1. Chapter 6-2
Lewis Structures (p. 208 – 209)

2. Drawing Lewis structures for molecules
1. Determine the total number of valence electrons in the molecule.
2. The atom with the lowest electronegativity is often the central atom (usually written first in the chemical formula). Arrange the other atoms’ symbols around the central atom.
3. Distribute eight electrons around each atom except hydrogen. If there aren’t enough e- to go around, form double or triple bonds.
4. Compare the number of valence electrons used in the structure with the number available from step 1.
5. Change each pair of dots that represents a shared pair of electrons to a single dash.

3. Resonance Structures
Molecules that can’t be correctly represented by a single Lewis diagram.
Actual structure is an average of all the possible structures.
Examples: O3 and SO3

4. Resonance Structures Consider the two ways to draw ozone (O3)
The two possible structures are separated by a double-headed arrow.

5. Resonance Structures
SO3 O
O S O O
O S O O
O S O