CHEM 107 Lecture Notes - Lecture 52: Formal Charge, Lewis Structure, Electronegativity

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11 Aug 2017
School
Department
Course
4-18-17-Resonance Structures
Tuesday, April 18, 2017
10:56 AM
Week 12-Chemical Bonding
-Lewis Structures
-Molecular Geometry
Electronegativity
-Describes the ability of an atom to attract electrons
Formal Charges
Formal charge = (valence e-) - (non-bonding e-) - (# of bonds)
-The sum of the formal charges should always equal the overall charge of the
compound (0 for neutral)
-The best Lewis structure will have the lowest formal charges on all atoms
-If multiple structures have lowest formal charges, the most electronegative
atom should have the most negative formal charge
Resonance Structures
Resonance Structures
-describing molecular structures with 'delocalized' electrons
-does not change the overall formal charges
-hybrid between a single and double bond
-generally if you don't see a double bond, it doesn't have a resonance structure
SO3 in the picture (on phone) has 2 delocalized e-
S-O Bonds in this molecule have
-equal bond strengths
-equal bond lengths
Electrons are NOT moving/jumping/shifting between atoms
Exceptions to the Octet Rule
1. Odd number of valence electrons in molecule
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Document Summary

Describes the ability of an atom to attract electrons. Formal charge = (valence e-) - (non-bonding e-) - (# of bonds) The sum of the formal charges should always equal the overall charge of the compound (0 for neutral) The best lewis structure will have the lowest formal charges on all atoms. If multiple structures have lowest formal charges, the most electronegative atom should have the most negative formal charge. Generally if you don"t see a double bond, it doesn"t have a resonance structure. So3 in the picture (on phone) has 2 delocalized e- Exceptions to the octet rule: odd number of valence electrons in molecule, less than on octet (h, be, b, al common) Boron and aluminum will only ever have 3 bonds: more than an octet (n=3 and above since d orbitals available) H3po4 has two resonance forms and formal charges indicate the more important form.

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