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TRANSCRIPT
UMass Amherst Biochemistry Teaching Initiative
Chem 241Lecture 3
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Homework Chapter 1
o Should have already read chapter 1.o Start reading chapter 2.
Exercise: 2, 3, 5, 11, 12, 13, 15, 17, 20Problems: 10, 11, 12
One of the questions doesn’t give you enough info:strontium, barium and radium have first ionization energies of 5.69, 5.21, 5.28 eV.
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Recap
Showed how the wavefuntion relates to orbital characteristics.
How to fill the orbitalsHow Zeff effected the orbitalsHelp to understand why the periodic table is arranged the
way it is and how this give rise to periodic trends.
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Ionic Radius
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Ionization energyEase in which an electron can be removedA(g) A+(g) + e-(g)I = E(A+) – E(A)First Ionization Energy, I1Second Ionization, I2Energy is determined by the HOAO
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Ionization Energy
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Electron affinity
Ease in which an electron can be addedA(g) + e- (g) A- (g)Ea = E(A) – E(A- )Energy is determined by the LUAO
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ElectronegativityThe power of an atom to attract electrons when it is part of a compoundPauling - χp : based on bond formationMulliken - χm = 1/2 (I + Ea)Allred-Rochow -
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EN
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PolarizabiltyAbility to have its electron field distorted by another field
Fajan’s RulesSmall, highly charged cations have polarizing ability.Large, highly charged anions are easily polarized.Cations that do not have noble-gas config. Are easily polarized.
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Chapter 2. Molecular Structure and Bonding
Inorganic chemists are adept at describing the molecular shapes of molecules and describing the bonding and electronic structures starting with qualitative “guesses” and building complexity from there. • Review of Lewis Structures• Review of Valence Bond Theory• Review of molecular orbital theory• MOT descriptions of inorganic molecules.
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Lewis StructuresI. Emphasize covalent bonding• A. Rules
• 1. a bond corresponds to a shared pair of electrons• A:B or A-B• A::B or A=B… quadruple bonds in some metal
complexes.
• 2. Unshared pairs of electrons are called lone pairs and do not contribute to bonding, but are stereochemically active.
• 3. Octet Rule (Noble gas configuration)
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Lewis Structures• 5. determine the number of valence electrons taking
into account overall charge.
• 6. Arrange chemical symbols of elements to show which are bonded together (usually the least electronegative element is in the middle).
• 7. Distribute electron pairs sot that each bond has a pair of electrons. Then distribute remainder to lone pairs and multiple bonds to satisfy the octet rule.
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Lewis Structures
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Lewis StructuresResonance Structures
• 1. used to describe equivalent structures• 2. average bond characteristics • 3. energy of resonance hybrid is lower
Minimize formal charges• f = V – L - 1/2P
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Oxidation States
CrO42-
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Lewis StructuresHypervalence and octet expansion occur for elements following period 2.
hypervalent Octet expansion
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Bond Length• Equilibrium Bond Length is the distance between the center of two bonded atoms.• Contribution of each atom is the covalent radius.• van der Waals radius are the “closeness” nonbonding atoms get to each other.
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Bond Strength• AB(g) A(g) + B(g) .
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ElectronegativityE = (A-B)bond - ½ {(A-A)bond + (B-B)bond}If difference was greater 1.7 then it was ionic.
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VSEPR (valence shell electron pair repulsion)
Basic Tenents• 1. Regions of high electron
density (bp(s) + lp(s)) take up positions as far apart as possible.
• 2. Molecular shape is determined by the resulting atomic positions
• 3. lone pairs take up more space than bond pairs
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VSEPR
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VSEPRConsider SO3
2-
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Valence Bond TheorySpin pairing of electrons in overlapping atomic orbitals. Consider H2, 1s1
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Valence Bond TheorySpin pairing of electrons in overlapping atomic orbitals. Consider N2, 2s2spx
12py12pz
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