1. Table 2.1 Lewis structures of some common moleculesMolecule Lewis structures* H2H2 N 2, CO O 3, SO 2,NO 2 - NH 3, SO 3 2- C O PO 4 3-, SO 4 2-, ClO 4 - HH N N O O O S O O N O O N H HH 2- S O O O P O OO 3- O P O OO 2- O Cl O OO - O coordinate covalent

2. Formal Charge (F.C.)

3. Oxidation number of an element What is the oxidation number of (a) nitrogen in the azide ion, and (b) manganese in the permanganate ion, (a)3 x O.N(N) = -1. O.N.(N) = (b)O.N.(Mn) + 4 x O.N.(O) = -1 O.N.(Mn) = -1-4x(- 2) = +7.

4. Reson ance In fact these are called the the resonance structures of the carbonate oxyanion.

6. Reson ance

7. The BF 3 molecule, for instance, is a resonance structures Resonance has two man effects: 1. Resonance averages the bond characteristics over 2. Resonance reduces the energy of the molecule any single contributing structure.

8. Write resonance structures for the NO 2 F molecule and identify the dominant structures.

9. Write resonance structures for the ion. :

10. Hypervalent compounds. : SF 6, PCl 5,

11. Dative covalent bond. Stoichiometry of covalent molecules In this way the stoichiometry of covalent molecules is determined by the number of valence electrons available for sharing and forming two electron pairs.