# Ch. 13 - Molecular Structure

Ch. 6 Molecular Structure I. Lewis Diagrams (p. 170 175) I II III A. Octet Rule

Remember Most atoms form bonds in order to have 8 valence electrons. A. Octet Rule F F Hydrogen 2 valence e F B F Groups F

S F 1,2,3 get 2,4,6 valence e H N O O H Expanded octet more than 8 F Very Fe (e.g.unstable!!

valence S, P, F Xe) Exceptions: - - Radicals odd # of valence e- -

B. Drawing Lewis Diagrams Find total # of valence e-. Arrange atoms - singular atom is usually in the middle. Form bonds between atoms (2 e-).

Distribute remaining e- to give each atom an octet (recall exceptions). If there arent enough e- to go around, form double or triple bonds. B. Drawing Lewis Diagrams CF4

1 C 4e- = 4e4 F 7e- = 28e32e- 8e24e F F C F F B. Drawing Lewis Diagrams BeCl2 1 Be 2e- = 2e2 Cl 7e- = 14e16e- 4e12e Cl Be Cl B. Drawing Lewis

Diagrams CO2 1 C 4e- = 4e2 O 6e- = 12e16e- 4e12e O C O C. Polyatomic Ions To find total # of valence e-: Add 1e- for each negative charge. Subtract 1e- for each positive

charge. Place brackets around the ion and label the charge. C. Polyatomic Ions ClO41 Cl 7e- = 7e4 O 6e- = 24e31e+ 1e32e- 8e24e O O Cl O O C. Polyatomic Ions NH4+ 1 N 5e- = 5e4 H 1e- = 4e9e- 1e8e- 8e0e

H H N H H D. Resonance Structures Molecules that cant be correctly represented by a single Lewis

diagram. Actual structure is an average of all the possibilities. Show possible structures separated by a double-headed arrow. D. Resonance Structures SO3 O O S O

O O S O O O S O

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