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CHEMl 11 General Chemistry 1 Electron Pair Geometr Total Electron Pairs 2 6 DL Adams Apnl 18 mm Lone Pairs 0 linear trigonal planar trigonal planar tetrahedral tetrahedral tetrahedral trigonal bipyramidal trigonal bipyramidal trigonal bipyramidal trigonal bipyramidal octahedral octahedral octahedral 90 amp 120 87 amp 116 90 88 amp 90 90 Molecular Shape linear trigonal planar bent V shaped tetrahedral trigonal pyramidal bent V shaped trigonal bipyramidal Seesaw T shaped linear octahedral square pyramidal square planar EPG and Molecular Sha e Examples BeClz BF3 N02 CH4 BH4 NH3 H20 ClF3 Xer Cle CHEM111 General Chemistry OXIDATION NUMBER ON The oxidation number of a monatomic ion is the charge on that ion The oxidation number of an atom in a molecule or polyatomic ion is a fictitious number equal to the charge that atom acquires when all its bonded electrons are assigned completely to the more electronegative element Rules for the assignment of ONs 1 Uncombined atoms ie Fe or atoms in a molecule ie 02 of an element have an ON 0 ie the oxygen atoms in both O or Oz have ON 0 2 Monatomic ions ie NaH have an ON the charge on the ion ie Na has an ON 1 and 8239 has an ON 2 3 F always has an ON 1 ie in HF OF2 and NaF among others 4 0 almost always has an ON 2 EXCEPT in a peroxides containing the 02392 ion where ON 1 b superoxides containing the 02139 ion Where ON 12 and c in OF2 where ON 2 5 H almost always has an ON 1 EXCEPT in metallic hydrides ie NaH where its ON 1 6 The sum of the ONs in a polyatomic ion must equal the charge on the polyatomic ion ie in SO42quot the ON of S 6 7 The sum of the ONs is a neutral compound must equal zero PS the nonmetallic elements have a range of oxidation numbers they can have The highest is equal to the number of the A group it occupies and the lowest is the charge on its monatomic ion e g chlorine has oxidation numbers ranging from 7 to 1 and nitrogen has ONs ranging from 5 to 3 BL Adams 2182007 CHEMl 11 General Chemistry 1 RESONANCE AND RESONANCE STRUCTURESII A single Lewis electron dot formula often adequately represents the locations of bonding electrons T T T in molecules For instance methane and ethyl alcohol are HCH HCC correctly represented by the Lewis formula at the right I quot All electron pairs in these molecules are localized H H H 39 between the atoms that share them methane ethyl alcohol There are however molecules whose electronic distribution is inadequately represented by a single Lewis formula In these cases two or more Lewis formulas may be necessary to satisfactorily represent the molecule Resonance is a phenomenon invoked when more than one Lewis formula is needed to adequately describe the electronic distribution in a molecule Resonance is the use of contributing structures to represent electron delocalization dispersal in a molecule For example consider the sulfur dioxide S02 molecule Structural studies show that both SO bonds in S02 are of the same length and the same strength This electronic distribution is not explained by either single Lewis structure but is explained when both Lewis formulas are taken into consideration OS I OS 039 Q 9 e u quot 39 Both Lewis structures are called resonance structures or resonance contributors Resonance contributors are separated by double headed arrows as shown The actual molecule is NOT an equilibrium mixture of the imaginary resonance structures but rather a single unchanging composite structure called the s resonance hybrid Resonance hybrids are often represented by the quotpartial bondquot or combined notation The resonance hybrid for sulfur dioxide is shown 0 e p to the right Fundamentally the phenomenon of resonance is invoked because of the inability of single Lewis structures to show electron delocalization within the molecule In fact resonance is often called delocalization For instance in S02 two electron pairs are delocalized or spread over the entire OSO three atom bonding system and not localized in a single SO bond Thus the existence of electron delocalization in a molecule means that more than a single resonance structure must be drawn to fully describe the electronic distribution within the molecule Furthermore since electronic delocalization is stabilizing the existance of resonance implies molecular stabilization Generally the more resonance contributors the more stable the molecule Resonance amp Page 2 18 April 2007 Resonance Structures DRAWING RESONANCE STRUCTURES Resonance structures differ only in the location 0ftheir electrons The atomic nuclei must not move and the bond angles must not change Resonance structures must all contain equal numbers of electron pairs and or unpaired electrons One resonance structue can be converted to another by electronic movement denoted by curved arrows For instance the two resonance structures for S02 are interconverted by the electron movements shown 9 9 sf lt 38 Of course no actual electronic movements O 39O 6 e 39 0 occur this process is an aid in generating additional resonance structures Another example of this relationship among resonance structures is shown with the three resonance structures of the nitrate ion NO3391 C 9 0 lt2 7 Z o The implications of resonance are 1 the actual electron distribution is different than would be expected based on a single Lewis structure and 2 the energy of the actual molecule is lower than expected from a single Lewis structure This energy lowering is due to electron delocalization and is called resonance stabilization The degree of energy lowering or molecular stabilization is related to the number of resonance structures and the relative stabilities of the resonance structures arns April 13 2007 CHEM111 General Chemistry 1 QUANTUM NUMBERS The Schrodinger wave equation describes the energies of an electron in an atom Solutions to this equation are called wave functions and in addition to describing the energy of an electron they also describe the shape and orientation of the volume element in which the electron exists The solutions are restricted due to three quantum numbers Acceptable solutions are called orbitals An orbital is a region in space or a volume element where there is a high approximately 90 probability of locating an electron Each orbital is uniquely de ned by a set of three quantum numbers The quantum numbers describe restrictions that are needed to nd solutions to the Schrodinger equation they therefore limit the number of acceptable solutions The three quantum numbers are described below 1 Principal guantum number 1n n has whole number values from 1 to in nity 11 indicates the approximate distance of the orbital from the nucleus and therefore its approximate energy For example an electron in an orbital with n 3 is located at a further distance from the nucleus than an electron in an orbital with n 2 and therefore has a higher potential energy The principal quantum number is essentially the principal level postulated in the Bohr theory 2 Angular momentum guantum number m may have values from 0 to nl Therefore the number of values is equal to 11 de nes the three dimensional shape of the orbital For example when 0 the orbital is spherical and when I l the orbital is shaped like a dumbbell values are generally given letter designation as follows 0 s l p 2 d 3 f 3 Magnetic guantum number 1mg mmay have values ranging from 0 m describes the orientation of the orbital in space For example when l m 10l These three mvalues describe three p type orbitals all of which have different orientations in space along the three coordinate axes An orbital is designated by its principal quantum number followed by its angular momentum quantum number or nl For example the orbital with n l and l 0 is called a ls orbital and when n 3 and l 2 this is a 3d orbital Orbitals with the same values for n andl but different values of m are differentiated by using subscripts x y and z for the coordinate axes along which they are oriented For example the three 2p orbitals are oriented along the x y and z coordinate axes and are therefore called 2px Zpy and 2pz Each orbital is uniquely described by a set of three quantum numbers The ls orbital is de ned by the three quantum numbers of 100 where the rst is n the second 1 and the third ml The three 2p orbital are described by 2ll 210 and 21l Quantum Numbers Summary Principal Angular Magnetic Quantum Quantum Quantum Orbital Number n Number I Number m Orbitals Type Electrons l 0 0 l ls 2 2 0 0 1 2s 2 1 101 3 2p 6 3 0 0 1 3s 2 1 101 3 3p 6 2 2 l0l2 5 3d 10 4 0 0 1 4s 2 1 101 3 4p 6 2 2l0l2 5 4d 10 3 32l0l 23 7 4f 14 n 0 n1 0 n2 2n2 total n A level is a collection of orbitals with the same value of n Thus the third principal level has 9 orbitals and 18 electrons A sublevel is a collection of orbitals with the same values of n and 1 Thus the 2p sublevel is a collection of the three 2p orbitals 2px 2py and 2pz The third level is composed of three sublevels the 3s 3p and 3d The number of sublevels for any given level is equal to the level number 11 All s sublevels contain 1 orbital and a maximum of 2 electrons p sublevels contain three orbitals and a maximum of 6 electrons and d sublevels contain 5 orbitals and a maximum of 10 electrons 0616b 17 2008 CHEMl 11 General Chemistry 1 Thermochemit Notes cha ter5 Chemical reactions accompanied by heat changes evolution or absorption Evolution 7 re fuel combustion food metabolism Absorption 7 cold packs ice melting The study of heat changes in chemical reaction is called thermochemistry Thermal energy is another name for heat and is de ned as a form of energy contained by matter as a result of the motion of its component molecules or other particles ie a form of kinetic energy Do not confuse temperature with thermal energy or heat Temperature measures the average kinetic energy of molecules while thermal energy measures the absolute quantity of energy present For example a bathtub and thimble might contain water at the same temperature average kinetic energy of molecules but there is a lot more heat in the bathtub than the thimble Energy 7 ability to do work or transfer heat Amorphous ephermeral Energy is observed only during its transfer from one form to another D0 work 9 displacement in the surroundings W F X d Transfer Heat 9 cause a change in the temperature AT Empirical observations show that when systems chemical reactions do work or transfer heat these changes always obey the law AEq W where AE is the change in the internal energy of a system and is composed of kinetic and potential energy components Thus when the internal energy of a system decreases the released energy may either be used to do work or transfer heat to the surroundings So the change lowering in this case in internal energy causes either a displacement or a temperature change in the surroundings This is the First Law of Thermodynamics or the Law of Conservation ofEnergy The sign conventions regarding energy ow to and form a system are crucial When the internal energy of the system decreases the arithmetic sign of the energy change is negative meaning that the system has lost internal energy and its internal energy decreases Thus work done on the quot and heat f 39 to the quot are both negative On the other hand work done on the system and heat transferred to the system are both positive The positive values indicate the system has absorbed this energy and as a result its internal energy has increased ie positive DL Adams September 30 2008 CHEM111 General Chemistry 1 SUMMARY OF ORBITAL HYBRIDIZATION RULES Hybridization is a phenomenon where atomic orbitals AOs on the same atom quotmixquot to yield mixed or hybrid orbitals During the hybridization process the following are true 1 The number of hybrid orbitals produced equals the number of atomic orbitals mixed For example one quotsquot orbital and two quotpquot orbitals yield three hybrid orbitals after hybridization 2 Hybrid orbitals are given symbols and are named according to the number and type of atomic orbitals involved in hybridization For example when one quotsquot orbitalzand two quotpquot orbitals undergo hybridization the resulting three hybrid orbitals are each called quotsp quot hybrid orbitals the superscripts indicate the number of that type of orbital used in the hybridization Thus sp2 hybrids always come in sets of three 3 Hybrid orbitals of the same type such as sp3 have the same shape 4 Hybrid orbitals are strongly directional They are oriented in speci c spatial directions around the atomic nucleus to be as far apart as possible similar to VSEPR For example the four sp3 hybrid orbitals form a tetrahedral shape In general the type of hybridization used by a speci c atom in a molecule or ion can be predicted by determining the number of attachments to that atom An attachment is de ned as a bonded atom regardless ofthe number of bonds to it or a non bonding pair of electrons Note there are exceptions to this rule for many situations however this simple rule applies Attachments H lgbridigation Geometr Anglqsz 6 spsd2 octahedral 9001800 5 spsd trigonal bipyramidal 9001200 180 4 sp3 tetrahedral 109 50 3 sp2 trigonal planar 1200 2 sp linear 1800 DL Adams 4 May 2007 CHEMl 1 1 General Chemistry The lemon yellow element sulfur has been known since ancient times This non metal was often called brimstone by the ancients It has an atomic number 16 and atomic weight 32066 u It is essential to life due to its presence in amino acids such as methionine and cysteine The average person ingests between 850930 mg daily in the form of protein The average 70 kg person contains about 140 g of S Sulfur has been used as a medicine since ancient times for digestive disorders and more recently to treat the bacterial source of rosacea Sulfa drugs the earliest antibiotics contain sulfur in the molecules of the drugs There are 11 isotopes of sulfur four of which occur naturally The naturally occurring isotopes and their percent abundances are S32 9502 S34 421 S33 075 and S36 002 The atomic weight of S 32066 u re ects this distribution Sulfur is found in nature as elemental molecules containing eight sulfur atoms or S8 Sulfur has a density of 2070 gmL and a melting point of 112 C The main natural source of sulfur are the metal pyrites such as iron pyrite FeSz Early chemists observed that when sulfur reacts with chlorine Z17 the formula of the product is SClz They also observed that the elements oxygen and selenium also react with chlorine to yield products with like formulas OClz and SeClz respectively Other elements react with oxygen to give products of different formulas CHEMl 11 Reaction Types Synthesis 7 combination of two or more substances to form a new substance Most often two elements combine to form a compound or a compound combines with an element to form a new compound Na C12 9 2 NaCl 2 H2O 02 9 2 H202 In general A B 9 AB Decomposition 7 most often a breakdown of a compound into its elements or the 39 39 39 of a J into a 39 and an element or two new compounds r r 2 H20 9 2 H2 02 CaC03 9 Ca0 CO2 In general AB 9 A B Single Replacement 7 a reaction in which one element of a compound is replaced by another Mg 2HCl 9 MgC12 H2 In general A BC 9 AC B Double Replacement 7 a reaction in which two compounds exchange parts Also called metathesis from Greek to place differently HCl KOH 9 KCl HOH or H2O AgNO3 LiBr 9 AgBr LiNO3 In general AB CD 9 AD CB H E LI t Fig F f f 1 L F I r E g I x F L ran F 2 It ER j Lii i w 39 7 4 2L V I OHEm Hf 3123106 geesHum MM775 77me 14 h 1 2771 32 H w W E quoti 7 H if GE 2963 W a TiN L 7 lefxloId Cgic LWW Cd 1 g 7773 I A Zpl AO a Eh 1 a wax0quotquot 3 mm mm 0 mm 950 10495quot x Lem5 m fifi mls imam WV mb czju 911ng of 77917 am If 51m 7 0 Cala i 77 777777 Sing 413 M Ma I 6 AC av X hi 5 7 ine W i LAZM5 VEZXJL Kii g i 39 4 7052 IoHV 7 0 0m a A 9 o k I m W w 71ng jaxz m V Calmamaog 291494 g 39KwaCya Ew wrrui ev th39h Libb 53ng 7 WI T A 9 39m 1pr 139 15294 9 EECW 039 7m 7