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Lewis Diagrams (p. 220 – 229)

Ch. 8 – Molecular Structure. Lewis Diagrams (p. 220 – 229). A. Drawing Lewis Diagrams. Arrange atoms Singular atom is usually in the center (often Carbon) If no Carbon, least e - neg atom is in center Hydrogen is always terminal

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Lewis Diagrams (p. 220 – 229)

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  1. Ch. 8 – Molecular Structure Lewis Diagrams(p. 220 – 229)

  2. A. Drawing Lewis Diagrams • Arrange atoms • Singular atom is usually in the center (often Carbon) • If no Carbon, least e- neg atom is in center • Hydrogen is always terminal • Find total # of e- available to bond (valence e- ), then divide by 2 to find available e- pairs • Place the bonding pairs between central atom and each terminal atom

  3. A. Drawing Lewis Diagrams • Determine remaining e- pairs – subtract # of bonds from #3 • Place lone pairs around terminal atoms (except H) to satisfy octet rule • Any remaining pairs are assigned to central atom • Determine whether or not central atom satisfies octet • If not, convert one or more lone pairs from terminal atoms to double or triple bonds • Certain atoms can be exceptions to octet rule – H, Be, B, S, P, Xe

  4. B. Drawing Lewis Diagrams • CF4 1 C × 4e- = 4e- 4 F × 7e- = 28e- 32e- + F F C F F 2 16 pairs of e- - 4 pairs of e- 12 pairs of e-

  5. A. Drawing Lewis Diagrams • CO2 1 C × 4e- = 4e- 2 O × 6e- = 12e- 16e- + OCO 2 8 pairs of e- -2 pairs of e- 6 pairs of e-

  6. B. 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

  7. B. Polyatomic Ions O O Cl O O • ClO4- 1 Cl × 7e- = 7e- 4 O × 6e- = 24e- 31e- + + 1e- 32e- 16 e- pairs - 4 e- pairs 12 e- pairs 2 =

  8. B. Polyatomic Ions H H N H H • NH4+ 1 N × 5e- = 5e- 4 H × 1e- = 4e- 9e- + - 1e- 8e- 2 = 4 pairs of e- -4 pairs of e- 0 pairs of e-

  9. C. Resonance Structures • Molecules that can’t be correctly represented by a single Lewis diagram • Actual structure is an average of all the possibilities • Show all possible structures separated by double-headed arrows

  10. O O S O O O S O O O S O C. Resonance Structures • SO3

  11. F F F S F F F F B F F H O H N O Very unstable!! D. 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)

  12. E. Drawing Lewis Diagrams • BeCl2 ClBeCl 1 Be × 2e- = 2e- 2 Cl × 7e- = 14e- 16e- + 2 8 pairs of e- -2 pairs of e- 6 pairs of e-

  13. E. Drawing Lewis Diagrams • SF6 1S× 6e- = 6e- 6F× 7e- = 42e- 48e- F F F S F F F + 2 24 pairs of e- - 6 pairs of e- 18 pairs of e-

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