1. Covalent Bonds
Covalent bond is a bond formed when 2 electrons are shared between atoms
H + H forms H2
Lewis Structure of H2
Lewis Structure of F2
A lone pair is any electrons not shared in a covalent bond (a.k.a nonbonding electrons)

2. Drawing Lewis Structures
Follow the octet rule - an atom wants to have 8 valence electrons.
CH4 H2O

3. Rules for Drawing Lewis Structures Example CCl4
1. Count total number of valence electrons from all atoms plus electrons from charge of molecule
C = e
4Cl = 4x7= 28 e
charge = e
32 total e
2. Set the least electronegative non-H atom at the center
C is 2.6
Cl is 3.2 C

4. Rules for Drawing Lewis Structures
3. Place other atoms around it with a bond connecting each atom to the central atom
(1 bond = 2 electrons)
4. Put any remaining electrons around atoms as lone pairs or double bonds to make octet • Cl
32 total e
- 8 bonding e
24 nonbonding e
24e /2 = 12 lone pairs • • C •

5. Rules for Drawing Lewis Structures
5. Check Structure with Formal Charge
F.C. = # original electrons - #bonds - 2(# lone pairs)
F.C = 0 is best, but close to zero (+1, -1) is acceptable •
F.C. C = 4 original e
- 4 bonds
- 2(0) loan pairs.
Carbon good Cl • • C
F.C. Cl = 7 original e
- 1bonds
- 2(3) lone pairs
Chlorine 0 good Cl • • • Cl C Cl • • • • • Cl • •

6. Rules for Drawing Lewis Structures
CO2
ClO4-
NF3

7. Group Work Draw the Lewis structures of the following H2O PCl3 CS2
NO3-
IF3