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I. Lewis Diagrams

– Molecular Structure. I. Lewis Diagrams. A. Octet Rule. Remember… Most atoms form bonds in order to have 8 valence electrons. F F F S F F F. F B F F. H O H. N O. Very unstable!!. A. Octet Rule. Exceptions :. Hydrogen  2 valence e -.

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I. Lewis Diagrams

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  1. – Molecular Structure I. Lewis Diagrams

  2. A. Octet Rule • Remember… • Most atoms form bonds in order to have 8 valence electrons.

  3. F F F S F F F F B F F H O H N O Very unstable!! A. Octet Rule • Exceptions: • Hydrogen  2 valence e- • Groups 1,2,3 get 2,4,6 valence e- • Expanded octet  more than 8 valence e- (e.g. S, P, Xe) • Radicals  odd # of valence e-

  4. 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 aren’t enough e- to go around, form double or triple bonds.

  5. B. Drawing Lewis Diagrams • CF4 1 C × 4e- = 4e- 4 F × 7e- = 28e- 32e- F F C F F - 8e- 24e-

  6. B. Drawing Lewis Diagrams • BeCl2 1 Be × 2e- = 2e- 2 Cl × 7e- = 14e- 16e- ClBeCl - 4e- 12e-

  7. B. Drawing Lewis Diagrams • CO2 1 C × 4e- = 4e- 2 O × 6e- = 12e- 16e- OCO - 4e- 12e-

  8. 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.

  9. C. Polyatomic Ions • ClO4- 1 Cl × 7e- = 7e- 4 O × 6e- = 24e- 31e- O O Cl O O + 1e- 32e- - 8e- 24e-

  10. C. Polyatomic Ions • NH4+ 1 N × 5e- = 5e- 4 H × 1e- = 4e- 9e- H H N H H - 1e- 8e- - 8e- 0e-

  11. D. Resonance Structures • Molecules that can’t 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.

  12. O O S O O O S O O O S O D. Resonance Structures • SO3

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