1. Lewis Structures
In Covalent Bonds valence electrons are distributed as shared or BOND PAIRS , and unshared or LONE PAIRS. • •• H Cl
shared or
bond pair
lone pair (LP)
This is called a LEWIS structure.

2. Steps for Building a Dot Structure
Ammonia, NH3
1. Add up the total number of valence electrons that can be used in your drawing.
Nitrogen: 1 atom x 5 valence electrons = 5 Hydrogen: 3 atoms x 1 valence electron = 3
Total = = 8 electrons (No More and No Less!)
2. Decide on the central atom; never H. Why?
If there is a choice, the central atom is the atom with lowest electronegativity.
Therefore, Nitrogen will be the center atom in this molecule.

3. Building a Dot Structure
Form a single bond between the central atom and each surrounding atom (each bond takes 2 electrons!) How many have we used so far? H N
4. Make Outside atoms happy first by adding remaining electrons as LONE PAIRS to complete the octet as needed (or duet in the case of H). H
• • N
Note that N has a share in 4 pairs (8 electrons), while H shares 1 pair (2 electrons).

4. Building a Dot Structure
Check to make sure there are 8 electrons around each atom. (except H) H should only have 2 electrons. This includes SHARED pairs. H
• • N
6. Check the number of electrons in your drawing with the number of electrons from step They must be the same. You may have to form double or triple bonds if you don’t have enough electrons.

5. Carbon Dioxide, CO2 1. Valence Electrons =
Carbon: 1 atom x 4 e- = 4 e- Oxygen: 2 atoms x 6 e- = 12 e- Total: 16 valence electrons
1. Valence Electrons =
2. Central Atom? = Lowest electronegativity?
3. Form bonds.
We’ve used 4 of the 16 total connecting atoms
4. Place lone pairs on outer atoms first How many did you use?
5. Check to see that all atoms have octets/stable configurations

6. Carbon Dioxide, CO2
6. The Carbon atom in the center does not have an octet. And we cannot add any more electrons, we only can use 18. So how does Carbon become stable? Carbon forms a double bond on both sides. That way it can have access to 8 valence electrons without adding any more total electrons.

7. Double and even triple bonds are commonly observed for C, N, P, O, and S
H2CO
SO3
C2F4

8. Now You Try One! Draw Sulfur Dioxide, SO2