Intro Inorganic Chem
Intro Inorganic Chem CHM 218
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Chapter 12 The Alkaline Earth Metals 121 Beryllium has properties which distinguish it from the other members of the family and its chemistry is frequently discussed separately Common Features All of the allmline earth metals are silvery in color and have fairly low densities Density increases with increasing atomic number They have stronger metallic bonding than the alkali metals and as a result have higher melting points hardnesses and enthalpies of atomization The metals are less reactive than the neighboring allmli metals but increases in reactivity parallel the increase Element Density mp C mom gem 3 klmol 1 Mg 174 649 149 Ca 155 839 177 Sr 263 768 164 Ba 362 727 175 observed in the alkali metal family increasing reactivity with increasing atomic number They have high electrical and thermal conductivities which are characteristic of metals Unlike other metals however the allmline earths are so and this trend increases going down the group This so ness is the result of very weak metallic bonding There is a strong correlation between the so ness low melting point and small enthalpy of atomization All of them react with 02 Be Mg Ca and Sr give only MO Ba gives both BaO and BaOz M1202 MO Ba 02 H Ba02 Magnesium like its diagonal neighbor lithium reacts directly with N2 to yield the nitride Mg3N2 as do the heavier alkaline earths Be does not 3 M N2 M3N2 All react with halogens to give MXZ MX2MX2 Ca Sr and Ba react with cold water to give MOH2 and H2 Mg reacts only with hot water M H20 M0H2 H2 122 Ionic Compounds All of the metals form a stable 2 cation and most of the compounds are stable ionic solids colorless unless the anion imparts a color to the compound eg MnO439 CrO4239 Cr207239 Mg has a chargetovolume radius greater than that of LF so many of its compounds exhibit covalent characteristics Unlike the allmli metals salts are typically hydrated with the degree of hydration decreasing down the group Hydroxides however exhibit the opposite trendisrOH2 and BaOH2 are octahydrates while MgOH2 and CaOH2 are anhydrous Usual hydration numbers for several compounds are given in the table below M Mg Ca Sr Ba Solubility of Allmline Earth Metal Salts Compounds are typically less soluble than the corresponding alkali metal compounds Again solubility depends on AG for the process MXz S M 31 2 X 3 1 Two contributions to AG AG AH TAS Sulfates become less soluble descending the group but hydroxides become increasingly soluble This is consistent with the trend associated with cationanion size matching 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 M2 and X39 sz s M2 g 2 x g AH U M g a M aq AH AHm M 2 X39 g r 2 X39 aq AH 2 x Athd x sz s M2 aq 2 x aq AH U Athd M2 2 x Athd X39 123 In general the lattice enthalpy and the hydration enthalpy for the cation will both be larger for MX2 than for MK Additionally we have twice the hydration enthalpy for the anion for a 1 anion Comparing NaCl with MgClZ compound AHgoln TASSoln AGSOOIH MgClZ 160 34 125 NaCl 4 13 79 For M gClz enthalpy factors favor dissolution while entropy factors oppose it This is the opposite of the behavior we saw for NaCl All else being equal solubilities of ionic compounds pairing 22 ions are typically less than those pairing 2l ions MY s a M2 aq Yz39 aq AH U Athd M2 Athd YZ39 U olt L 2 239 MZVYZ39 227 2 8 MW 2 X39 3271 76 Lattice enthalpies may be 33 greater but total hydration enthalpy may not compensate Furthermore AS term is less favorable for the divalent anion The Elements um u The Fundamental Properties of Gran 2A Elements Ref 32 Hmlilum Mnunt lunl Cnlrllun Smm um n um Rndlunl Symbva Bu M u m m Amun u numhel 4 l2 2 1 5 HR NMquot mum vum 2mm 40 mm mm In 22mm AquotS Allnmdnnws Lsmm ovam umm mmn 571702 v v 2 sasuu w m ux rum m 4 Mann n u u m m am am mu m 31 mm L v 3 9 51 I n1 Sn11w 5451420 7701550 75mm vimmu Dwmlm ncm I74 i 2 MA 3 l 5 mam A m I ml 1 15 2A 1mm mums ShannuanrcwnL Au J mm mm mun 132m Mum MI I1 LU LU 0 quot0 Krdcmlly A I 17 15 I ueuunig mm quotMI harAEA V v 4 737 rm 7m 790 mm mm z v w lwnulmu mm u mm m m m 54v 1 nnmuaclcmnu m 14 51 m 9 mm um Dmnunl Ivydam W lvlrrlluu Davy Dix Davy um 1894 mm s max 1 ml law quot 1 BcO MM C440 SK 510 M0 RIO Aml v w nlmmlm unpho Wm m a Ham um Bu mm quotw 2 NM MNNJ um sh Rum lpwlulun Bax MAX aux srx1 ax rpw hydmm Nmm Mm1 auxL sxu uml mumm hm hon u an I n mnlnndmd mm quotm x mmquot mch mun pmeNmL Mhmm mm m 125 Beryllium Steel gray in color fairly hard fairly high mp but low density High electrical conductivity resistant to corrosion strong nonmagnetic Occurs as the minerals bertrandite Be4Si207OH2 and beryl Be3AIZSi6018 The latter occurs in various colors due to the presence of trace impurities for example aquamarine and emerald with CrIII The element and its compounds are extremely toxic and inhalation causes berylliosis There are two forms of berylliuminduced lung disease acute and chronic Acute berylliosis has a sudden rapid onset and is characterized by severe in ammation of the lungs pneumonitis coughing increasing breathlessness dyspnea and other associated symptoms and ndings In addition in some individuals the skin or the eyes may be affected The more common chronic form of the disease develops more slowly and in some cases may not become apparent for many years a er initial beryllium exposure Chronic berylliosis is characterized by the abnormal formation of inflammatory masses or nodules granulomas Within certain tissues and organs and Widespread scarring and thickening of deep lung tissues interstitial pulmonary brosis Although granuloma development primarily affects the lungs it may also occur Within other bodily tissues and organs such as the skin and underlying subcutaneous tissues or the liver In individuals With chronic berylliosis associated symptoms and findings often include dry coughing fatigue weight loss chest pain and increasing shortness of breath From WebMD 126 The extremely large chargetoVolume ratio 1100 Cmm3 means that Be 2 is highly polarizing and covalent character dominates the bonding Even compounds that might be expected to be simple ionic compounds are usually tetrahydrates BeC12 4 H20 is actually BeH2042 2 or The anhydrous solids are typically in nite chains with 4coordinate Be atoms X X quot39HIIIBe BeII39W39XDBe o X X X X X In the gas phase at higher temperatures Be halides are linear molecules Xi BeiX At lower temperatures but still in the gas phase 3coordinate dimers exist X X Be Be X X Be X X Although a metal it has some characteristics of nonmetals including the ability to form oxoanions Along with Al diagonal relationship and Zn Be is sometimes referred to as a weak metal near the metalsemimetal border Like Al and Zn its oxide and hydroxide are amph uteric That is they will react with acids as well as bases By comparison MgO and MgOH2 are strictly basic 1360 H20 2 H30 BeOH242 oxides BeO H20 2 OH39 a BeOH4239 BeOH2 2 H3O a BeOH242 hydroxides BeOH2 2 OH39 a BeOH4239 127 Magnesium There are some aspects of the chemistry of Mg that are suf ciently diiTerent from Ca Sr and Ba to discuss separately For example Hydrates typically decompose when heated rather than simply dehydrating MgC12 H20 a MgOHC1 HCl CaC12 2 H20 a CaCl2 2 H20 Compounds with covalent bonds are not uncommon du to the still relatively large chargetovolume radius of Mg2 120 Cmm3 vs Ca2 which is about 52 Cmm3 and comparable to L Mg reacts with alkyl halides and inserts in the CiX bond forming Grignard Reagents Like alkyl lithium compounds these are used as alkylating agents in organic chemistry RiX ether Mg s a Re MgiX ether Magnesium occurs in nature as camallite MgClZ 39 KCl 39 6 H20 and dolomite MgCO3 39 CaCO3 These are both actual stoichiometric compounds in which the indicated cations occupy holes in the lattice of the indicated anions rather than simple mixtures Mg2 occurs naturally in seawater and is the third most abundant ion a er Na and Cl39 seawater provides a major industrial source Extraction of Mg2 from seawater is accomplished by the Dow Chemical Extraction Process Mg2 ions are first precipitated as MgOH2 Ca0H2 S t Mg 211 Mg0H2 S Ca2 211 Following the ltration the MgOH2 s is dissolved in HCl MgOH2 s 2 HCl aq a MgC12 aq 2 H20 0 The solution is evaporated and the solid MgClZ is heated to melting in an electrolysis cell similar to the Downs Cell and electrolyzed MgCW Mg0Clzg 128 Maintaining an inert atmosphere above the reactive liquid Mg is problematic because unlike liquid Na Mg will react with N2 as discussed earlier SF6 or 802 are o en used to protect the Mg from atmospheric O2 and N2 Thermodynamically Mg is a potent reducing agent Mg22e39eMg E 237V but its reactivity is less than might be expected because its surface become passivated by a very thin adherent coating of MgO that protects the metal from further oxidation Mg bums in 02 with the emission of a brilliant white light Powdered Mg was used in early ash photography and disposable ash bulbs and ash cubes made use of rapid combustion of brous Mg to provide a ash 2 Mg 02 a 2 MgO Burning metals like Mg pose a special re hazard in laboratories Normal C02 re extinguishers cannot be used because burning magnesium reacts with C02 2MgC02 e2MgOC A Class D re extinguisher is required These use either graphite or very nely powdered NaCl Graphite reacts w1th Mg to form a magnes1um carb1de Class A B g solids which coats the magnesium and prevents further reaction Class B B g liquids w1th 92 NaCl melts and the 11qu1d coats the magnes1um Class C Electdcal effectively smothering the re Class D B g metals Industrially Mg is used in strong lowweight alloys with aluminum for structural materials Some lawn mower housings use this alloy Calcium and Barium Both are grayish metals that react with 02 slowly at room temperature but more rapidly at elevated temperatures Ca gives only the oxide while Ba give some peroxide dioxide 2 The charge to volume ratio of Ca2 52 Cmm3 is comparable to that of L while that of Ba 23 Cmm3 is comparable to that of Na 24 Cmm3 2 Ca s 02 g a 2 CaO s Ba s 02 g a Ba02 s 129 Because Xray absorption cross sections increase with the square of atomic number both Ca and Ba are Xray absorbers Slunies of the fairly insoluble BaSO4 are used in GI tract imaging Oxides and Hydroxides All M react with 02 to form MO with Ba also giving Ba02 MgO is insoluble in water and has an extremely high melting point 28250C and is refened to as a refractory compound High thermal conductivity but extremely small electrical conductivity make it useful in heating elements Other oxides react with water to give the corresponding hydroxide MO H20 a CaOH2 CaO is prepared by the thermal decomposition of CaCO3 at T gt ll70 C CaCO3 Ca0 co2 CaO alm quicklime emits a bright white light when a ame is directed against it hence limelight similar to behavior of Th02 which is used in camping lantern mantles CaOH2 aka hydrated lime or slaked lime has been used to adjust pH of soil upwards but CaCO3 can accomplish the same job without raising it to much MOH2 become more soluble as we descend the group7 OH Compound SOlubility is a fairly small anion and this trend follows the size mismatch g 39 L39 1 rule ofthumb MgOH2 1X10 4 Solutions of CaOH2 and BaOH2 react with C02 to produce CaOH2 12 the corresponding carbonate SrOH2 l 0 CaOH2 aq C02 g a CaCO3 s H20 0 BaOH2 47 Calcium Carbonate Ca is the 53911 most abundant element on earth found chie y as the carbonate in chalk limestone and marble deposits Chalk was formed is the seas mainly during the Cretaceous Period about 135 million years ago from the calcium carbonate skeletons of marine organisms Limestone formed as a simple precipitate and marble formed when subterranean limestone melted under intense pressure and temperature and subsequently cooled l 2 10 Underwater caverns like Carlsbad Cavems and Mammoth Cave occur in limestone beds Over geologic time scales rainwater with dissolved C02 entered small cracls and solubilized the limestone leaving vast underground voids CaCO3 s H20 0 C02 g a Ca aq 2 HCO339 aq Only allmli metal ions have suf ciently low charge densities to stabilize the large polarizable hydrogen carbonate ion so upon evaporation of water from solutions containing Ca2 and HCO339 ion CaCO3 is formed CaH0032 aq a Ca003 s H20 0 002 g Other Calcium Compounds Various silicate and aluminate compounds of calcium are important components of cement Hydrated calcium sulfate is the chief component in re resistant gypsum wallboard CaSO4 2 H20 s a CaSO4 12 H20 s 32 H20 g AH 298 83 1d Calcium chloride is an important dehydrating agent as well as icemelting agent CaC12 s H Ca2 aq 2 Cl39 aq AH 298 i 81 kJ Calcium carbide is actually a misnomer It s actually CaC2 dicarbide 2 formed in the reaction of CaO with C at 2000 C Ca0 3C a CaC2 CO This material reacts with water to produce acetylene CaC2 2 H20 a CaOH2 C2H2 This is a relatively safe and convenient source of acetylene for lamps for miners and spelunkers Calcium carbide also reacts with molecular nitrogen a relatively simple way of breaking the N E N triple bond 02102 N2 CaCN2 C The cyanamide ion is isoelectronic and isostructural with C02 and is a starting material in the synthesis of several organic compounds as well as being a slow release nitrogen containing fertilizer CaCN2 3 H20 a CaCO3 2 NH3 CHM 218 RCampO Chapter 3 l a LCAO stands for Linear Qombination of Atomic Qrbitals a model that assumes that molecular orbitals in a molecule are formed by a linear combination of atomic orbitals of all of the atoms in the molecule b A O orbital is an orbital that is formed by the headtohead overlap of atomic or hybrid orbitals on two or more atoms 0 V VSEPR Xalence hell Electron Lair Iepulsion Theory is a relatively simple model that assumes that valence electrons shared or unshared around an atom will be as far apart from each other as possible Molecular geometry is determined by these orientation that these electrons adopt d Hybridization is a model that assumes atomic orbitals on a central atom mix to produce hybrid orbitals that have directionality resulting in maximum overlap with orbitals on neighboring atoms 2 a Network covalent solids are those elements or compounds in which covalent bonds hold together all of the atoms of the crystal These substances typically have very high hardnesses and melting points Diamond and crystalline SiO2 quartz are examples b Intrarnolecular forces are the relatively weak attractive forces between atoms or molecules that hold the atoms or molecules together in the liquid or solid phase Examples are London dispersion forces dipoledipole forces and hydrogen bonds 0 V Electronegativity is a measure of the ability of an atom in a molecule to attract shared electrons toward itself d Hydrogen bonding is the attraction between a hydrogen atom covalently bonded to a highly electronegative atom such as F O or N and another such highly electronegative atom in the same or another molecule 3 The bond order is given by 12 of e39 in bonding MOs of e39 in antibonding MOs Since the bonding MO is doubly occupied and the antibonding mMO is T singly occupied the bond order is 12 39 r 939 1s 2 l12 Sincethereisan 1 l quot T unpaired electron the ion is S 15 paramagnetic quot 4 Since there is equal population of bonding and antibonding MOs Bez O is not expected to be stable The 18 diiTerence in energy between the AOs 18 l 1S andthe antibonding MO is actually xx greater than the diiTerence in energy 8 between the bonding MO and the I 15 AOs Therefore two separated Be atoms are more stable than the Be Bez Be diatomic Bez 5 bond order 12 7 e 2 25 See diagram 0 252 0 252 TI 2p4 0 2p1 7 NO is isoelectronic with CO so its bond order will also be 3 1l2p 8 The bond order will be 2 1f2p 9 Using the MO diagram which accounts for sp mixing we deduce a bond order of 1 Using the MO diagram which does not account for sp mixing we still obtain a bond order of 1 See next page The rst MO diagram predicts that B2 is paramagnetic with two unpaired electrons while the other predicts that B2 is diamagnetic 10 C27 0 252 0 252 TI 2p4 0 2p1 bond order 12 7 i 2 25 C27 0 252 0 252 TI 2p3 bond order 12 5 i 2 15 a b El p39 l cES39lt eE d CI 13 Either of the two resonance structures suf ces for the electron dot diagram The average bond order is 15 2 20 6 quot 2 l H u 39 14 u 0 0 The formal charges are indicated above each atom On the basis of minimizing the number of atoms with nonzero formal charges and reducing the magnitude of the formal charges the first structure is likely to contribute most followed by the third structure 1 0 0 2 0 31 HH The resulting partial bond representation is 001 sieve El Although the resonance structure that has the double bond between B and F has a formal charge of 1 on F and i l on B there is evidence that suggests there is signi cant overlap of a lled F rbital with the vacant 2pZ orbital on B electronic geometry a tetrahedral b tetrahedral c trigonal bipyramidal d octahedral electronic geometry a tetrahedral b tetrahedral c octahedral d octahedral i z DlBII F F molecular geometry bent trigonal pyramidal linear square planar molecular geometry tetrahedral tetrahedral octahedral square pyramidal 2 39n Cl quotquotCI CIquotCI C Cl 39CI 19 Only C82 and XeF2 are linear NOCl and SnCl2 N O N N L N 4 25 BrFZ39 and CNZ39 should both be are each based on a trigonal planar electronic 0 a s Cs geometry With one lone pair each will be bent 39 quot and should have a bond angle of somewhat less quot F than the ideal 120 ClO 2 has one lone pair and an unpaired electron Ideally it would be based on a tetrahedral electronic geometry with a bond angle of a little less that 109 5 u CI39H o Sn CI CI linear BrFf will be bent with a bond angle of somewhat less than 109 5 Br E l I l yBr E l OF2 and PCIS should have bond angles a little smaller than the ideal angle predicted by VSEPR Theory because of the unshared electrons Only SFS39 will exhibit distortion due to a lone pair The equatorial F atoms will be bent upward toward the apical F atom due to the increased volume requirement of the lone pair OF2 and PCIS are based on a tetrahedral electronic geometry steric number 4 and are therefore sp3 XeF2 is based on a trigonal bipyrarnidal electronic geometry steric number 5 and its hybidization is sp3d ICl439 is based on an octahedral electronic geometry steric number 6 and its hybidization is sp3d2 NH4 and CC4 are based on a tetrahedral electronic geometry steric number 4 and are therefore sp3 SiF 5239 and SF are both based on an octahedral electronic geometry steric number 6 and their hybidizations are sp3d2 2p 2p l 2p 2p LL iLiL 23t l 25 i g g a b c d a corresponds to the isolated Be atom Promotion of an electron is shown in b Hybridization of the occupied s and p orbitals results in two hybrid orbitals and two unhybridized p orbitals in c The hybrid orbitals will be 1800 apart accounting for the linear geometry d represents the pairing of the Be electrons in the hybrid orbitals with an electron from each of the two Cl atoms a b c d a corresponds to the isolated C atom Promotion of an electron is shown in b Hybridization of the occupied s and p orbitals results in four hybrid orbitals in c The hybrid orbitals will be 109 50 apart accounting for the tetrahedral geometry d represents the pairing of the C electrons in the hybrid orbitals with an electron from each of the four H atoms 27 The Se atom in HZSe has a greater polarizability than the S atom in HZS resulting in stronger dispersion forces and therefore a higher boiling point in HZSe The dipoledipole interactions in both are fairly weak with the HZS being slightly stronger but the dispersion forces are more important Neither HZS or HZSe is capable of hydrogen bonding N 00 Dispersion forces in ICl and Br2 are comparable but ICl has a permanent dipole which Br2 does not Because of the greater dipoledipole interactions in ICl ICl has a higher melting point N O OF2 and PCIS are polar XeF2 and ICl439 are nonpolar LA 0 NH4 CCl4 and SiFGZ39 are nonpolar SFS39 is polar LA Although dispersion forces in PI13 are stronger than those in NH3 NH3 is capable of hydrogen bonding The hydrogen bonds are stronger than dispersion forces so NH3 has the higher boiling point L N Although PI13 is slightly more polar than AsH3 the dispersion forces in AsH3 are stronger than those in PH3 and the dispersion forces are the stronger forces here AsH3 has the higher boiling point 33 a Inl is linear In is sp n quot quot In I Br SI39IBF BrSbuhll39Br b SnBr2 is bent Sn is sp2 quot Br c SbBr3 is trigonal pyramidal Sb is sp3 Tl ll F d TeCl4 is seesaw Te is sp3d CII i e 3 FF7EEI39I F e IFS is square pyramidal I is sp3d2 CI 34 We can rationalize this observation in several ways 1 N E The bonds in AsF3 are more polar than those in AsClg On average the shared electrons are farther away from the As atom in tha former than the latter allowing the bond angles to be smaller Cl is larger than F forcing the bond angle open so that the Cl atoms can be farther apart than the F atoms have to be According to Bent s Rule substituents of higher electronegativity bond through orbitals with greater p character while those of lower electronegativity and lone pairs prefer orbitals of less p character Since there are 1095O angles between sp3 hybrid orbitals and 900 angles between the unhybridized p orbitals bonds involving the more electronegative F atoms should involve more p character and therefore smaller bond angles Chzyter 14 e The Grnllp 14 Elements Group 14 consuls ofanonrmetal C two semlrmetals s and Ge tw eakmetalsSnande c s d pomts charactmsnc ofnonmetals l network dang llquld range Lhamselvesb gtgt sl gt Ge a the elemems catenate form chalns of atoms on utLhe ability to ealedaze decreases down he goup c Sn gtgt Pb sellmsamuu state Tm andlead also exhbltthe 2 oxldauon gate mempar effect Carth Diade amond form ofarbonthere ls a 400mg beeause an enormou energy ls needed to breakthese strong e v entbonds oxldauon my M nt i l l l hti J I Figure 142 Struclure 01 dlamond In normal d1am0nd the mngement oflhe celxahedrals the same as that m the cut holes Therels also an Extremely rare fonnlonsdalate named a erthe crystallogapher V M PM on dz structure Flmhw VP requlred The See energy of drarnondls 2 9 k1 rnolquot hrgher than that ofgraphlte It ls gmphlte Graphim wth m l r atomsm sxrmEmba39ednngs The Barbour comment wth thls assurnpnon The dlsfznce between the earbon layers ls very large Figure 1A 1 dr Waals radlus of a earbon atom Henee lhe acnaenon between layers ls very weak In the eornrnon hexagonal form of gaphlte aleemanng layers are allgned to gye an abab vr quot meal and below the centers of lhe nngs Mm nHFl ll m onrlmmrn W Thus glldmg on molecular ball beanngs narnely the adsorbed gas rnoleeules 0r om m m mtxudmg atoms M10115 mung between the layers m afarly stmchmmemc moo Fullerenes Fullerenes constitute a famny of structures m whmh Figure 5 r or elhpsmdal stxucture To make such astructure the carbon atoms form ve and slxrmemba39ednngs Evmnumbered fuller es from an Cmnarekn Wn 5x5 e esLsLablequErEne o a1 gh a neat degree ofbondstxam on sthe most reactive of me fullermes and deeomposes m au 10 000 C ofearbon atoms peel ofthe surface andwrap Lhamselvesmto balls Common soot Some amochemms argue Lhatthese molecules exist Extensively m mtersLellar mace r uh h u mu m u dAmIay bnghtyellowrgrem cm xsgolden yeuow All mefuueeeues subumewheu heaeed a property promdmg further evxdence of me weakmtermolecular forces A A cub manganent The fullerenes have low densities about 1 5 g em and they are nonconductors of elecmnty 14 4 The ellemlsby nfthesennvel mnleELLles ls sbll a eld dflmalseleseasell Tlle llleeenes ae easlly ledlleed le man by leaeadn Wllll Grnup l ald Grnup z metals lllbldlllm ts Wlddln Lhelnfasnces ln dle c5n lamee m gve Rbgcm Tllls eempellndls a Supa39cnndudnr at leenpelaalles 28 K beeallse its sauemle ls aamally Rb HcmZ The ma elemns assnnaeed Wllll lle flllleledes ae See on mnve mmuglellnlle ErySLal Just metal rel Example lee Lhasa ll a As dle cavmes ln dle llleledes ae quite large it ls pesslble m a ametal lull Wllldln dle sauemle An Example efmls ls Lang wharethe syman ls llsed m Indicate that be 3 melal lull ls Wlddln me Mlerens Carbm39l Nanntllbes Carbnn Nannmbes wele alsl dlseeyeed ln 1991 by he Japanese S m sllmle llllma afllllelele at eaell end They eal be made by lleabng gaph e m abnut 1200 C ll al lnell under p atmted Enndmnns lmmensely mngrabnut 100 rms that dfal equlvalent Strand nf SL331 Thus that39s are pmjected uses as a supeeslmng maeellal valdmg lle eabell hexagnns ale allgned pleelsely dle lung axls dfulenalembe dle mammal ls al hexagnns gylllg a er alanganenl dle mazenal bellayes as a semleelldllelel Chemxslxy of Carbon mdmhdnple bonding Condmons necessary for catenanOn Bond silicon Carbon has the greatest tendency toward catenauon of all me elemean capan ty 2 Tendency to bond with nself Kmeue memess of ams bond energy bond energy bond ad I molil bond ad I molil C C 345 Si Si 222 C o 358 Si 0 452 146 C also has a much greater propensity for multiple bond formation than Si The C30 bond energy is somewhat more than double that of Ce 0 but the longer SiO bond prevents effective p n p n overlap It has also been argued that the SiO bond has signi cant character due to p n d n backbonding I 43 H3 H3 6 Si O Si O Si O H36 CH3 clH3 CH3 n clH3 b d b 1 bond on energy bond on energy kJ mol 1 kJ mol l C0 358 SiO 452 CO 745 SiO Carbides Binary compounds of carbon with less electronegative elements other than H are called carbides These are typically hard highmelting solids which can be classi ed as either ionic covalent or metallic Ionic Carbides These are formed by the most electropositive elements Groups I and II and Al Most of these actually contain the dicarbide 27 ion C221 and react with water to form acetylene 02102 S 2 H20 0 v Ca0H2 211 Csz g BezC and A14C3 appear to contain C4 With such polarizing cations however there is likely considerable covalence although they do react with water to form methane BezC s 4 H20 0 a 2 BeOH2 s CH4 g Covalent Carbldes sllleon carblde slc and boron carblde Bc are Examples ofcovalent carbldes Both are very hard nlgrrnelang sollds slc ls preparedby the reaeaon of slo2 wth gaphlte at 2300 c ln a very energy lntenslve reaeaon 8025 3cs i SiCs 20mg Metallle earbloles erystal lataee of ametal and are usually formed by transmon metals The metal must the stolchlometxy ls l 1 These rnatenals are enrernely hard and mgr melnng They candid elecmclty well and are chemlcally reslstant Tungsten carblde wc ls used Exeenslvely ln eutnng tools When the metal atoms are not large oetalneolral holes the lamee 15 dlswned nhancedhardness to earbon steel mun quotelemquot ere new newton m Menquotan W Wm swam en qu r We r em am We tremor M NH tr 1m unlth Carbon Monon de Colorless odorless gas b p r 190 C Formedwnen earbon or earbon contamlng eornpounols are burned wth a de ciency of q co bond ls extremely short eonslstent wth a CObond 14 8 Preparation of CO CO can be prepared in a number of ways Reduction of C02 C02 H2 C0 H20 Steam reforming of methane CH4 HZO CO 3H2 Decomposition of formic acid HOOZH sto4 HzO 1 C0g Reactions of CO CO undergoes a number of important reactions Reduction of metal oxides Fe203s313g A 2Fel 3OQg Formation of methanol OO 2PL A 0amp0ng OX0 process coltggt 02H4ltggt mg A CszCHO Formation of transition metal carbonyls A N S 4 C0g gt Ni004 g 149 A more detailed discussion of transition metal carbonyls is available in sections 227229 In these compounds the metal has an oxidation state of O A wide variety of mono and polynuclear carbonyls are known with various binding modes for CO terminal bridging and capping O C CO oc M639 oo la 4 a 339 f Rd f quotquot quotH R m I v A 393 Eu I39J E C1 c D i39l M 39 Mm Ta Hg HI 0 o c c 0 llquotc MC CMc o S MRU 05 a O C c oo g oo O O b The structures of some trinuclear carbonyls Carbon Dioxide uquot3900 00 Ni39 CO u I g C a n 3 ca 1th he I P AlEL Cquot ml Er acacia L I 0 0c C o l C lr OC COO r lr C oC llr Co c C o L 0 0 a II The structures of tetranuclear carbonyls Carbon dioxide is a colorless odorless dense and relatively inert gas which does not burn and does not support combustion It will however react with buming metals 2Mgco2 azMgoC C02 is formed when carbon or carbon containing compounds are burned in excess 02 C02 does not exist as a liquid at normal atmospheric pressure A pressure of 6700 kPa is required to liquify C02 at 25 C Supercritical C02 is used to carry out a number of industrially important extractions mm I FEESILIH fIkPQL Illllh 333 25 39l39cni licmlilre VET TC 3 Phase diagram 14 10 Bonding m cq Carbonroxygm bond length and energy are comment wnh two c doublebonds Smplestxs theory hybndazanon theory and 0 CO molecular but theory all suppm Lhs observation 39 u m Mammy mhm r m mm 2 x o AcxdrBase B ehavxor of cq am i 4mm 1W co2 gHZO a Hzco3 aq K1 5 x 1039 H2C03aq HZOI Hco aq 1go39aq K 743x 10397 HCO aqHzOl C03quot aq HO39aq K247x1039 A W Pr react the ma K10fH2C03xs about 2 9 x10quot At pH 5 8 the neutnhzanon of cq occurs by hydration of cq co2 g HZO a HZCOK aq HZCOZ aq OH39 aq Hco aq HZO a 14 11 At pH gt10 the neutxahzanon of cq oeeurs by duect reaeuon ofco1 wuh OH co2 aq OH39 aq Hco aq Hco aq OH39 aq co aq 1120 1 co2 and the Greenhouse Effect e eath s greenhouse effect or rad1anonh39app1ngquot 15 whatmakes Earth suxtzble forhfe as we know r1 Solarra auon 15 absorbedby the Earrh39s surface and atmomhane and rermdAated m the form ofmfrared radrauon The earrhs atmospha39e eonrarns uaee gases HZO co cm 0 and N20 whreh absorb the gemhouse gases The Golddocks Pnnup1e Venus 15 too hot Mars 15 too eolaL and Earrh stusL ngnr kmd of atmosphere Venus39 atmosphere 96 lt 1 co Ar so2 and H20 at apressure of9 kPa and 45010 and Mars39 atmosphere 95 d 50 C wou1o1be cq 3 5 N2 mtxogen 000 13 0 x H H u n co2 a apressureof1 aan not be smtableforhfe as we know r1 a rush nn m n susnn mum Polyawmm rno1eeu1es orherrhan hornonue1ear dAatomxcs absorb mfraredradwnon andtherefore oeo 6 5 conmbuteto the gemhouse 3331 Lem W m 1 Wm sun Water 15 the predommant greenhouse gas but us unnr nuuusornucs rune aunosphene oncentxanon andLhereforextseffecton Wu Museum an ornenon known as g1oba1 Warmmg m Concmiml u mm l 4 12 Carbonates and Hydrogen Carbonates Only the alkali metals other than Li form stable solid hydrogen carbonates which decompose on heating MH003 s A M2003 s Hzo I cog g The carbonate ion is quite basic due to its hydrolysis CO32 aq H20 0 HCO3 aq OH aq Bonding in CO3239 CO bond lengths are identical but shorter than a C4 single bond The O bonding makes use of a set of sp2 hybridized orbitals on C leaving an unhybridized p orbital from C and a single p orbital on each 0 for nbonding Carbon Disul de Carbon disul de is the sulfur analog of carbon dioxide with a linear geometry It is a colorless to pale yellow nonpolar volatile and toxic liquid bp 46 C It is prepared by passing methane over molten sulfur at 700 C and cooling the products to condense CSZ A CH4 g t 4 S 1 032 g t 2 H25 g It is used as a solvent for nonpolar solutes like P4 as well as a starting material for other compounds l 4 13 Hydrogen Cyanide and Cyanides HCN is an extremely toxic gasliquid bp 26 C CN is a pseudohalide so HCN is a covalent molecular substance HCN is an extremely weak acid pKa 921 and cyanides are hydrolyzed to HCN in aqueous solution It is prepared either by the Degussa Process Pt 1200 C CH4g NH3 9 HCNg 3 H2 g or by the Andrussow Process PtRh 111 C 2CH4g2NH3g 302 2HCNg6H20 g Toxicity of CO and CN Even though CO and CN are isoelectronic their mechanisms of toxicity are di erent CO binds more strongly to hemoglobin than does 02 reducing the availability of hemoglobin for 02 transport Hbo2 CO HbCO 02 K 210 CN interferes with e transport by cytochrome oxidase c which is necessary for respiration and depends on the FenFe 1 redox couple CN coordinates to the Fe center in the cytochrome and stabilizes the FeIII interfering with electron transfer The most effective treatment for CO poisoning is oxygen therapy In accord with LeChatelier s Principle excess 02 will displace CO from hemoglobin Treatment for cyanide poisoning involves either conversion of CN to the less toxic SCN ion with thiosulfate CN39 203 w SCN39 303239 or oxidizing Hb to metHb which binds CN more tightly than Hb or cytochrome c and can effectively remove it from the body HbFeH amp HbFeII 14 14 sllleon by rn s It foundln yanous srlreate rnrnerals eontarnrng 5H bonds Ultrapure sllreon for sernreonoluetor applreataons ls prepareol by a mLLlnestep proeess 510215 redueeolto 5r uslng eoke A mum SOzs2Cs Sil 2co t t t punfled to the ppb level by ernausnye dlsnllanon Sls3HClg EC SlHC13g H2g W V m u h u t not suf clendy pure 5r SiHClKQg H204 A Sis 3HClg lElElEI C Further pun canon ls earned out by zone relinlng wlnen mamquot V quot 539 relres on the factthat lmpunnes wlll be excludedfrom Lh lamee when llquld 5r erystalbzes Uluapulc sl Srlreon Dloxlde slllca st Dewrte slrnrlar formulas cq and so2 are strueturally drsnnet Whlle cq l3 ls a gas at room temperature due to weak disparlen forces 5ro2 ls h 1 melung1600 c eoyalent network solldfor reasons preyrously dlscussed t Slllcals falrly unreaetaye noweyer rt does reaet readily wlth HF and F2 le2 s 6 HF aq e Sng39 aq 2H aq 2Hzo l 14 15 As well as wrth strong bases 02 OH and fused earborrates so2 2Na0H NaZSlOK H20 F rlhl r ason es bottl Glasses and slbeates 9 e are rrorrerystallme materrals When erystallme srlreorr dloxldels heatedto aboye 2000 c and allowedto eool rts yrseosrty gradually mereases urrul solldlfles wrthout crystalllzmg r ung n wha ll quartz mp expausrorrresulurrg m exeellert erm s oek reslstaree and ummarerrey m the UV the mgr worldrrg temperature of quartz makes rt to expenslve for rouurre applreauorrs The yrseosrty of the quuld and rts worldrrg temperature can be redueed by breaklng some othe Sr or St bndgng borrds foundln so2 Addmon of Nap usually as NaZCOX to molterr slhca reduees the yrseosrty and thermore the workmg temperature by brealdrrg some ofthe bndglng bonds Soda glass has a low worldrrg temperature but poor water Addmg Caoredueesthe solublllty Most of theglassusedtoday wlndowsbotd35 ete ls sodae e slhca glass hm n trm arm msiau The addluon ofB103 to sodaglassreduees the quot solublllty as well as the thermal expanle eoel umt Borosrlreate Pyrex m glasses are used when thermal s oekresrstauee ls needed 14 16 Slllcates u u r possble Kali me bndgng bonds are brokenuneresrllrsuneleuaneolral onhoslllcate ron soquot so2 2 NaZCOX NaSro 2 co2 When halfthe bndgng bonds are broken so2 0139 a so andLheresultls almearcham slhcate structure 0 0 u l l u u Su u 1 Si 0 0 O l0 1 0 O l 0 Sr 0 l 5n n s l r l l o 0 l 0 l 0 Moon l urn l m Chum Svozzriyywkemw39 A double Eham or rn nme band oeeurs m a elass of mmemls ealled amphlboles Asbestos and relafzedmmerals have ths stxucture whlnh results m their brous nature a of the budglng bonds are broken zlSro2 3 0139 soon 0 0 r l S 0 l o o u l loll n s l s r l o 0 l 0 l u s o 51 run 0 n o lo s39 0 5r 0 r U r r o 0 o r l mm r ml on Hand suo quot39lnnpuruolesx 14 17 Lu uue sheets resultmlayeredmmerals sueh as mxca talc andvanous clays Thxs structure results from me breakmg of VA othe bndgng bonds 2502 0139 a 5205 1 4 1 8 Silanes Monosilane is prepared by heating SiO 2 with LiA1H4 at 150 to 170 C Higher silanes are prepared by photolyzing mixtures of SiH4 and H2 in a reaction where SiH2 might be an intermediate Of the silanes only monosilane SiH4 and disilane SizH6 are inde nitely stable at 25 C Higher silanes are spontaneously ammable in air Si4H10 132 02 4 SiO2 5 H20 Silanes are stable to water and dilute mineral acids but subject to rapid base hydrolysis SizH6 4 n H20 4 2 Si02 n H20 7 H2 Germanium Germanium and silicon both have a diamond structure The graphite structure is unique to carbon Like Si germanium is used in semiconductor deVices Germanium is prepared by the reduction of its oxide with either carbon or hydrogen GeO2 2C 4 Ge 2C0 Ge02 2H2 HGe 2H20 1419 Tin and Lead Tin has two common allotropes Gray at tin dull gray in color brittle diamond structure semiconductor p 575 g 39 cm 3 at 20 C stable below 13 C White 13 tin silva in color with charact istic metallic lusts malleable tetragonal lattice mdallic conductor p 731 g 39 cm 3 at 20 C stable above 13 C 13 C ZI ZOC octln gt tln gt llquld Lead exists only in the ccp mdallic form re ecting vay low stability of the Pbin bond It is a very dense very soft dark gray metal 1 A 1 Huh 4 r 1 PM Itisemmdby mm to PbO and SOZ and reducing the PbO with coke PoSs302gA 2PoOZSOZg ms Cs 1171 0mg anironmentalconcem39 39 SOZ L 4 quot 39 andreleaseof toxic leaddust 14 20 Oxides of Tin and Lead Tin IV oxide SnOz is the more stable oxide of tin while of lead II oxide PbO is the more stable oxide of lead PbO occurs in two forms litharge red in color with a layered structure and massicott yellow in color with a chain structure Pb02 is chocolate brown in color It is chemically stable and a good oxidizing agent In addition red lead Pb304 lead II lead IV oxide can be prepared by heating either PbO or Pb02 in air It behaves chemically as if it were a mixture of PbO and PbOz but the structure involves PbIVO6 octahedra linked in chains by the sharing of opposite edges The chains are linked by Pb1 ions each bound to three 0 atoms Chlorides of Tin and Lead Tin IV chloride is atypical covalent metal chloride It is an oily liquid which reacts with ambient moisture to give a hydrated oxide of tin which is represented as SnOH4 SnC14 0 4 H20 0 a SnOH4 s 4 HCl g Lead IV chloride is also an oily liquid yellow in color which decomposes when exposed to ambient moisture explosively when heated PbBr4 and PbI4 do not exist because Br and I are not suf ciently reducing to stabilize PbIV Lead II chloride is an insoluble white solid with an ionic crystal lattice but tinII chloride exhibits covalent character as evidenced by bridging chlorides and solubility in low polarity solvents In the gas phase SnCl2 is bent with a bond angle of about 95 suggesting that the orbitals used for bonding are essentially pure p orbitals SnClZ does not exhibit Lewis base behavior but instead acts as a Lewis acid 11012 or SnClg39 The lone pair appears to occupy a spherical s orbital
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