100m 2128A064A F2 01128A rum B VanderWazlsmdxus Halfmemsmncebemeenmenudanftwnaznmsnfamacem mm as lecul n e lvdwa c MPHM r In 26 Fairly reliable values of covalent radii are tabulated for most of the elements but these are experimental values so there may be variations from one set of measurements to another Two generalizations can be made regarding the variation in covalent radius with position in the periodic chart 1 Covalent radii tend to decrease from le to right across a given period 2 Covalent radii tend to increase from top to bottom in a given family Atomic radius pm 2 10 18 36 54 86 Atomic number 27 A m um WA VA le we mun He a o a a o aquot o J a PM 0 0 090900 090099 remaeeeoooe Pulae 0 eeee ofanatom Tn n rl m m determmes the slze othe atom l The elfeeuve nuelear charge aeung on the eleeuons m the orbltal general the out t eleeuons expmence a posmve charge that ls somewhat smaller han the actual nuelear eharge Thls ls the result of smeemngquot of nuelear eharge by mner eleeuons charge zd ls equal to the actual nuelear eharge Z mmus some sereemng fanor 0 to whleh all the mtervemng eleeuons conmbute Thlslncludes eleeuons m the same shell z ze 0 2 The pnnelpal quantum number n ofthe orbltal Ihelargerlhevalue ofn helargerhe orbltal Thlsls apparentlfyou eonslderlhe eleeuon dasmbunon forlhe argon atom shown above The first factor is of more importance in determining the trend within a given period where n remains 28 constant As each successive electron is added to the valence shell on moving from one element to the next a proton is also added to the nucleus Electrons within the same shell are not perfectly effective in screening or shielding and so the effective nuclear charge increases across a period Li The second factor in more important in determining the radius trend in a given family because the effective nuclear charge remains essentially constant in a given family Li Na K Rb Cs He 2s1 He 2s2 He 2s2 2p1 He 2s2 2p2 He 2s2 2p3 He 2s2 2p4 He 2s2 2p5 2s1 3s1 4s1 5s1 6s1 134A 154A 196A 216A 235 A 134 A 091 A 082 A 077 A 074 A 070 A 068 A Slater39s Rules Wnte me elector stxucmre ofthe atommu m are followmg goupmgs 15 25v 21gt 3539 301 4549 46 40 5559 To calculate ofor angm e39 e39 m groups to me n31 do not sheldthose to me le for us andnp e39 e39 m are same us up goup conmbute 0 351o 0 except m 1s where 0 3015 used e39 m are rr 1 goup conmbute 0 85 e39 m are rr2 andlower groups conmbute 1 00 1 e they shxeld completely forndornfe39 e39 m are same goup conmbute 0 351o 0 e39 m groups to the m conmbute 1 00 Consrder a4d e39 m zr 152 252 21gt 352 3p 301 452 4p 4012 4 552 5pquot 0035361003635 z z 040 36 353 65 Consrder a 5s e39 m zr 00 35100 852810036 85 0403685315 Z1 210 Removal of e39 from an atom reduces the effects of shielding making the ion more Hlike Principle quantum number becomes a more dominant effect in determining energy Ionization Energy Ionization energy is de ned as the minimum energy required to remove the highest energy electron from an isolated neutral gas phase atom For Li the ionization energy is the energy associated with the process Li a L e39 IE 520 kJ 1s2 2s1 a 1s2 Two generalizations can be made regarding the variation in ionization energy IE with position in the periodic chart 1 IE generally decreases from the top of a group to the bottom As r1 increases the electron to be removed is farther away from the nucleus and less tightly bound As a result IE decreases 2 IE generally increases from le to right across a given period although this is not a smooth trend Just as it is responsible for the decrease in atomic radius going across a given period the increasing effective nuclear charge is also responsible for the general increase in IE These trends are illustrated in the accompanying plot of IE vs atomic number As you can see there are some glitches in the variation in IE across a period 2000 1500 1000 Ionization energy kJmol Li Be 36 LE kJmol 520 899 801 1086 1402 1314 1681 2081 Atomic number 212 You will note that in the second period the IE of B is actually smaller than that of Be and that in period three the IE of Al is smaller than that of Mg B and Al have a ns2 np1 valence shell con guration while Be and Mg have a ns2 valence shell con guration In general binding energies for p orbitals are generally smaller than for s orbitals because of the slight shielding effect s e39 have on p e39 Less energy is require therefore to remove the np electron from B or Al than an s electron from Be or Mg In the same two periods 0 and S have smaller IEs than N and P respectively This is due to the fact that O and S have ns2 np4 con gurations in which two electrons occupy the same p orbital whereas N and P have ns2 np3 con gurations and each electron resides in its own orbital The electronelectron repulsion of the two electrons in the same orbital in O and S makes it easier to remove one of them than it would be if they occupied separate orbitals IEs of transition metals gradually increase due to the relatively ineffective shielding of s e39 by d e39 Electrons can be removed successively from atom so atoms have a second ionization energy a third ionization energy etc As each electron is removed an ion with a greater positive charge remains In addition the orbitals containing the remaining electrons contract As a result the value of each successive ionization energy becomes larger Consider the atoms Li Be and B 1131 1132 113 1134 kJmol Li 520 7298 11815 Be 899 1757 14848 21006 B 801 2427 3 660 2 5025 The removal of electrons from a core shell requires large amounts of energies The second ionization energy of Li corresponds to the removal of one of the ls electrons and is more than a factor of 10 greater than the first ionization energy Large increases can also be seen in the third and fourth ionization energies of Be and B respectively Electron Attachment Enthalpy AHEA The property which your text refers to as electron affinity of an atom is actually the electron attachment enthalpy The electron attachment enthalpy is the enthalpy change for the process of adding an electron to a neutral atom in the gas phase to form a negative ion F g e39 a F39 g AHEA 328 ldmol IfAHEA lt 0 energy is released in the process and the formation of a negative ion is energetically favorable If AHEA gt 0 the formation of a negative ion is not energetically favorable The periodic variation in AHEA is somewhat more complicated than atomic radius or ionization energy However AHEA tends to become more negative as you move from le to right across a period AHEA kJmol Li 60 Be 240 1 if 7 if e39 goes into 2p subshell 2s 2p B 27 C l22 N 0 i e39hastopairup 2s 2p 0 l 41 F 328 Ne 30 i 1 JL i e39 goes into n 3 lell 2s 2p Note that the formation of Li39 is exothennic while the formation of Lil is endothermic Sequential electron attachment enthalpies 0 g e39 a 039 g AHEA 141 ldmol 039 g e39 a 0239 g AHEA 744 ldmol This may seem surprising and points out that the oxide ion is stable only in the presence of some other driving force such as the formation of a crystal lattice where the additional energy required can be made up for Chapter 15 e The Gruup 15 Elements Group 15 eonslsts of two very dlsslmllarnonrmetals N anol P a semlrmetal As anol two weak metals Sb andBl N and are both eleetrreally nonrconducnng andhave atrdre oxldes anol are therefore classl ed as nonrmetals As has allotropes that have metalhe anol nonrmetalh appearanee anol forms an amphotene omole Sb andBl form an amphotene anol basl omole respeetvely The oleerease tn m p wrth lnereaslng z anol the long llquld range parallel those of othermatn goup metals Annmalmls Nature or N39m39ngen rp from stolehlometry The NNmple bondls abnormally strong whlle the NrN slngle bond ls ally weak As aresultN orms the dratomle moleeule N2 rather than catmanng as c echonolstrength N2H4Cg01 9 Nng 2H20 C2H4C2301 9 2C02Cg 2H20 Unhke Group 14m Groups 15 anol lo the seeonolelementm the famlly P anol srespeetwely has the greater propenslty to eatenanon 3 NF PF and nPnla umd PF 3 F atoms whlle P ls suf clendy large to aeeommodate 5 F atoms The argument that P has d M o desenptaon ofPFr or other hypervalmt or expanded oetetquot moleeules ansNo whlle tn FZPO the Pr 0 bonds qute strong In FZPO the assumptaon ls that there ls FZNO 152 The greater electronegativity of N also results in anomalous behavior The polarity of bonds in nitrogen compounds is o en the reverse of those in the analogous compounds of the heavier elements of the family NC13 0 3 H20 0 a NH3 g 3 HClO aq PC130 3 H20 0 a H3 PO3 aq 3 HCl g The greater polarity of the N H bond in ammonia results in ammonia being basic whereas phosphine PH3 a1sine AsH3 and stibine SbH3 are all essentially neutral Nitrogen Nitrogen does not exhibit allotropy Its only stable form is the colorless odorless diatomic gas N2 N2 comprises about 78 of our atmosphere Nitrogen is also found in naturally occurring nitrate deposits N aNO3 Chile saltpeter On an industrial scale N2 is obtained by the fractional distillation of liquid air On smaller scales it can be obtained using a zeolite to separate it from other atmospheric gases or by the thermal decomposition of ammonium nitrite or sodium azide NH4N02 aq v N2 g 2 H20 9 2 NaN3 s a 2 Na s 3 N2 g N2 is fairly unreactive at room temperature but its reactivity increases at elevated temperatures At room temperature N2 reacts with Li 6 Li s N2 g a 2 Li3N s as well as with some transition metal complexes where N2 is a weak ligand At elevated temperatures a number of other reactions are possible including reaction with alkaline earths other than Be 3 M S N2 g A M3N2 S It also reacts with 02 in the atmosphere when initiated by a lightning ash or in internal combustion engines N2 g 202 v 2 N02 g It reacts wlth H2 9 to procllee al equlllbrlum mlxmre ofNE g under appropriate eohdlaorls N2g3Hz ZN39H2 Overview nfNitrngEn Chemistry The ehemlslry of mtxogen ls eomplelr and mtxogen HKD 7 Am ranmum 3 The assumes oxldanon states from 5 to r g relauye stablllcy of the yanous oxldanon slates 7 HIGH depends on pH gt f in 1 Molecular mtxogen N2 ls thermodynamlcally g very stable as ls the ammonlum lorlNL39 ln g V and 501mm L osillr m full nl Llr 2 The oxoaclds HNO3 and HNO1 are very Flgnn ls Frusllll am im good mans agents however m base llilhquotquot soluaon Nog and NO are mueh Weaker olrldlzlng agEnts Iquot h l hm u reduemg agems m basle soluaorl N39F T w to dlspropomonanon 3 NHon all N2 g Jam all 3HrO l ANHZOH an N20 g 2 NHquot an 211 aq EHZO l Ammuniz ha a an odor only eommon gas whleh ls basle NH3 an Hzo l NTL aq OH39 aq 2 N39H l s CaOH2 s a 2 NH3 g Cacl1 s 2 H20 1 Reammns ofAmmoma Arnrnonra bums m an to gve Waist and eitheer or NO dependmg on condmons N2 rs NO rs the kmeucally preferred predict 4N39H3g3012N2g6H20l AG r1305kj 4N39H3g501 4NOg6HZOl AG r1132kJ NH3 undergoes two 6432mm reaenons wrun enlonne Wrun Excess NE N2 rs prodreed and me Hag that rs producedreads wrun the excess NE to produce souqu 2NH3g3c1le N6HCI NH2 HCI NTLCMS Wrun Excess ChNC13xs uneprodun NHg3c11e NC13I3HCI N39H reacts with Brmsted acids to form he arnrnonrurn ron MM NE W HN02 aq NH4Noz aq N11 amde ron NH NH am CH am CH4 am N39Hz39 am Propnnes ofAmmoma 39 H Arnrnonra has an abnormally mgr bodmg point 635 C comparedto phosphme m b p r 134 C due to hydrogen bondng It rs yery soluble m Waist 50 g per 100 rnL n 40 oo 30 1 Mulxula any quurd ammoma rs a polar solvent and undergoes autmomzanon 2 NH 1 NTL am NH am as BF as well as wrth trmsruor meta1rorrs N39H 9 BF 9 HNr BF 5 N1HzOo M 6 IN39Hz aq NxNTLo 6 H20 1 Haber Process rt u between Lharmodynamms and kmeues N23H2 2N39H AH 92kT AS 199J Kquot Because ofthe 5x915 of AH and AS AG beeomes wt me less rregauve andeecomes smaner asLhe temperature We we mereases Becausethe reaeuor mvolves a decreasem gt volume Lechateuer s nnnple suggests anhe W C equlh um s uld be more favorable at mgr press 5ch 5n tut Prcasum Mn r 155 persemeee yueus at usmg apressure of 200 atm and a temperature o 3mm as 5 mm m was 500 C 5 vavmus lemueramreE Uses of Ammorua sulfate or ammoruum phosphate 2 NH 3 HZSO ma NE 50 ma 3 NH 3 HePOt aq NE PO aq The Ammonium Ion The ammonium ion is colorless the most common nonmetallic cation used in chemistry Its geometry is tetrahedral and is considered a pseudoallmli metal cation with a radius close to that of K Although it is a pseudoalkali metal cation it undergoes reaction which do not occur for allmli metal ions NH4 can be hydrolyzed NHI 211 H20 0 NH 211 H30 211 it can dissociate 2 NH4CI s 1 NH3 g HCl g or it can be oxidized as when some of its salts undergo thermal decomposition NH4N02 211 N2 g 2 H20 0 NH4NO3 s a N20 g 2 H20 0 NH42CT207 5 N2 g CT203 S 4 Hz0 g Other Hydrides of Nitrogen Hydrazine 039 H Hydrazine is a fuming colorless liquid It is a weak difunctional N fH base quot H l H NZH4 aq H3O aq NZH aq H20 0 N2H4 aq 2 H3O aq a N2H52 aq 2 H20 0 Hydrazine is also a potent reducing agentwhich reduces 12 to HI and Cu to Cu NZH4 aq 2 I2 aq a 4 HI aq N2 g N2H4 aq 2 Cuzl aq H 2 Cu s N2 g 4 PF aq Hydrogen Azide Hydrazoic Acid Hydrogen azide is a colorless acidic liquid with a pKa of 19 X 10395 making it about as strong as acetic acid Although formally a hydride of nitrogen it bears no relationship to ammonia or hydrazine HN3 211 H20 0 N3 211 t H30 211 The liquid is highly toxic with an extremely disagreeable and irritating odor It is explosive and decomposes to H2 and N2 2 HN3 0 z H2 g 3 N2 g The free acid can be obtained in solution by the reaction NZH aq HNO2 aq a HN3 aq H aq 2 H20 0 The terminal NeN bond length is 113 pm between the length of a 113 m typical NN bond 120 pm and that of the NEN bond in N2 110 pm 7 p and the interior NeN bond length is 124 pm between that of the NeN N N bond length in hydrazine 147 pm and that of a typical NN bond 120 H 0 pm This can be rationalized with the following resonance structures 10 lt gt HEN H H The azide ion N3 is isoelectronic with C02 and the NeN bonds are equal in length 116 pm It is o en considered a pseudohalide 39 39 NN The decomposition of sodium azide NaN3 is the reaction that causes automotive airbags to in ate rapidly 40 ms 2 NaN3 s a 2 Na 9 3 N2 g The sodium metal is then immobilized in a series of reactions which result in the formation of glassy silicates 10 Na 2 KNO3 s a K20 s 5 NaQO s N2 g 2120s Si02s K4Si04s 2 Na20s Si02s Na4SiO4s Sodium azide can be prepared from sodium amide NaNHz by diiTerent routes 3 NaNH2 NaNO3 A NaN3 3 NaOH NH3 2 NaNH2 N20 a NaN3 NaOH NH3 Azides of PbII and HgII are used as a shock sensitive detonators in blasting caps P DN32 S Pb S t 3 N2 g Hydroxylamine Hydroxylamine NHZOH is a weak base much weaker than ammonia NHZOH aq H20 0 a NH3OH aq OH aq Kb 66 x 10399 It is prepared by the reduction of nitrates or nitrates either electrolytically or with 02 under controlled conditions Hydroxylamine is an unstable white solid In aqueous solution or as one of its salts eg NH3OHC1 or NH3OHSO4 it is used as a reducing agent NOx The Oxides of Nitrogen Nitrogen forms an array of oxides in a variety of oxidation states Each of these is thermodynamically unstable with respect to the elements but exists by virtue of kinetic stability Collectively the oxides of nitrogen are referred to as NOX Dinitrogen Oxide nitrous oxide N20 is used as an anaesthetic sometimes called laughing gas as well as a propellent for pressurized cans of whipped cream because of its solubility in fats and the fact that it is taste free and nontoxic It is a fairly unreactive neutral gas which supports combustion Mg S N20 g MgO S N2 g It is also an effective electron scavenger in radiation chemical studies 6 211 H20 9 N20 211 a N2 g OH 211 0H 211 r t m n at t t unerrnal deeornposrnon ofan aerate solutaon ofNENO NH4Noz aq N20 g 2 H20 1 N201sxsoelectxomcwlth cq and Nbut has an asymmem e N etween adouble and mplebon e ean ranon rze s 113 Pm observanon wrtn the fouowrng resonanee structures Nswo H NNO Nrtrogen Monornde nrtne ornate Nrtrogen rnonornde rs a eo1or1ess neutra1 paramagnetae gas Its pamal MO dragrarn rs srrnrlarto that of co however win one addmonal eleetron whmh rnustresrde m an annrbondmg orbrta1rts bond order rs 2V2 The ngn Energy e1eetronrnt1ne 7Eorbna1xs readny lost to form the very stable nmosyl mnNO whmh 15 xsoelectxom 11th CO The bond order 15 3 and shorter 106 pm than the bondrn NO 115 pm ere co NO forms a vanety ofcomplexes wrtn rneta1spamen1ar1y tnose m low orndanon states at low temperatures NO rs reaetave toward q ande orrrdrzenttoNo1 2N0g02 2NOZ where the eornpressed gas rnnrture eontarns both N2 and q Nng Oz 2N0g NO ean be formedby the rechlcuon of 50 HNo3 by O 3 015 8 HNO aq 3 CuNO2 aq 4HZO a 2 NO g l 5 10 Dinitrogen Trioxide Dinitrogen trioxide N203 is the least stable of the common oxides of nitrogen with A 13 139 1d 39 mol39 1 It is prepared by condensing stoichiometric quantities of NO and N02 N0 N02 g x N203 0 It is an intensely blue liquid which solidi es to a pale blue solid at 102OC Decomposition to NO and N02 is signi cant even at 30quotC N203 a x N0 g t N02 g The liquid appeals to undergo autoionization N203 Q 1 llOJr solv N027 solv N203 is the fust of the acidic oxides of nitrogen and is formally the anhydride of nitrous acid HNOZ N203 Q H20 0 2 HN02 aq N203 0 2 OH39 aq 2 N02 aq H20 0 The structure is asymmetric with an abnormally long NiN bond length of 189 pm Recall the NiN single bond in hydrazine is about 146 pm The odd 0 to N bond is shorter than the other two consistent with the resonance structures shown 189 121 pm 0 o O o Pm o N N lt gt N N J O I O 112 pmN N D 128 6 0 105 0 Nitrogen Dioxide and Dinitrogen Tetraoxide These two oxides exist in a strongly temperature dependent equilibrium N N 2 39 N AH 57 kJmol colorless red brown 15 1 1 The solid is colorless but the equilibrium constant increases with increasing temperature The liquid is pale yellow at the freezing point 11 C due to 001 N02 At the boiling point 212 C the liquid is deep redbrown and contains about 01 N02 At 100 C the vapor is about 90 N02 and dissociation is complete above about 140 C N02 can be prepared by the reduction of concentrated nitric acid with Cu Cu s 4 HNO3 aq A CuNO32 aq 2 H20 0 2 N02 g the thermal decomposition of metal nitrites CuN032 S v 0110 S 2 N02 g t 12 02 g or heavy metal nitrates 2 PbNO32 s a 2 PbO s 4 N02 g 02 g or by the oxidation of NO by 02 2 N0 g 02 g n 2 N02 g N02 is another acidic oxide which dissolves in water to form a mixture of nitric acid and nitrous acid and is a major contributor to acid rain 2 N02 g H20 0 HNO3 aq HNO2 aq O The ONO angle in N02 is 134 somewhat larger than the 39 N j 13 4o ideal trigonal planar angle of 120 This is consistent with a 0 single unpaired electron requiring less space than shared pairs of electrons The ONO angle in N204 is virtually identical 175 pm but the NiN bond length is again abnormally large at 175 pm with a bond energy of only about 57 ld39mol l O o N N 1338 j o o 15 12 Dinittogen Pentaoxide Dinitrogen pentaoXide is a colorless deliquescent solid which is the anhydride of nitric acid N205 S H20 0 a 2 HN03 211 In the liquid and gas phase the molecule has a structure similar to N204 with an O 14939 8 pm atom between the two N atoms but the 0 solid is actually an ionic substance 0 O N 1188 pm f ltd ONO39ThNO onnuae as N 2 3 e 2 13320 QNJ O O cation is called the nitronium ion and is 11 1 80 isoelectronic with C02 N20 and N31 N205 is formed by the dehydration of HNO3 by P205 2 HNO3 P205 4 HPO3 N205 or by the interaction of FN02 with LiNO3 FNO2 LiNO3 a N205 LiF The Nitrate Radical The nitrate radical is formed by the reaction of N02 with ozone N02 9 03 g N03 9 02 g and is important in nighttime atmospheric chemistry In daylight it is photolyzed to NO or N02 N03 9 No 9 02 9 N03 9 L Now 09 1513 In the absence of light it reacts with allmnes or alkenes in the environment to form strongly oxidizing products Q 9R H9 quotR9 Nos 9 Nitrogen Halides Nitrogen trichloride NC13 is an oily yellow liquid as is characteristic of covalent chlorides It undergoes hydrolysis to ammonia and hypochlorous acid N013 aq H20 0 a NH3 g 3 HClO aq These products are consistent with the expected polarity of the 6 TI 6 N 7 C1 b d 39 on C I N H The compound is explosive when pure but the vapor is used AF H industrially as a bleaching agent for our 6 6 Nitrogen tri uoride NF3 is a thermodynamically stable colorless odorless gas of low reactivity and is stable to hydrolysis Unlike NH3 it is a poor Lewis base and has FiNiF bond angles of about 102 This is consistent with Bent s Rule which suggests the hybrid orbitals used in bonding to F are high in p character and the orbital in which the lone pair resides is high in s character F NF3 reacts with 02 gas at low temperature to form a compound with a F I coordinate covalent bond between N and O N O F 2 NF3 g 02 g A 2 FsNO g Nitrous Acid and Nitrites Nitrous acid is a weak acid that can be prepared by the action of a strong acid on a nitrite salt BaN022 aq H2804 aq 2 HN02 aq BaSO4 s It is unknown in the liquid state but has been observed in the gas phase In solution it undergoes slow disproportionation at room temperature and the rate speeds up at elevated temperatures 3 HNO2 aq HNO3 aq 2 NO g H20 0 1514 The nitrite ion is an oxidizing agent which is capable of oxidizing many common ions including Fe and I39 HNO2 aq H aq e39 a NO aq H20 0 EO 10 V As a result nitrites of metals in low oxidation states cannot be prepared Sodium nitrite is used as a preservative for fresh and cured meats because it inhibits the growth of bacteria When used with fresh meat it oxidizes hemoglobin to methemoglobin which resists oxidation Nitric Acid and Nitrates Nitric acid is a colorless oily liquid when pure and is extremely hazardous It is a strong acid as well as a strong oxidizing agent Although colorless when pure the acid may appear yellow due to trace NO2 which results from photolytic decomposition h 41403011 39 4m290292 120l The pure liquid undergoes slight autoionization 3 HNO3 a e NO HNO3 H30 HNO3 2 NO HNO3 Concentrated nitric acid is a 70 aqueous solution which is about 16 M in HNO3 Fuming nitric acid is an extremely potent oxidizing agent and is a red solution of NO2 in pure HNO3 The first industrial synthesis of nitric acid used a mixture of N2 O2 and water in an electric arc fumace to produce HNO3 directly The arc lmace was needed to overcome the large activation barrier 2N2g502g 2H20g4HN03g Fortunately this barrier exists Ifnot for it our atmosphere would have high HNO3 concentrations and our lakes and oceans would be nitric acid Today the Ostwald Process is used to prepare nitric acid 4 NH3 9 5 029 gt 4 N0 9 6 H20 9 2 NO 9 02 9 2 N02 9 3N02 9 H20 I gt 2HN03 I NO9 The Lamina NeObohds m HNO3 are shorter 121 pm thm the Ne oeH bond 141 pm but all three bonds m the nmate 1oh are equal m 1ehgth 122 pm Nm39ates of most meta1s m eommoh ohdataoh states are known and are so1ub1e mahmg these sa1ts 141m eohvemeht sources of a vanety of eataohs Nnxaee 1oh1s soohg1y ohdmhg oh1y m and sohmoh so mtxates ofmetals mloweroxxdahon states can be 1so1atedlte g FeNO2 Th most 1mpmantmtxate mohsma11y1s ammomum mtxatewhch ean be obtahedby reacting ammoma wnh mm and NE W HN02 aq NH4Noz aq 122 pm N39HaNOZ 15 usedm eo1d packs beeause the dassolunon ofNENO 15 mdotha mm N39HaNOZ s N39H aq No aq AH 26kJ AS 11 01Kquot m n exp1os1ve1y at hgher temperatures N39HaNOZ s a 2 H20 g N20 9 2NH4N025quot2N2301E4H20 thsphnnls Chemistry Unhke mtxogEn the hgher ohdataoh states of mint I n e m mm 15 16 Allotxopes of Phomhoms Phosphoms has several allotxopes whxte red and black phosphoms The snmplesL and least nablc is whxte phomhoms somchmcs called ycuowphosphoms Whnep omhomscsa xg ytmac tewaxy derwater Ins solublcm common nonrpolar schants P s 5 O 9 Psom s umts Red phomhomsxs msolublem common solvents prepare Blackphosphoms has a complex polymm somcnnc shown below ande prepared by hcahng whne phosphoms under ememe pressure 1517 Extraction of Phosphorus Phosphorus is prepared from naturally occurring calcium phosphate Ca3PO42 in an energy intensive process 180 000 A 500V and 1500 C 2 6030042 s 10609 A 66005 10 002 s P4 9 Compounds of Phosphorus Phosphine Phosphine PH3 is a colorless extremely toxic gas Unlike ammonia phosphine is sparingly soluble in water and an extremely weak base The P H bonds are much less polar and phosphine is incapable of hydrogen bonding It can be prepared by combining an active metal phosphide with water or dilute acid C21st S 6 H20 0 PHs g 3 Ca0H2 211 The HiPiH bond is only 930 compared to about 1070 for the HiNi H bond P in ammonia This suggests that phosphorus uses pure p orbitals rather than sp3 H H hybrid orbitals for bonding to H The lone pair is essentially in the s orbital Phosphine itself has limited utility but substituted alkyl and aryl phosphines are IllP Pmquotl common in coordination chemistry H30quot I CH2CH2 39CHS H36 CH 3 dmpe Oxides of Phosphorus Phosphorus forms two molecular oxides representing the 3 and 5 oxidation states Both are white solids at room temperature Tetraphosphorus hexaoxide P405 is formed by heating white p phosphorus in an oxygen de cient environment The structure of 0 0 P406 consists of a tetrahedron of phosphorus atoms with bridging oxygen atoms between the P atoms rather than P P bonds I POP 1 0 ms 3 029 A P4066 0 1518 Tetraphosphorus decaoxide P4010 is formed by heating white 0 phosphorus in an excess of oxygen The structure of P4010 is based on the P406 structure with terminal 0 atoms bonded to each P atom P A P4 5 5 02 9 P4010 S O O l 0 l o Tetraphosphorus decaoxide is a potent dehydrating agent and P I 7O forms phosphoric acid as it absorbs water 0 O P O P4010 S 6 H20 Q a 4 H3PO4 aq i It is capable of dehydrating nitric acid to N205 Halides of Phosphorus Phosphorus forms two series of halides PX3 and PXS representing the 3 and 5 oxidation states respectively Trihalides other than PFS are formed by the direct reaction between the halogen and an excess of phosphorus PF3 is formed by the uorination of PC13 P4S 6029 gt 4PC3 Pentahalides other than PF 5 are formed by the reaction of phosphorus and an excess of the halogen PF5 is formed by the reaction of PC15 with CaF2 at 3004000C P4 5 10 a2 g 4PCI5s Unlike NCIS which is hydrolyzed to NH3 and HClO PCl3 is hydrolyzed in a multistep process to phosphonic acid commonly referred to as phosphorous acid PC13 0 3 H20 0 a H3PO3 a 3 HCl g PCl5 undergoes hydrolysis to phosphoric acid in a series of steps The rst step yields phosphoryl chloride alm phosphorus oxychloride POCl3 POCIS subsequently undegoes further hydrolysis to the acid PC15 s H20 0 a POC13 0 2 HCl g 130013 03 H20 H3PO40 3HC1 g 1519 PCl3 has atrigonal pyramidal geometry due to the lone pair on P P39 In I CI quotCI PCl5 has a trigonal bipyramidal geometry inthe liquid and vapor phase Cl However in the solid phase it exists as an ionic compound POLY PC1639 where the cation is tetrahedral and the anion is octahedral in geometry CI CI Cl 39 C C39 quotquotll PI J CI P a 39I39 Cl P CI CI CI 0 I 539 CI CI Phosphorus Oxychloride Phosphorus oxychloride is a dense toxic liquid which reacts with trace moisture in the air and is the sta1ting material for a great deal of phosphorus chemistry It is produced on an industrial scale by the catalytic oxidation of PC13 2 PC13 0 02 g a 2 POC13 0 although it can also be prepared by the reaction of PC5 with a stoichiometric amount of water PC15s H20 130013 a 2HC1 g 1520 Phosphorus Oxoacids Phosphorus forms a series of oxoacids with interesting properties phosphoric acid H3PO4 phosphonic acid commonly referred to as phosphorous acid H3PO3 and phosphinic acid commonly referred to as hypophosphorous acid H3P02 In an oxyacid a hydrogen atom is ionizable if it is bonded to an oxygen atom In most series of oxoacids terminal oygen atoms are typically lost as the oxidation state of the central atom decreases For example sulfuric acid and sulfurous acid whose structures are shown are both diprotic T acids quot Squot 5quot H O I quot39o H ol 39 o O O H H However as we proceed from phosphoric acid to phosphorous acid to hypophosphorous acid bridging O atoms are lost leaving an H atom bonded directly to P As a result those H atoms are not ionizable and while phosphoric acid is a triprotic acid phosphorous acid is diprotic and hypophosphorous acid is monoprotic l l l P P Pl H Ol O H H Ol quotH H O quotH O O H H H Phosphoric Acid Pure orthophosphoric acid is a colorless syrupy liquid and a concentrated aqueous solution of the acid is 85 by mass H3PO4 with a molar concentration od about 147 M Unlike nitric acid it is essentially a nonoxidizing weak triprotic acid H3P04 aq H20 0 e H2P04 aq H30 aq H2130 ltan H200 e HP042 aq H30 aq HP042 211 211 H20 0 r P04 aq H30 211 1521 The pure acid is obtained by the thermal process which involves buming white phosphorus in excess oxygen to produce P4010 and then treating the oxide with water P4 5 5 02 g P4010 S P4010 S 6 H20 9 4 H3P04 aq It can also be prepared by treating calcium phosphate with sulfuric acid in a process known as the wet process 021303042 s 3 HZSO4aq 3 CaSO4s 2 H3PO4aq Heating phosphoric acid leads to the loss of water and the l IT formation of a series of condensed phosphoric acids The rst of these is pyrophosphoric acid H4P207 2H3Po4a i H4P2070 H200 Further condensation leads to triphosphoric acid H5P3010 A 3H4P207 gt 2 HsPsoioG H200 Metaphosphoric acid is polymeric quotH3P04 Lgt H Osn nHzOU HO ioioH HO HO pyrophosphoric acid ii i oiOioioH o H0 PP Triphosphoric acid H O l 0 0 metaphosphor39ic acid l 522 Phosphates The phosphate ion PO4339 is very basic and subject to hydrolysis in aqueous solution Hydrolysis leads to the formation of hydrogen phosphate dihydrogen phosphate or even phosphoric acid depending on pH P0437 211 H20 0 v HP042 211 OH 211 HPO4239 aq H20 Q H2P0439 aq OH aq HzPor aq H20 0 e H3P04 aq OH aq With the high charge of the phosphate ion most phosphates have relatively high lattice enthalpies and are typically insoluble Only those of the allmli metals and ammonium ion are soluble Sodium phosphate Na3PO4 is very basic and is used as an effective degreaser and industrial cleaner known as TSP for trisodiurn phosphate Solid hydrogen and dihydrogen phosphates are only known for monopositive cations and the larger dipositive cations Recall that large anion are only stabilized by cations of low charge density The Remaining Elements Hydrides The stability of the hydrides decreases going down the family This is primarily due to the decreasing XeH bond strength as X becomes larger and orbital overlap becomes less effective NH3 gt PH3 gt AsHs gt SbHs gt BiH3 J Tba39mally unstable The basicity decreases in the same order l 523 Halides Arsenic trihalides may be hydrolyzed to a1senous acid like the phosphorus ttihalides AsClg Q 3 H20 Q a H3As03 Q 3 HCl g Antimony and bismuth ttihalides yield oxychlorides in reversible reactions BiClS 0 H20 0 BiOCl s 2 HCl aq Pentahalides especially the uorides of P As and Sb are very good Lewis acids but the ttihalides are not Lewis acids Oxides The stability of higher oxidation state decreases with increasing atomic number For example bismuth V oxide has never been isolated as a pure substance In a given oxidation state the metallic character of the elements and therefore the basicity of the oxides increases with increasing atomic number increasing basicity gt P406 lt AS406 lt Sb406 lt Bi203 l acidic ampho rer ic basic 111 Chapter 11 The Alkali Metals Common Features Element mp OC 7Hmm All of the alkali metals have high electrical and thermal kJ 39m 01391 conductivities which are characteristic of metals Li 180 162 Unlike other metals however all of these metals are very Na 98 108 so and this trend increases going down the group This K 64 90 so ness is the result of very weak metallic bonding There is a strong correlation between the so ness low melting Rb 39 82 pomt and small enthalpy of atomlzatlon CS 29 7 8 The metals have very low densities Lithium is the least dense of all metals as well as the least Element Densny g39cm 3 dense solid element Its density is 053 g 39 cm393 Cesium is Li 03953 the most dense of all the allmli metals but its density is only Na 097 187 g 39 cm393 K 086 The metals are very reactive Rb 153 All of them react with 02 and are kept under oil or in the cs 137 case of the more reactive metals under a vacuum All react with water and the reactions become more vigorous going down the group Ionic Compounds All of the metals form a stable 1 cation and the vast majority of Ion A thd the compounds are stable ionic solids kl mol39 1 Li 5 19 These compounds are colorless unless the anlon imparts a color to the compound e g MnO439 CrO4239 Cr2072 Na 406 The cations are capable of stabilizing large low charge anions KT 322 such as HCO339 In fact the alkali metals form the only stable Rb 3 0 1 b1carbonates Cs 275 Except for Lil and a few Nal salts the salts are anhydrous l 12 Solubility of Allmli Metal Salts Salts of these ions are typically water soluble Solubility depends on AG for the process MX S Ml 211 t X 211 Two contributions to AG AG AH TAS We can write a Hess Law cycle to relate AH for the process in terms of the lattice enthalpy U and the enthalpies of hydration of Ml and X39 MX s a M g X g AH U M g M aq AH Athd M X g r X aq AH AHrryd X MX s M aq X aq AH U Athd M Ade X39 For the sodium halides U z Athd Ml Athd X39 so AH for the dissolution of a sodium halide is typically close to 0 meaning that the solubility is an entropy driven process So the solubility of NaF is less than 1 mol per liter while those of the other sodium halides are larger and increase with increasingly negative AGg oln values It should not be surprising that the calculated AGg oln values parallel the measured solubilities because there is a wellestablished relationship between AG0 and K for a process AGO RTan MX S M g X g K Mlllx39 Homng the solutnhnes othe salts ofa particular hahde as afuncnon othe eanon mdaus we geta smooth curve For andF39 Lheplots are shown In general solubnhty W11le greatest when there 15 a on mdn larger mxsmatch m the eanon and am Hydranon Data for the Alkah Metal Ions Solubmly LR No EU Rb rs Canon radius gt Figure 112 sexumlm ofaVkah mexa uorides and Ud des as a funchcn oi alkah metal 0 radms Secondary hydranon layers vary m sue mversely wnh the bare eanon nadms That 15 the larga39 naked of the canon 114 Qualitative Analysis Since most of the alkali metal ions form soluble ionic compounds precipitation is generally not used as the basis for identifying them in qualitative analysis schemes Na and Kl belong to Group V in the qual scheme The allmli metals exhibit distinct colors in ame tests Li Na K Rb Cs crimson yellow lilac redviolet blue In the ame the ion acquires an electron from the combustion process and is excited to a higher electronic energy state The excess energy is then lost in the form of an emitted photon whose enrgy matches that of the dilTeIence between the two energy levels of the atom 3p 3s 3p emission of 5892 nmphoton 39 3s 1 3p thermal gt emitation 3 S The Elanants and physical propemes um m The Fundamental Properties of the Group 1A Elements Ref 32 m mm mm mm mm Sywbul x N x m c Amm mm w n w 37 55 a7 Nmmmmm 51 2 72mm 39mm 857215 133100 223m A abundant 79 ss wmmx 8127 16 max Tum m m wow i 7 u 17 21 30 Arwmcwrvghl am you saw am v 225 Vanm 1mm 16 3 an 539 69 w c asms 975599 sassW ism6K2 usmm 17677 nsu wm um I 53 1 m A unwum A 157 1 u 1 so 2 72 1mm mdrn Slum wmwAu N u 714 1 m4 mm man mm mam m u n u m ox n 7 w Livan denmy chargelom mdmsh un39z n NA m Lon m 055 n 7271 la rm 7 292 0 onslrc A 1 Y n L nunmm 5nd n W szu m 419 4m 3m mam mm umnl 58 53 43 r n 745 Dhcmncd Wm An vadxn Davy Um nun sum Percy m7 mm mm Klmhlm 39 Knchhn um mm mm 1 the Naju 140 m mg K01 Ana bm Maxch Mmide 13w sm Bu Bis am my a Non Nuns Nun WM H xx 11X cg quotmm en K Rbquot an mm unvmure m hm um um WW 391 um my r vowmml M Um rm mum QM 116 Lithium As mentioned the least dense of all the elements that are solids at SATP Li reacts with 02 to give Li20 Other elements give peroxides and superoxides when reacting with 02 Unlike the other alkali metals and the majority of the other elements Li reacts directly with N2 yielding Li3N 6 Li s N2 g a Li3N s The compound has an extremely high lattice enthalpy due to the large charge on N339 and the very small radius of L 90 pm This large U compensates for the extremely high bond dissociation energy of N2 945 ldmol The N339 ion is very basic and Li3N is very reactive yielding NH3 on exposure to H20 Li3N s 3 H20 0 a 3 LiOH s NH3 g Liquid Li is extremely conosive and Li has the most negative E0 of any element L aqe39 a Lis E 305 V However the slow reaction with water is a re ection of the large activation energy The largest industrial use is in lithium grease 60 of all automotive grease contains lithium in the form of lithium stearate C17H35COOLi mixed with oil to form a water resistant mixture which does not harden in cold temperatures but has a high thermal stability The relatively high solubility of lithium compounds even simple ionic compounds such as LiCl in lower polarity organic solvents e g ethanol and acetone indicate a signi cant degree of covalence consistent with the highly polarizing Li ion nbutyl lithium is a useful alkylating agent in organic chemistry nbutyl lithium is an extremely reactive and basic liquid which is typically handled in a solvent of low polarity 2 Li s C4H9Cl C6H12 a LiC4Hg CH12 LiCl s It combusts spontaneously on exposure to 02 in air Another important industrial use of lithium is in batteries Several diiTerent lithium batteries have 117 been developed but they share the characteristics of relatively high potential due to the large reduction potential of L and low mass due to low density of Li The anode reaction involves the oxidation of Li to LY EO 305 V 11 8 Sodaum sum 4mm Manufactured by me Downs Process Kmquot 2 NaCl 1 e 2 Na 1 c12 g mum mm m 1 C 772 C 15 used A mmmre of 33 NaCl mp 80 and 67 cm1 mp ms is the summit mxxmre andhas a mp of m 580 C mm Chfo uses are as 1 cpmmemml reduemg agent for other metals TxCL l4Nas T s4NaCl s 2 w dw N an annknock addmve 4 Nan s 4 cszq 9 camp I 4 NaCl 5 3 Pb 5 Potassium Potassium 15 predicted by Nareohctmn of Kc1 because electrolysis ofmoum KCl 15 too danga39ous ue to the ma reamva othmdpotassmm Na 1 Kc1 a e K g NaCl 1 T xsmc 850 stbetweenthe bmlmg pmms ofNa 890 C de 766 C equlhbnum emsmm m accord mm LeChateher39s Pnnmple each other m sue NaBF has a solubxhty m waeer of 108 g moo mL but me solubxhty of KBF 15 only 4 44 g non mL 119 Allmli Metal Oxides All of the metals react directly with 02 but only Li gives the oxide 4 Li s 02 g a 2 LiZO s Sodium reacts to give the peroxide also known as dioxide 2 2 Na s 02 g a Na202 s Potassium rubidium and cesium give the superoxide also known as dioxide 1 MS 02g M02S 02239 is diamagnetic with rOO 149 pm 7 Aquot h bondorderil 2 A Tan 3 2 5517 0239 is paramagnetic with rOO 133 pm bond order 32 020 1 unpaired electron a 02 is paramagnetic with rOO 121 pm 3 quot 39 3 bond order 2 H10 2 unpaired electrons The least polarizing largest cations can stabilize the most pola1izable anions The oxides react with water to yield hydroxides peroxides yield hydroxide and hydrogen peroxide and the superoxide yields hydroxide hydrogen peroxide and 02 LiZO s H20 0 a LiOH aq Na202 s 2 H20 0 a 2 NaOH aq H202 aq 2 K02 s 2 H20 0 a 2 KOH aq H202 aq 02 g Potassium superoxide is used in enclosed spaces as a scrubber for C02 and H20 4 K02 s 2 C02 g a 2 K2C03 s 3 02 g K2C03 s C02 g H20 g a 2 KHCO3 s ll 10 Alkall Metal Hydroxldes e solldnydromdes are colorless wlute translucent sollds ExceptforLlOHthy are dellquescent Tnatrs tlney absorb molsture from Lhelr surroundngs and eventually dssolye m tlne cumulatedwater LlOH form a stable octahydrate LlOH 8 H20 r t solubllltyls anlssue NaOHls preparedbytlne electrolysrs ofbnne concentrated aqueous NaCl 3 differmt cells are m common use In each or ls omdzedto Cl1 attlne anode buttlne catlnode reactlon yanes aphr membrane cells H20 ls reduced to H2 g and OH andtheresulung electrolyte contans ddssolvedNaOH wlncln can be recovered 1n tlne mercury process tlne catlnode ls a mercury electrode and e to H2 oyeryoltage Na ls redrcedto a Na amalgam wlucln ls lsolated and allowedto react wrtln water to yleld NaOH NaOH ls perenmally m tlne top 10 rnorgamc chemlcals m terms of quantrues produced and has many lndusmal and household uses unn u untwmceu Na KClNa1CO3 and Nch03 are all lmportantlndustnally and economcally Thar uses are dlscussedln tlnetext Ammoma Reactron Alkle metals dssolye m quuld ammoma to gve deeply blue colored solutrons The solutrons electrons Na 5 Na am e39 am metal yreldsodum amlde alde 2Na39am2NEl 2e39am NaNH2amH2g Transition Metal and Coordination Chemistry Transition metal A metal which has a partially lled d subshell either in the neutral atom or in a common oxidation state These are generally hard and strong metals which conduct heat and electricity quite well They also tend to have high melting points These metals o en form colored and paramagnetic compounds due to their partially lled d subshells Coordination complex A metal ion or atom with one or more molecules or ions referred to as ligands joined formally by coordinate covalent bonds Coordination number The number of donor atoms directly bonded to the metal atom ion Coordination numbers of 4 and 6 are the most common and important Ligand A Lewis base ion or molecule covalently bonded to the metal atom or ion Coordination Sphere The metal center along with all the ligands bonded to it Types of Ligands l Monodentate Ligands literally meaning onetoothed are those ligands which coordinates through only one atom Some examples are F39 Cl39 H20 NH3 PCH33 etc 2 Polydentate Ligands are those ligands which coordinate through two or more donor atoms simultaneously These are also referred to as chelating ligands when the donor atoms are bonded to the same metal center Bidentate ligands coordinate through two donor atoms Some examples are 22 bipyridine 110phenanthroline ethylene diarnine and acetylacetonate Q FENCE aim ma a1 0 22Lbjpyrjdjm bpy ethylenediamjm en acetylacetonate acac 110plemnhrolim phen Tridentate ligands coordinate through three donor atoms Some examples are 22 6 2quot terpyridine and diethylenetliamine H CHZ CH I CH2 CH2 22396392quot terpyridine tlpy diethylenetriamjm dien Tetradentate ligands coordinate through four donor atoms Some examples are macrocycles such as the valious porphyrins and phthalocyanines porphyn39n phthalocyanine O O Hexadentate ligands coordinate through II II O c CH2 CHz O O s1x donor atoms A very common example is ethylenediaminetetraacetate N CHZ CHZ N 2 EDTA O CH CHz C O O ethylenediamjnetetraac etate Ambidentate ligands are those ligands which can coordinate through either of two diiTerent donor atoms Some common examples are the thiocyanate anion which can coordinate through either the S or N atom and the nitrite ion which can coordinate through either the O or N atom GEN N s n o o SCN39 thiocyanatoi S NOZ39 ninitoiN formerly called nitro NCS39 thiocyanatoiN ONO39 nitritoio Some Common Ligands Common name uoro F39 chloroC139 bromo Br iodo I cyano CN thiocyano SCN isothiocyano NCS hydroxo OH aqua HZO carbonyl CO thiocarbonyl CS nitrosyl NO nitro NOZ nitrito ONO39 phosphine PR3 pyridine CSHSN ammine NH3 cthylenediamine N39HZ CH2 CH2 NHZ diethylinetriamine N39HZ CZH4NHCZH4N39HZ triethylenetetramine N39HZ CZH4NHCZH4NHCZH4N39HZ 3 3 triaminotriethylamine NC2H4NH23 IUPAC name uoro chloro bromo iodo cyano thiocyanatoS Sbonded thiocyanatoN N bondcd hydroxo aqua carbonyl thiocarbonyl nitrosyl nitritoN N bonded nitritoO Obonded phosphane pyridine ammine 12ethanediamine 1 47triazaheptane 22 diaminodiethy1amine 14710tetraazadecane 3 3 tris2aminoethy1amine Abbreviation F Cl39 co cs No No ONO dien trien tren Common name acetylacetonato CH3COCHCOCH339 2239 bipyridine csH4NicsH4N 110phenanthIoline 12 2 26 2quotterpyridine dialky 1 dithiocarbamate 12bisdipheny1phosphinocthane C th 0pheny1enebisdimethy1arsine C6H4ASCH3 Z Z dimethylglyoxime ethylenediaminetetraacetate 139UPAC name 24 pentanediono 22 bipyridy1 1 10diaminophenanthrene dialkylcarbamodithioate 12ethanediy1bisdipheny1pho sphane 12pheny1enebisdimethy1arsane butanediene dioxime 12ethanediy1dinitrilotetraac etate 194 Abbreviation acac bpy bipy phen FY tpy dppe diars DMG ED TA CH3 CH3 OH N N OH o H e o C CH2 N CHZ CHZ N o C CHZ EDTA 0 ll 0 MefS SMe 391 Me Me Ph Ph diaIs 1 CH CO s R 2 fic N CHZ CO s R Me dtc acac The Chelate Effect It is generally the case that formation constants for complexes involving chelating ligands are substantially greater than those for complexes involving monodentate ligands For example we can compare the formation constant of CuNH342 with that of Cuen22 The latter is 75 orders of magnitude higher CuH20412 aq 4NH3aq e CuNH342aq 4H20a 10991259 CuH20412 aq zen aq e Cuen22aq 4H20a IogKf2003 A larger Kf re ects a more negative value of AG which could result from a more negative AHO or a more positive AS RTan AGO AHO TASO There is little dilTerence in the values of AH0 for the two reactions so the difference must lie in the values of AS The reaction of NH3 with CuH2042 involves no change in the number of molecules in solution and is therefore to a rst approximation entropy neutral The reaction of en with CuH2042 however leads to an increase in the number of molecules in solution and therefore has a positive value of AS The chelate effect is therefore a re ection of the more favorable entropy change accompanying the formation of a chelate complex relative to that of a complex with monodentate ligands The effect is even more pronounced when ligands such as EDTA form complexes and these complexes have very large formation constants EDTA in fact is used as an analytical reagent for tittating metal ions Isomerism Coordination complexes or compounds may have the same formula but different structures These di erent forms are referred to as isomers Co ordination Comp ounds Structural Isomers Stere ois omers different bonds identical bonds Linkage C oordination Sphere Coordination Geometric Optical Isomers Isomers Isomers Isomers Isomers Ionization Hydration Isomers Isomers Stereoisomerism Geometric Isomerism Geometric isomers typically exhibit distinct chemical and physical properties Geometric isomerism does not occur in tetrahedral complexes however it does occur in square planar and octahedral complexes oistrans isomerism occurs in square planar complexes of the general formula MXZYZ and octahedral complexes of the formula MX2Y4 As in organic chemistry the cis designation refers to the like ligands being adjacent to each other while the trans designation refers to the like ligands being opposite each other tetraaquadhhlorochromimn Ill diamminedicl oroplatinmn H CI CI NH3 HC OHZ CI CI P1 quot C CI P1 quot NH3 HZO CHHZ HZO CF39 OH2 H3N H3N HZOI HZO CI H2 trans cis trans 0139 s Facial and meridional fac and mer isomerism occurs in octahedral X X complexes of the formula MX3Y3 The I 39X I I fac designation refers to the like ligands y occupy adjacent comers of a triangular y I I face of the octahedron all at 900 to y X each other while the mer designation refers to the like ligands occupying fac mel coplanar sites with two of them at 1800 with each other Optical Isomer39ism Molecules which are nonsuperimposable on their mirror images are optical isomers enantiomers These molecules rotate plane polarized light in equal but opposite directions They have identical chemical properties and reactivities except in a chiral environment Optical isomerism occurs when a molecule lacks an improper axis of rotation including a plane of symmetry and a center of inversion Therefore square planar molecules will not exhibit optical isomerism but octahedral and tetrahedral molecules can In the case of octahedral enantiomers the molecules are designated as A or A depending on their absolute con gurations X X N I N quot39 39 quot39 Z M39 v Y M Z N M N NM Z I Z N I I kl NJ y l y N i N I I mirror plane mirror plane A E A N i N AIA Al l B ICIquot39D i NM39quotNI39I i HrNquot iN mirror plane mirror plane Structural Isomerism Linlmge Isomerism Linlmge isomerism can occur when a complex contains an ambidentate ligand such as SCN39 or NOZ39 The complex ion CoNH35N022 illustrates this type of isomerism The complex ion with the N bonded nitrite ion is yellow in color while the ion with the O bonded nitrite ion is red in color 0 2 N ONO 2 3 NH3 NH3 H3N7Co NH3 H3N7Co NH3 H3N H3N NH3 NH3 yellow red It should be pointed out that although such isomerism is always possible when an ambidentate ligand is present it is not always the case that both isomers are isolable In some instances a particular metal center will prefer to bond to one donor atom or the other For example SCN39 typically bonds to so metal ions using the S atom and to harder metal ions using the N atom Coordination Sphere Isomerism Coordination sphere isomerism includes ionization isomerism and hydration isomerism Ionization Isomerism Ionization isomers give di erent ions when dissolved in solution Two di erent compounds with the formula CoNH34C12N02 exist One of them yields a precipitate of AgCl when silver nitrate is added to a freshly prepared solution while the other does not A Cl ion within the coordination sphere will not be precipitated while one outside the coordination sphere will be Therefore the compound that yields the precipitate must have its Cl ions within the coordination sphere while the other has one outside the coordination sphere coNH34CI21 N02 s coNH34CI21 aq N0239aq corNH34cIN021cI s E corNH34cIN021 aq C39oq Hydration Isomerism Hydration isomerism is similar to ionization isomerism but it is water molecules that may be inside or outside the coordination sphere For example there are three diiTerent compounds with the empirical formula CrCl3 39 6 H20 One of these is Violet in color loses no water over sul lric acid and all of its chloride is precipitated from a freshly prepared solution From this data we can determine that the water OH2 3 molecules are all within the coordination sphere and all of I II 0H2 the chloride ions are outside the coordination sphere H20 Cr LOH2 Therefore this coordination compound is H20 I 0H2 CrH2053 3 or or CrH205 013 The second is green in color loses 16 of its water over sul lric acid and b of its chloride is precipitated from a freshly prepared solution From this data we can determine that one of the water Cl 2 molecules is outside the coordination sphere and only two I IIIIOH2 of the three chloride ions are outside the coordination H20 Crquotquot OH2 sphere Therefore this coordination compound is H20 I 0H2 CrC1H2052 2 cr H20 or CrC1H205C12 H20 The third is also green in color loses a of its water over sul lric acid and a of its chloride is precipitated from a freshly prepared solution From this data we can determine that two of the water II III39 OH molecules are outside the coordination sphere and only 2 O Cr39 OH one of the three chloride ions are outside the coordination 2 0 I 2 2 sphere Therefore this coordination compound is CI CrC12H204 cr 2 H20 or CrC12H204C1 2 H20 Incidentally the Cl ions in the coordination sphere are trans to each other l 9 10 Coordination Isomerism Coordination isomerism not to be confused with coordination sphere isomerism occurs when both the cation and the anion of a coordination compound are complex ions In this case the distribution of ligands in the cation and anion may vary For example each of the following is a pair of coordination isomers C0mNH36lC1mCN6l and CIHINH3s C0mCN6l Crul NH3s C111 ISCNkl and CImNH34SCN2 CImNH32SCN4 PtHNH34PtIVC6 and PtWNH34012lPtll Ch Nomenclature of Coordination Compounds 1 The names of neutral coordination complexes are written without any spaces Ionic coordination compounds are written as two words with the cation first and the anion second In naming a coordination complex or a complex ion the names of the ligands listed alphabetically are given first followed by the name of the metal and nally the oxidation state of the metal or the charge on the complex is given last A The number of ligands of one kind is given by the following pre xes Ifthe ligand name includes one or more of the these pre xes or is otherwise complicated it is set OH in parentheses and the second set of pre xes is used 2 di bis 3 tri His 4 tetra tetrakis 5 penta pentakis 6 hexa hexakis 7 hepta heptakis 8 octa octakis 9 nona nonakis l 0 deca decakis p Ligands are named in alphabetical order according to the name of the ligand not the pre x although exceptions to this rule are common An earlier rule gave anionic ligands first then neutral ligands each listed alphabetically 1911 C Anionic ligands are given an o suf x Neutral ligands retain their usual name with some exceptions Neutral ligands are usually given the same name as the uncoordinated molecule but with spaces omitted Speci c examples are CH3ZS O dimethylsulfoxide DMSO NH22CO urea C 5H5N pyridine terpy terpyridine bpy 22 bipyridine 02 sulfurdioxide N2 dinitrogen O2 dioxygen PC13 trichlorophosphine PPh3 triphenylphosphine OPCH33 trimethylphosphineoxide POCH33 trimethylphosphite There are however some neutral molecules which when serving as ligands are given special names These are NH3 ammine H20 aqua NO nitrosyl CO carbonyl CS thiocarbonyl Anionic ligands are given names that end inthe letter quot0quot When the name of the free uncoordinated anion ends in latequot the ligand name is changed to end in quotatoquot Some examples are CH3C0239 acetate acetato 804239 sulfate sulfato CO3239 carbonate carbonato acac acetylacetonate acetylacetonato When the name of the free uncoordinated anion ends in quotidequot the ligand name is changed to end in quotidoquot Some examples aie N339 nitride nitrido N339 azide azido NHZ39 amide amido H39 hydride hydrido When the name of the free uncoordinated anion ends in quotitequot the ligand name is changed to end in quotitoquot Some examples are NO nitrite nitrito 803239 sul te sulfrto Certain anionic ligands ale given special names all ending in quot0quot CN39 Cl 02239 OH39 cyanide cyano F39 chloride chloro Br iodide iodo 0239 peroxide peroxo 0239 hydroxide hydroxo CH3O uoride bromide oxide superoxide methoxide 1912 uoro bromo oxo superoxo methoxo Organic groups although implicitly considered to be anions are given their regular names without an quot0quot CH3 C2H5 C3H7 CsHs 3 Two systems exist for designating charge or oxidation number ending Some examples are Me methyl Et ethyl Pr propyl Ph phenyl A The Stock system puts the calculated oxidation number of the metal ion as a Roman numeral in parentheses a er the name of the coordination sphere This is the more common convention although there are cases where it is di icult to assign oxidation numbers B The EwensBassett system puts the charge on the coordination sphere in parentheses a er the name of the coordination sphere This convention is used by Chemical Abstracts and olTeIs an unambiguous identi cation of the species In either case if the charge is negative the suf x ate is added to the name of the coordination sphere In some cases the suf x is merely added to the name of the metal cobalt Co zinc Zn cobaltate zincate bismuth Bi nickel Ni bismuthate nickelate In some cases the ending of the name of the metal such as um or ium is dropped before the suf x is added chromium Cr osmium platinum chromate ruthenium Ru Os osmate Ihenium Re Pt platinate vanadium V ruthenate rhenate vanadate In some cases more than just the um or ium ending or an ending other than um or ium is dropped before the suf x is added manganese Mn manganate tungsten W tungstate molybdenum Mo molybdate 1913 In some instances the name of the anionic complex is based on the Latin name of the element iron Fe ferrate lead Pb plumbate silver Ag argentate tin Sn stannate antimony Sb stibate gold Au aurate copper Cu cuprate 4 The pre xes cis or trans and fac and mer designate adjacent and opposite geometric locations The pre xes fac and mer also distinguish geometric isomers 5 Bridging ligands between two metal ions have the pre x pi Examples potassium hexacyanoferrateIII K3FeCN5 potassium hexacyanoferrate3 hexaamminecobaltIII chloride CoN H 35C13 hexaamminecobalt3 chloride dichlorobisethylenediaminecobaltIH Coen2C12 dichlorobisethylenediaminecobalt1 tn39Sbipy diIIeiI0nH FebPY32 trisbipyridineiron2 hexacarbonylmolybdenum0 MoCO5 sodium amminetrichloroplatinateII NaPtC l 3NH3 sodium amminetrichloroplatinate2 cz39s tetraamminedichlorocobaltIII cis CoC 12N H3 4 cz39s tetraamminedichlorocobalt1 mer uicl uru u ixltl 39139 39 39 39 39 439 39 39nn mer RuPPh33Cl3 l l A u u A A u u u u 4 mer Luuuuruu mu 1 l l 1 l 9 14 Crystal Field Theory Crystal Field Theory is a simple yet surprisingly effective model for understanding the bonding and associated electronic and magnetic properties of transition metal complexes The presence of partially lled d orbitals leads to properties of transition metal complexes not normally observed in main group compounds Among these are pararnagnetism visible absorption spectra and irregular structural and thermodynamic properties A word of caution Crystal Field Theory is simply a model and not a realistic description of bonding in transition metal complexes Consider a free gaseous metal ion M39 with a single d electron In the absence of any perturbation the 5 d orbitals are degenerate that is they are of equal energy Therefore there is an equal probability of the electron being in any of the ve orbitals Now suppose a spherically symmetric shell of negative charge approaches the metal ion The orbitals will be destabilized that is raised in energy However because there is spherically symmetric distribution of charge they will all be destabilized equally However in an octahedral complex the charge is not distributed symmetrically but rather we can assume that they constitute a set of point charges approaching from the vertices of an octahedron Now the effect on the ve d orbitals is not the same Those orbitals which have lobes pointing directly toward the vertices of the octahedron will be destabilized Since the distribution of the charge does not alter the total energy the remaining orbitals those not pointing directly toward the comers of the octahedron will be stabilized 1915 XY The metal ion now has two kinds of d orbitals In an octahedral ligand eld the dxy dXZ and dyz orbitals are known collectively as the t2g orbitals while the C122 and dxzyz orbitals are referred to as the eg orbitals The splitting between the tzg and eg orbitals is referred to as A0 where the 0 stands for octahedral or lODq The magnitude of this splitting depends on several factors that we will address shortly 1916 The center of gravity of the ligands known as the baricenter is maintained In other words the sum of the energies of the tzg and eg orbitals relative to the baricenter is 0 2x6 Dq3x4Dq0 35 A0 6 Dq l baricenter I A A0 10 Dq l 25 A0 4 Dq l L 29 II I Metal ion in octahedral field 1 I Metal ion in spherically d Fr ee metal ion symmetric field 1917 The splitting of the d orbitals will depend on the arrangement of the ligands around the metal center In general the splitting observed for square planar and tetrahedral ligand arrangements will dilTer from that of an octahedral arrangement A square planar ligand arrangement J 2 2 can be obtained from an octahedral x 39 X 39 Y ligand arrangement by withdrawing the ligands along the zaxis This should x give us a clue as to the appropriate 6 quotr A splitting pattern in a square planar 9 xx 1 ligand eld Orbitals which have lobal T xx density along the z axis will be quot dxy stabilized while those having lobal 3s density along the x and y axes will be Ao xxquot xx destabilized The result is the splitting l diagram shown T29 lt N dzz dyz dxz octahedral Tefragonally square dis ror red planar octahedral Now consider what happens when the ligands approach the metal from the vertices of a tetrahedron Now the dxy dXZ and dyz orbitals are destabilized while the dzz and dxzyz orbitals are stabilized Therefore the tetrahedral splitting pattem is the exact opposite of the octahedral splitting pattern The orbitals which were labeled t2g in the octahedral case are labeled t2 in the tetrahedral case and the eg orbitals in an octahedral ligand eld are e orbitals in a tetrahedral ligand eld because a tetrahedron lacls a center of symmetry The splitting between the e and t2 orbital sets is also referred to as A but is designated as At where the t represents tetrahedral For the same metal ligands and metalligand distance A 1 it can be shown that At 49 A l 1918 Crystal Field Theory allows us to explain many properties which ale unique to transition metal complexes Spectral and magnetic properties are use ll in characterizing coordination complexes Magnetic Properties of Transition Metal Complexes For any paramagnetic species the most fundamental question is how many unpaired electrons are there Our discussion of orbital splitting patterns is the fust step in addressing this question Hund s First Rule If a set of n or fewer electrons n occupy a set of n degenerate orbitals the electrons will spread themselves out among the orbitals to give n unpaired spins Electron pain39ng is energetically unfavorable Furthermore if two electrons are forced into the same orbital there is an additional unfavorable energy contribution because of e39 e e39 repulsions Consider a hypothetical molecule with two electrons and two orbitals separated in energy by AE We can consider two likely orbital occupations a and b Whether the system adopts con guration a or b depends only on the relative magnitudes of AE and P If AE lt P a will have the lower total energy and will correspond to the ground state but if AE gt P b will have the lower total energy and will correspond to the ground state a b 1 1 in EEOEOAE E2EOP 2EO AE E0 0 We can use the same type of argument for octahedral complexes using the appropriate dorbital splitting pattem For 1 d1 d2 d3 d8 d9 and d10 ions there is no question as to the orbital occupation However for the d4 d5 d6 and d7 con gurations two possibilities eXistand the question of which represents the lower N energy state can be answered by comparing A0 with the average pairing energy F We can calculate the energy of each con guration in terms of A0 and P relative to the baricenter Keep in mind that the t2g orbitals are 04Ao relative to the baricenter and the eg orbitals are 06Ao relative to the baricenter Therefore each electron in a tzg orbital contributes are 04A0 to the total energy while each electron in a eg orbital contributes 06A0 to the total energy Each pair of electrons in the same orbital contributes P to the total energy Ehigh spin Elow spin d4 706A0 716A0 P d5 0 72A0 2 P d6 704A0 P 724A0 3 P d7 708A02P 718A03P From any of the cases we may nd the conditions under which the two con gurations have the same energy The simplest case is d5 however the result is identical for any d electron count E11 2Ao 0 Elms 2A0 2P A0 P 1920 Therefore the spin state of any ion in an octahedral ligand eld depends only on whether the magnitude of the eld as measured by A0 is greater than or less than the pairing energy P for that ion Ion gt P we have a low spin complex Ion lt P we have a high spin complex spin state Con guration Ion P Ligands A0 predicted observed d4 Cr 23500 6 H20 13900 high high Mn 28000 6 H20 21000 high high d5 Mn 25500 6 H20 7800 high high Fe 30000 6 H20 13700 high high 6 H20 10400 high high Fe 2 17 600 d6 6 CN 33000 low low 6 F 13000 high high Co3 21 000 6 NH3 23000 low low d7 Colt 22500 6 H20 9300 high high EI giesincnr1 8359 curl 1 klhiol high spin low spin Tetrahedral Complexes 1 The same reasoning applies to tetrahedral complexes For d1 J39Ld 3T d2 d7 d8 d9 and d10 ions only one con guration is possible For d3 d4 d5 and d6 ions both high and low spin states are possible in principle and a low spin state would be expected if t 1 1 T At gt P However keep in mind that At 49 A0 all else being the same In reality At is almost never greater than P so low d4 d4 spin tetrahedral complexes are exceedingly rare 1 f f t LL lLll d5 d5 LL 1 T LLL LLLL d 6 d 6 Square Planar Complexes 1921 Low spin d8 states are not possible in octahedral T complexes but tetragonal distortion of an octahedral complex may cause suf cient splitting of the eg orbitals so that the splitting exceeds the pairing l energy Now the two highest energy d orbitals are no longer degenerate and separated by some energy dzz dzz Q In this case we can have either high spin or low l i spin complexes depending on the relative magnitudes ley d Xy of Q and P If Q gt P we have a low spin complex dyz dxz dyz dxz high low If Q lt P we have a high spin complex Sp in Spi n P gt Q P lt Q In the case of extreme tetragonal distortion we have the splitting diagram for a square planar complex Due to the large separation of the two highest orbitals and the relatively small pairing energies of real d8 ions e g RhI IrI NiH Ptu Pd1 and Aum the high spin con guration is impossible to obtain Therefore all square planar 18 complexes are diamagnetic Factors In uencing Crystal Field Splittings A The d orbital splittings depend on several factors including the identity of the metal its oxidation state the number of ligands and their geometry and nally d X the identity of the ligands 1 Identity of the metal A values for corresponding complexes of metal 22 ii ions in the same group and in the same oxidations state increase by about 40 to 50 on going from the rst to the second transition series and by about 20 to 25 from the second to the third transition series This trend is illustrated for the hexaammine complexes of the group 9 d yz d X Z metals in the 3 oxidation state There are two important consequences for complexes of the second and third transition series First these complexes o en Complex A0 have A values greater than the pairing energy so CONH363 23 000 cmrr these complexes are nearly always low spin Secondly because the splittings are so large mhmHQ F 34 000 cmil absorption bands o en occur in the UV making IrNH3 63 41000 cm l these complexes colorless 1922 2 Oxidation state of the metal A values increase with increasing oxidation state of the metal all else being the same For example A0 values of complexes of the rst transition series are about 7500 to 14000 cm391 for divalent 2 ions while those for trivalent 3 ions are about 14000 to 25000 cm39l E The number and geometry of the ligands The number of ligands in uence the magnitude of the crystal eld splitting In general a larger number of ligands leads to a greater splitting As we have already noted a tetrahedral ligand eld results in a splitting of only 49 that of an octahedral ligand eld However we must be care ll because there is also a geometric factor More relevant is the fact that a cubic ligand eld leads to twice the splitting of a tetrahedral ligand eld all else equal 4 Identity of the ligands The dependence of A values on the identity of the ligands follows a regular order known as the Spectrochemical Series This series is based on data for metal ions in common oxidation states and sometimes the order may not be consistent for unusual oxidation states Even in cases of metal ions in common oxidation states inversions of the orders of adjacent or nearly adjacent ligands may occur The Spectrochemical Series The size of the splitting depends on the nature of the ligands surrounding the metal center Ligands with large concentrations of electronic charge lead to large splittings large A values while those with lower charge densities lead to smaller splittings Additionally we can consider the ability of a ligand to be either a 139Idonor or 11 acceptor ligand Ligands which can serve as ndonors tend to cause smaller splittings while those that can serve as nacceptors cause large splittings I39 lt Br lt SZ39 ltSCN39 S bonded lt Cl39 lt NO339 lt F39 lt OH39 lt oxalate C2042 ltHZO ltNCS39 N bonded lt CH3CN ltpy lt NH3 lt en lt bpy lt phen lt N N bonded lt phosphines lt CN39 lt CO Ligands near the beginning of the series cause smaller splittings than those near the end As we shall see in addition to having important consequences for the magnetic properties of complexes ligands also in uence their spectral properties 19 23 Crystal Field Stabililztinn Energy Recall that m an octahedral hgand eld me is 69 a em sableaeomplexwmbe Thxshas important consequences for hydranon enthalpies andlamce enthalpies Hydrsz Emhalpies associated mm the following gana39ahzed equanon Mquot g 6 H20 1 MHzOsz aq Values may be calculaeedusmg hen the CPSE for each ion 15 subtracted from the actual hydration enthalpy they all fall on the same curve Spine Structures Recall that spinels are mixed oxides of the general formula le M32 02394 In a normal spinel all of 2 ions occupy tetrahedral holes while the 3 ions occupy octahedral holes In an inverse spinel the 2 ions occupy octahedral holes while half of the 3 ions occupy tetrahedral holes and the half octahedral holes We can rationalize some of the spinel structures by considering the CFSE of various ions Magnetite Fe3O4 adopts the inverse spinel structure while M11304 adopts the normal spinel structure High spin d5 ions exhibit 0 CFSE so there is no energetic advantage for them to occupy the octahedral holes where splittings and therefore CFSEs will be larger Therefore in Mn3O4 the Mn ions will preferentially occupy the octahedral holes where there is larger CFSE giving rise to the normal spinel In Fe3O4 the Fezl ions will preferentially occupy octahedral holes giving the inverse spinel structure More on Magnetic Properties How do we determine the number of unpaired electrons 1924 Fez Fe3 Mn2 Mn3 All paramagnetic species are attracted by a magnetic eld while diarnagnetic ones are weakly repelled The pararnagnetism of a substance containing unpaired electrons receives a contribution from the orbital motion of the unpaired electrons as well as from its their spins O en for lighter substances the spin contribution is predominant and we can neglect the orbital contribution The magnetic susceptibility of a substance is a measure of the force exerted by a magnetic eld on a unit mass of the specimen This quantity is related to the number of unpaired electrons per unit mass and therefore per mole of the substance We can measure XM the magnetic susceptibility per mole and correct it for diamagnetic effects which are always present to get XMcoquot the corrected molar magnetic susceptibility Corr XM can be correlated with u the magnetic moment it 284 lxjjrrT From quantum theory it can be shown that the magnetic moment due to the spins of n unpaired electrons is given by ugJSltSD where S the sum of the spins of the unpaired electrons S n x 12 and g is the gyromagnetic ratio for a free electron 20023 19 25 Eleemmie Ahsnrptinn Spectrnscnpy Consider an octahedral comp ex manx amp m the form of ale speci cally viable hgqt The mag of a a photon is ngm by the produet ofPlannk39s Constant 6 626 x 10W 5 audits frequmcy 7 115 A In genemlwhmh 1tpasses through a solunon1tsmtansnyxs I I dammshed The mm of the mtenslty of the transmitted hgqt I to the gt gt Ehv mtmslrty of the madehthgqt a is the hensmmanee T T 110 A 1 The absorbanceA sthenegame log othe tunsmmance I 710 Trlo 7 A g 310 19 26 absorblng medlum A Ebc where 6 molar absol391tvlty fl emquot mlengm oncentxanon of absorblng specles M Ifwe plot the absorbance of a substance as a funenon sh e absorption speeaum of maize 1 Two features a are important the wavelength or frequency of me 300 10500700 l I l l 1n ths slmple d ease we ean look at the Energy where 30 25 20 ls 1 Frequency curl l0 A Ml Tlalzom39 ls about 20000 emquot When agvmlon has more d eleeaons me smaaoms more compllcated llght are absorbed 1n the ease of Tlalzomz nearly all ofthe vlslble 031 400700 nm ls h orb aansmmeol ande soluaon appears vlolet e human eye also uallz es complemener colors m eolomslon mdpacaves amlxture of two the sample Wlll have the eomplemen eol or 7 K nm 400 nm 580 nm 560 um 490 nm 1927 The absorption band for TiH2053 is very weak with a molar absorptiVity of about 5 M391 cm39 1 Frequently electronic transitions that are allowed have molar absorptiVities of 104 to 105 M 391 cm39 1 This suggests that the transition in TiH2053 is somehow forbidden For an electron transition to be allowed in a system that has a center of symmetry it is necessary but not sufficient that the electron move from a g orbital to a u orbital or Vice versa This is known as the LaPorte Selection Rule The t2g and eg orbitals are all g so such a transition is forbidden All dd transitions in symmetric octahedral complexes are forbidden so the colors of these complexes in solution are fairly pale In tetrahedral systems there is no center of symmetry and so the LaPorte Selection Rule does not apply although dd transitions are still forbidden by the orbital selection rule Solutions of tetrahedral complexes are frequently much more intensely colored than those of octahedral complexes cdeotr M 6 04 2 6H20 palepink chepbue 1928 Molecular Orbital Theory Crystal Field Theory is in many ways incomplete although it does account nicely for the splitting pattems observed in the d orbitals of transition metal complexes However Molecular Orbital theory offers a more complete picture We will consider an octahedral complex MXG where each ligand has only a O orbital to be used in metal ligand bonding The can make a linear combination of the six 0 orbitals to give a set of 6 group orbitals each of these group orbitals has the appropriate symmetry to overlap with a metal s p or d atomic orbital resulting in a total of 6 bonding and 6 antibonding molecular orbitals Three of the metal d orbitals tzg do not have the proper symmetry to mix with any of the group orbitals so these will be nonbonding with respect to metalligand O bonding Three bonding and three antibonding molecular orbitals derived from the metal p orbitals and the appropriate group orbitals are degenerate and these are denoted t1 and tluquot Two bonding and two antibonding molecular orbitals derived from the metal 122 and dxzyz orbitals and the appropriate group orbitals are degenerate and these are denoted eg and egquot Finally the s atomic orbital and the appropriate group orbital give rise to a nondegenerate bonding and antibonding molecular orbital denoted a1g and algquot wig 2 4mu4 4r y gen 4 3 These mteramons result m the MO dAagrams shown below 19 30 LAL M39T hvvh r mm that they are aemauy anurbondmg thh respect to mexahhgard Orbondmg Ihrs explarhs why These 1r mbxtzls may overlap wnh the d oh or dy metal ormals as shown Now instead of bohdmg 53L he and 13 1V 9 v I E quot 6 6 Theposmons ofrher1S and a orbxtals m the MO diagam are vanable There are two important eases to eohsrder Case 1 The hgahdrs an dohor Examplesmdude x H20 OH39 and omerhgahds near 111 11 and em g orbxtals the effects erase the margy ofthemetal as ormah and deerease the ds sphmng between her1S and e orbxtals A nedohorhgah aretherefore weak eld hgands A m the absence uf v i n merac n3 3d 9ng Case 2 The ligand is a nacceptor Examples include CO CN39 and phosphines In this 1931 case the ligand TI orbitals are vacant 139 molecular orbitals The effect of their interaction with the metal tzg orbitals is to decrease the energy of the metal tzg and increase the splitting between the t2g and egquot orbitals A Therefore TI acceptor ligands are strong eld ligands x quot399 1 39 T29 A in The absence of 11 inferag rions I 61 Chapter 6 Inorganic Thermodynamics Thermodynamics is the branch of chemistry and physics that deals with the relationship between heat and other types of energy during the course of chemical and physical processes Some definitions to keep in mind System Surroundings Universe State Phase Internal Energy U Heat q Work w State Function that collection of matter upon which we choose to focus our attention anything in thermal andor mechanical contact with the system This implies that energy in the form of heat or work may be transferred between the system and its surroundings the system the surroundings a description of a system in terms of properties which do not change with time Properties may include temperature volume pressure etc a description of the physical form of a substance as a solid liquid or gas The sum of the kinetic and potential energies of the particles making up a system a form of energy which ows spontaneously from a warmer object to a cooler one the energy exchange resulting when a force F moves an object through a distance d wFd A property whose value depends only on the current state of the system and not how the system got to that state U P V T are all state lnctions q and w are not path independent and are therefore not state lnctions They may be referred to as path functions The First Law of Thermodynamics The First Law of Thermodynamics may be stated in a number of ways Basically it is a statement that energy may be neither created nor destroyed but rather is conserved The total energy of the universe is conserved Umiv Usys UsuIT a constant AUuniv 0 96 Ausy 7AUsm Thermodynamic Sign Convention Surroundings AUsys AU AUuniV 0 62 qgt0 gt qltolt System WgtO gt WltO Heat q is positive when it ows from the surroundings into the system Work is positive when the surroundings do work on the system The change in intemal energy of the system AU is given by the sum of the heat absorbed by the system q and the work done on the system w AUqw This last equation is also a statement of the First Law Enthalpy and Enthalpy Changes The heat absorbed or evolved by a reaction depends on the conditions under which the reaction occurs If a reaction occurs under conditions of constant pressure the heat of the reaction is designated qp where the subscript p indicates constant pressure The heat of reaction at constant pressure qp is related to a property of the reactants and products called enthalpy H Like U P V and T H is a state lnction Enthalpy H ls another thermodynamlc pmme of a system H U PV WhereUls the mtemal energy ofthe system Plslts pressure andVls lts volume by the heat lt absorbs or evolves That ls AH up ev ry me we vvantto know AH for a reaeuon Beeause Hess39 Lavv ls sueh apowel39ful tool lt ls only neeessary to tabulate AH values for a llmltednumber ofreacuons These values along vvl Hess39 Lavv wlll allow us to eompute AH values for a Wlde vanety ofreaeuons The reaeuons for reaeuon ls then gven by A3 I n AH pudum I m AE muunu Spontaneous Proeesses A spontaneous proeess ls one that gven sumnent ume wlll oeeur by ltself vnthout any eonunulng extem lntervenuon All proeesses whether physlcal or hemlcal have aprmerred 6411an For example a boulder rolls downhlll rather than up hull and a pleee oflron lat outslde m m lst alr wlll spontaneously reaet Wth q atmosphere produee Fe2 3 rust The rust does not spontaneou y d eompose to non and q 2 Fe 5 32 q 9 F220 5 spontaneous F220 5 e 2 Fe 5 32 q 9 nonrmontaneous ofaprocess 64 In order to determine whether a given process is spontaneous we must invoke the Second Law of Thermodynamics which is expressed in terms of the thermodynamic quantity entropy Entropy Entropy S is a measure of the randomness or disorder of a system or its surroundings Like internal energy U and enthalpy H entropy is a state function Entropy and the Third Law of Thermodynamics The Third Law of Thermodynamics states that the entropy of a perfect crystalline substance at 0 K is 0 In general as the temperature of a substance is increased its entropy increases The accompanying gure shows how the entropy of a substance varies with temperature Entropy increases gradually with temperature but jumps abruptly when a phase change occurs The standard or absolute entropy of a substance 8quot is the entropy of the species in its standard state The Standard entropy 8 JK Gas 50 Entropy of vaporization 40 W 6 30 Entropy of fusion 0 50 100 150 200 250 300 350 Temperature K standard state of a substance is the pure substance at a pressure of 1 bar approximately 1 atm For species in solution the concentration is 1 M The table on the next page gives the standard entropies of a variety of substances Note that unlike standard enthalpies of formation the standard entropy of an element in its reference state is nonzero Standard Entropies at 25 C 8 8 8 Formula Jmol oK Formula Jmol oK Formula Jmol oK Hydrogen Carbon continued Sulfur Haq 0 0520 1510 829 2281 H2g 1306 HCNg 2017 Srhombic 319 Sodium HCNI 1128 Smonoclinic 326 Naaq 602 0049 3097 8029 2481 Nas 514 00141 2144 81259 2056 NaCls 721 CHscHOg 266 Fluorine NaHCOss 102 cszoHa 161 F39aq 96 Na2003s 139 Silicon F2g 2027 Calcium 515 180 HFg 1737 Ca2aq 552 Si02s 415 We Cas 416 SiF4g 285 craq 551 05105 382 Lead 0129 2230 CaCOss 929 Pbs 648 HClg 1868 Carbon PbOs 665 Bromine Cgraphite 57 PbSs 913 Braq 807 Cdiamond 24 Nitrogen BFZU 1522 009 1975 N2g 1915 Iodine 0029 2137 NH3g 193 l39aq 1094 HCOs39aq 950 NOg 2106 125 1161 01149 1861 N02g 2399 Silver 04149 2192 HN03aq 146 Agaq 739 04169 2295 Oxygen Ags 427 061160 1728 029 2050 AgFs 84 HCHOg 219 039 2388 AgCls 961 CH30HI 127 OH39aq 105 AgBrs 1071 0829 2378 11209 1887 Agls 114 H200 699 Some General Observations l S solid lt S liquid lt S gas Ballpark molar entropy 8quot values Solid z 0 90 J K391 mol391 Liquid z 50 150 J K391 mol391 Gas z 130 a J K391 mol391 NOW H and AH Values 2 usually given in M or 1d mol l while s and As values are usually givenin J K3910r J K391 mol39l 2 S simple molecule lt S complex molecule S H2g s 1306 J K391 mol391 S CC4g s 3097 J K391 mol391 3 S increases as the temperature of a substance increases S Cu s 200K 237 J K391 mol391 S Cu s 300K 333 J K391 mol391 Tables of S0 values can be used to nd ASm AS Z S pr0ducts Z S reactants just as AH data is used to calculate AH r m Example What is the entropy change associated with the following reaction at a pressure of 1 atm and a temperature of 25 C 2 H2 g t 02 g a 2 H20 1 66 67 The Second Law of Thermodynamics The Second Law of Thermodynamics states that in any spontaneous process the entropy of the universe that is the entropy of the system plus the entropy of its surroundings increases Stated mathematically AS Assys Assun gt 0 Note that the Second Law states that the criterion for a spontaneous process is an increase in the entropy of the universe not of the system or surroundings There are many examples of spontaneous processes that involve a decrease in the entropy of the system but these are invariably accompanied by a larger increase in the entropy of the surroundings Similarly many spontaneous processes involve a decrease in the entropy of the surroundings but these must be accompanied by an even larger increase in the entropy of the system Any process leading to a decrease in the entropy of the universe is forbidden but its exact reverse will lead to an increase in the entropy of the universe and is therefore spontaneous What happens if for a particular process ASu 0 If ASu 0 there is no driving force for either the forward process or its reverse and the process is at equilibrium A process involves a change in the system AND its surroundings and can go in one direction only The sign of ASu detennines whether the process will go For aprocess A a B if ASu gt 0 the process will go if ASu lt 0 the process will not go but B a Awill go if ASu 0 the process is at equilibrium The sign of ASu tells us whether a process will go It says absolutely nothing about how fast it will go For example C diamond a C graphite is a spontaneous process at 25 C and 1 atm but occurs so slowly that we could never even begin to see a change Thermodynamics tells us whether a process will go and if so how far Kinetics tells us how fast 68 We already know how to calculate the entropy change for the system during the course of a chemical reaction but how do we determine the change in the entropy of the surroundings so we can calculate the entropy change of the universe The entropy change of the surroundings is related to the amount of heat that ows between the system and its surroundings In general AS all where q is the amount of heat absorbed by the system from its surroundings and T is the absolute temperature For an exothermic process q lt 0 so the entropy of the surroundings increases while for an endothermic process q gt 0 so the entropy of the surroundings decreases Now we can restate the Second Law in terms of ASsys q and T We ll drop the sys subscript and assume that a quantity without an explicit subscript refers to the system As AS 1 gt o 139 Keep in mind however that for a constant pressure process qp AH so AS As if gt o If we multiply through by i T 39139AS 39139AS An lt 0 or AK 39TAS lt 0 Now we can see that the spontaneity criterion can be expressed exclusively in terms of the absolute temperature and changes in properties of the system AH and AS This suggests the invention of still another thermodynamic quantity 69 GIBBS FREE ENERGY G The Gibbs Free Energy G is de ned by the equation by the G H 7 TS The change in G is given by AG AH ATS However for constant temperature processes ATS TAS so at constant temperature AG AH 7 TAS Therefore the sign of AG serves as the criterion for the spontaneity of a reaction If ASu gt 0 AG lt 0 process is spontaneous ASu lt 0 AG gt 0 exact reverse process is spontaneous ASu 0 AG 0 process is at equilibrium Standard Free Energy Changes As we have seen before we de ne a standard state for the purpose of tabulating thermodynamic data For liquids and solids the standard state is the pure substance at a pressure of 1 bar 1 atm for gases the gas at a partial pressure of 1 bar and for solutes l M concentration under a pressure of 1 bar We can calculate standard free energy changes AGO for reactions in either of two ways If we know AHquot AS0 and the temperature we can use the relationship AGO AHO TASquot Example What is the standard free energy change for the reaction of 2 moles of H2 g with 1 mole of 02 g to form 2 moles of H20 1 at 25 C We have already calculated ASOfor this reaction ASO 3264 J 39K391 Standard Free Energy of Formation 610 The standard free energy of formation AG f of a substance is de ned in a manner similar to the standard enthalpy of formation The standard free energy of formation is the free energy change associated with the reaction in which one mole of a substance in its standard state is formed from its elements in their reference states at a pressure of 1 bar 1 atrn and any speci ed temperature Standard free energy changes for reactions can be calculated from tabulated values of the standard free energies of formation of all the reactants and products in exactly the same manner as standard enthalpies of reactions are from standard enthalpies of formation As with standard enthalpies of formation the standard free energy of formation of an element in its reference state is zero AGO Z n AG products 2 m AG reactants Standard Free Energies of Formation at 25 C AGors AG rs Formula kJmol Formula kJmol He dmgequot Carbon continued 2 8 CzH4g 684 20dium CzHeg 329 C H 1245 Naaq 261 9 Hagen 1 10 Nas 0 CH OH NaCKs 3840 0339 0 122 NaHCOgS 851 9 032 1820036 10481 Holley 12g 6 Calcium Ca2aq 5530 33 113 7 C 4 0223 5035 COW 686 gacgas 11288 305329 ar on 2 5 Cgraphite 0 Silicon Cdiamond 29 31 856 5 c309 1372 I 2 S 0029 3944 SiF4g 1506 HCOsTaQ 5871 CHM 508 AG AG p Formula kJmol Formula kJmol Lead Fluorine Pbs 0 Nat 2765 PbOs 1892 59 0 PbSs 967 HFg 275 Nitrogen Chlorine N2g 0 C39aq 1312 NH3g 16 C2g 0 NOg 8660 HCg 953 N02g 51 Bromine HN03aq 1105 Br39aq 1028 Oxygen BrzU 0 029 0 Iodine 03g 163 I aq 517 OH39aq 1573 2s 0 H209 2285 Silver H200 2372 Agaq 771 Sulfur Ags 0 32g 801 AgFs 185 Srhombic 0 AgCIs 1097 Smonoclinic 010 AgBrs 959 3029 3002 Ags 663 H2 Sg 33 611 612 Free Energy Changes During A Reaction A chemical reaction proceeds until a state of equilibrium is reached The driving force for this or any other reaction is a decrease in free energy The equilibrium composition of the system is that with the minimum free energy Ifyou look at the gure to the right you will see that the reaction of gasoline with 02 to produce H20 and C02 is highly exergonic that is AG0 has a large negative value As the reaction proceeds the free energy of the Reactants Products system decreases until a state of QaSOIine and 02 CO2 and H20 equilibrium is reached Any further reaction would require the free energy of the system to increase In general the more negative the value of AG the greater the value of the equilibrium constant and the farther the reaction will proceed before equilibrium is achieved Spontaneous reaction AG Free energy gt Equilibrium Let s now consider a reaction with a large positive value of AG According to the gure we should expect this reaction to proceed only to a small degree before equilibrium is reached As you might guess N nsp mane US there is a relationship between the value of gt readlon Ago AG0 and the equilibrium constant which we E will investigate next g L ltEquilibrium Reactants Products Relating AG0 to the Equilibrium Constant The thermodynamic equilibrium constant K is the equilibrium constant expression in which concentrations of gases are expressed in terms of their partial pressures in atmospheres and the concentrations of solutes in liquid solutions are expressed in terms of molarities In reality the thermodynamic equilibrium constant is expressed in terms of the activities of the substances taking part in the reaction Partial pressures and concentrations are merely approximations to the activities of substances 613 Under standard conditions unit concentration or partial pressure AGO for a reaction can be calculated from data found in thermodynamic tables as was previously illustrated When reactants andor products are not at unit concentrationpressure the following equation allows us to calculate AG AG AGO RT 1n Q where Q is the thermodynamic reaction quotient R is the gas constant 8314 J 39 K391 39 mol39l and T is the absolute temperature When a reaction has reached equilibrium there is no driving force for the reaction in either direction so AG 0 and the concentrations and or pressures in Q are the equilibrium concentrations andor pressures so Q K We can substitute these values into the previous equation 0 AGO RT In K and rearrange to obtain the relationship between AG0 and K that we alluded to in the previous section AGO RTan Note that the units of R are J 39 K391 39 mol391 while AG0 is normally expressed in 1d Before using this equation is used we must express these both either in terms of J or 1d Changes in AG with Temperature The thermodynamic tables in your book as well as most thermodynamic tables you might expect to see apply to a temperature of 25 C Nothing in the de nition of standard state refers to this speci c temperature however It is just that most of the data have been tabulated at this temperature While the temperature dependence of G and AG are explicit in their definitions G H TS and AG AH TAS the temperature dependence of AH and AS are not so obvious There are methods for determining values of AH0 and AS0 from data tabulated at 25 C but we will not concem ourselves with them Instead we will note that as long as the temperature changes are not too large AH0 and AS0 may be assumed to be constant with respect to temperature so that AG T z AH398 TASg98 As we have previously noted a negative value of AG indicates a spontaneous reaction and AGT z AH298 TAS298 614 so the signs of AH and AS will provide insight as to whether a reaction will become more or less favorable with increasing temperature Since both AH and AS can be either positive or negative there are four possible combinations of the signs of AH and AS Sign of AH Sign of AS Sign ofAG negative positive negative at all temperatures negative at low temperatures negative negative pos1t1ve at high temperatures positive at low temperatures pos1t1ve pos1t1ve negative at high temperatures positive negative positive at all temperatures You can verify that these conclusions regarding the sign of AG are correct For example when AH is negative and AS is positive we are subtracting a positive value TA S from a negative value AH to obtain AG The diiTerence is always negative irrespective of the temperature However when both AH and AS are negative the results will diiTer depending on whether the temperature is relatively low or high At suf ciently low temperature lAHl gt lTAS l so we are subtracting a less negative value from a more negative value resulting in a diiTerence which is negative However at suf ciently high temperature lAHl lt lTAS l so we are subtracting a more negative value from a less negative value resulting in a diiTerence which is positive We should note that the terms low temperature and high temperature are relative descriptions Relating AG0 to the Equilibrium Constant The thermodynamic equilibrium constant K is the equilibrium constant expression in which concentrations of gases are expressed in terms of their partial pressures in atmospheres and the concentrations of solutes in liquid solutions are expressed in terms of molarities In reality the thermodynamic equilibrium constant is expressed in terms of the activities of the substances taking part in the reaction Partial pressures and concentrations are merely approximations to the activities of substances 6 1 5 Under standard conditions unit concentration or partial pressure AG for a reaction can be calculated from data found in thermodynamic tables as was previously illustrated When reactants andor products are not at unit concentrationpressure the following equation allows us to calculate AG AG AG RT 1n Q where Q is the thermodynamic reaction quotient R is the gas constant 8314 J 39 K391 39 mol39l and T is the absolute temperature When a reaction has reached equilibrium there is no driving force for the reaction in either direction so AG 0 and the concentrations and or pressures in Q are the equilibrium concentrations andor pressures so Q K We can substitute these values into the previous equation 0 AG RTan and rearrange to obtain the relationship between AG and K that we alluded to in the previous section AG 7 RT In K Note that the units of R are J 39 K391 39 mol391 while AG is normally expressed in 1d Before using this equation is used we must express these both either in terms of J or 1d Example Silver oxide decomposes to silver and dioxygen according to the following equation 2 Agzo S v 4 Ag S 02 g At 25 C AH 621kJ and AS 1327 J 39K39l Calculate AG and K for the reaction at 25 C and at 225 C 616 Notice that AGO went from a positive value at the lower temperature to a negative value at the higher temperature in accord with out prediction from the table above We can in fact predict the temperature at which AGO goes from positive to negative Of course the temperature below which AG0 is positive and above which AG0 is negative is the temperature at which AGOequals zero We can solve for this temperature by setting AGO equal to zero in the equation AGO AHO TASquot 0 We should note that this calculation is only approximate because of the assumptions we made regarding the constancy of the values of AH0 and AS In general these values will change with temperature Energetics of Ionic Bonding According to Coulomb s Law the electrostatic force between two charged pa1ticles is given by F A 4 I so 1 where 60 8854 X 10 3912 C2 39 J391 39 m391 permittivity offree space q and q are the charges in C d is the distance between the particles in m The corresponding electrostatic energy is amp 4121 account the meeramons between many was sxmultaneously For Examplem the NaCl 1amee there are 6 cr was surroundmg a Na m at admance onquot 2 Na ms at adASmee of2 Wequot 8 c139 dutance 31 6 Na ms at a dutance of 2 etc a we have an m mte senes of 939 L g Annywk mum mummy mam Wm m 1 meme my m 1 1154 1115an 1 m am we nan quotcum WWW 1m Sumng m m m m quotemu quotmg st m emhl nail m 39 The value 15 called me Madelung con ant A Lamee A NaCl 1 74756 CsCl 1 76276 Car2 uonte 2 5194 A120 4 1719 A few others are gven m Table 6 4 Sowe can gvethe amenve energy ofmeeramon for amole ofa subsLance as NAVAx z39 7 Azend 5 m u h continually decrease as d e 0 618 However ions are not point charges As d becomes smaller and smaller we must consider the fact that at very short distances their electron clouds interact repulsively This repulsive term operates only at extremely small distances Eu dl where n is referred to as the Born exponent values range from 5 to 12 and depend on the electron con gurations of the ions Taking into account the attractive and repulsive terms we have ENMA 239 e 1l 41 2 n Lattice Enthalpy U We de ne the lattice enthalpy of an ionic compound as the energy necessary to convert 1 mol of the solid into its gaseous ions MmXX s a m M g X X g AH U This is the opposite convention to what the text uses BomLande Equation N A z z39 e2 1 U a 1 4 I so to n e39 con g of ion n He 5 Ne 7 Ar 9 Kr 10 Xe 12 Rolling all the constants into a single constant 1339 2105 gt A 1 z39 Mfrr 619 BomMayer Equation Both of these equations require knowledge regarding the crystal lattice However AF Kapustinskii discovered that if the Madelung Constant for a variety of crystal structures was divided by the number of ions in the formula unit a relatively constant value is obtained Lattice v A Av NaCl 2 174756 0873780 CaF2 3 25194 083980 A1203 5 41719 083438 He proposed a hypothetical rock salt N aCl lattice energetically equivalent to any ionic solid making it possible to calculate U without knowing the details of the lattice This equation is known as the Kapustinskii Equation 1202 1105 Ir11quotquot v z z39 Il 0 The extent to which the equations provide agreement with experimental values tells us how appropriate the ionic model is for a particular compound There is o en a signi cant diiTerence between calculated and measured values of U when there is signi cant covalence in a compound Formation of Ionic Compounds Direct experimental measurement of lattice enthalpies is dif cult Some degree of ionpairing always occurs so it is not possible to vaporize the solid completely into isolated ions However whenever we have a process for which an enthalpy change is dif cult to measure it is o en possible to use other data in conjunction with Hess Law to determine the enthalpy change for the process of interest BomHaber Cycle 620 The BomHaber cycle is based on Hess Law We have a process for which it is difficult to directly measure AH However if we can write the process as a sum of other reactions we can calculate AH from the AH values of the other reactions In the formation of Li20s from its elements Lis and 02 g we consider 5 processes 1 Atomization of Lis AH for the atomization of one mole of Lis is 162 k 2 Dissociation of 02 3 Ionization of Li 4 Formation of 0239 2Lis a 2Lig AH324kJ The 02 molecules are separated into individual atoms This requires the breaking of the 00 bond AHOO 494 ldmol 12 02 g a 0 g AH 12 AHOO 247 1d An electron is removed from each Li atom resulting in the formation of a L ion AH for this process is essentially equal to the first ionization energy of Li 520 kJmol 2 Li g a 2 Lil g 2 e39 g AH IE1 1040 k An electron is added to each 0 atom to result in a negatively charged oxide ion AH for this process is the sum of the first and second electron attachment enthalpies of O 0 g t e39 g z 0 g AH AHEA 141kJ 0 g e39 a 02 g AH 744 k 0 g 2 e39 g a 02 g AH 603 k 5 Formation of Li20s from its ions The L and 0239 ions condense to form solid LiZO AH for this process is the negative of the lattice enthalpy for LiZO since this process is the exact reverse of the process whose AH is the lattice enthalpy of LiZO 2LNg 0239g Li20s AHU 621 These ve steps can be added together to give us the equation for the formation of LiZO s from its elements in their reference states The enthalpy change for the latter process is simply the standard enthalpy of formation of LiZO s AH f 2Lis a 2Lig AH324kJ 12 02 g a 0 g AH 12 AHOO 247 1d 2 Li g a 2 L g 2 e39 g AH IE1 1040 k 0 g 2 e39 g a 0239 g AH 603 Id 2 L g 0239 g U20 8 AH U 2 Li s 12 02 g a L120 s AHfLi20 s 596 1d Therefore we can say 324 k 247 1d 1040 k 603 k U 7596 k or U324kJ247kJ1040kJ603 kJ 596 kJ2810 1d Since this is the enthalpy change per mole of LiZO s U 2810 ldmol Compa1ing this to calculated values BomeLande H39pm 1319 z 105 25194 1 2 I 11 29010 201 pm 5 m1 BomMayer 13129 x 105 M 25194 1 2 U 1 130 9 296103 201 pm 201 pm mo Kapustinskii than 1202 z 105 3 1 2 1 I 2Mz103 201 pm 201 pm m1 Graphically 2 Li9 029 622 AH603 kJ 2Li g 2equot 09 A H 1040 kJ 2 i9 09 AH 247 kJ 2 Li 9 12 029 AH324 kJ EU 5 12 02 g AHf 596 kJ U 2810 kJ Lizo S 623 We can use these cycles to rationalize the existence of certain compounds e g NaCl and the non existence of others eg NaClZ Ifwe assume the radius of a Nazl ion is similar to that of a Mgzl ion U for NaClZ is about 2650 ldmol What adjustments must be made to our cycle We can rationalize the nonexistence of NaClZ to the exceptionally large second IE of Na Ihermodynamres of sdluuon we ean assemble srmrlar eyeles for other physreal processes Conslda39 the dssdluupn of an rmre solldm mater MK 5 M39quot 3 X 3 AH AHenm We ean wnte thrs equaupn as the sum ofthree processes MXs M39gngg AHU M39quot 9 M39quot 3 AH AHMM39 Xquot 9 Xquot 3 AH AEWW39 What rs the nature othe hydrated rpnsv The nations normally have a grim hydration sphenz 0M or th arymg numbers of al 5 E E I s e E e S num er ofwatermolecules surr undmg anr h r Ion radlus pm hydrated rpn hydrated radlus pm Na 116 NaH20 276 K 152 K0120 232 hydrauon number wlll be more m uencedby the charge densrty of the rpn Consequences are lmpman For example K rms pass througn prologeal membranes more easrly than Na rdns K rms are retarnedmdre strongly on srze excluslon resrns densrues Thus whrle a smaller canon may have a smaller pnmary hydranon mhere rt may well have a larger hydranon number 625 Ions with larger charge densities also tend to have more negative hydration enthalpies Enthalpy of Solution NaC1s a Na g Cl g AH U 788 1d Na g a Na aq AH AthdNa 406 1d Cl39 g a Cl39 aq AH AthdCl39 7378 kJ NaCl s a Na aq Cl aq AH AHsolnNaCl 4 1d Entropy of Solution NaC1s a Nal g Cl39 g TAS 68 1d Na g a Na aq TAS 27 kJ Cl g a Cl aq TAS 728 kJ NaC1s a Nal aq Cl39 aq TAS 13 1d Therefore AG AH TAS 4 k e 13 1d 9 k and the formation of a 1M aqueous solution of NaCl at SATP is spontaneous Formation of Covalent Compounds We can use bond energies to estimate enthalpy changes for chemical reactions that occur in the gas phase This method applies only to gas phase reactions however Approximation AHO z 2 bond energies bonds broken 2 bond energies bonds formed 626 Consider the reaction between CH4 g and 02 g to form C02 g and H20 g 1 H c H g 2 99 g gt gc gt g 2 H g H g H In this reaction for every mole of CH4g we break 4 moles of C H bonds single and 2 moles of 00 double bonds and form 2 moles of CO double bonds and 4 moles of 0 H single bonds For obvious reasons it is use ll to write Lewis structures for all the reactants and products We can of course calculate a more accurate value for AH0 by using standard enthalpies of formation AH 2 H101 AH H20 9 t 1 H101 AH 002 g 1 H101 AH CH4 g AH 2 mol 2418 ldmol 1 mol 3935 1dmol 1 mol 749 1dmol AH 78022 k It should be pointed out that such good agreement between the estimate and the accurate value are not usually encountered and bond energies should only be used to estimate enthalpy changes when heats of formation are not available The values agree so well in part because we used the CO bond energy derived from the C02 molecule Furthermore this method of estimation should only be used for gas phase reactions Thermodynamicvs Kmenc Control ofReacnons When ammomaxs burned the thermodynamically favomdpmm s dmm39ogen 4NH3g301 2N2g6H20 4N39H3g5014NOg6HZO AG 958kJ Unwxm 51 rudv m4 Rm mum
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'