1. Covalent Bonding & Lewis Structures
Octet Rule:
Atoms form bonds to obtain stable electron configurations…
8 e–’s in the outer shell like noble gases.

2. lone pair
nonbonded pair
unshared pair
1 shared pair
1 covalent bond
single bond:
1 pair of shared electrons

3. How many unshared pairs (lone pairs)?
structural formula:
shows the arrangement of atoms
How many unshared pairs (lone pairs)? 2

4. How many shared pairs? 3

5. N N O O Super Special Carbon C double bond: 2 pairs of shared e–’s
triple bond:
3 pairs of shared e–’s
N N
Super Special Carbon C
Carbon can form long chains because it forms up to 4 bonds on each C atom.
This allows large biomolecules to form such as:
proteins
lipids (fats)
carbohydrates (sugars/starches)
nucleic acids (DNA/RNA)

6. Drawing Lewis Structures
In 5 easy steps:
PCl3
Count
Connect
Octet
(if necessary)

7. Drawing Lewis Structures
Count valence electrons of all atoms in the polyatomic ion or molecule.
For anions (–), add e– ’s.
For cations (+), subtract e– ’s.
PCl3
(7) = 26

8. Drawing Lewis Structures
CONNECT atoms to the central atom with single bonds.
Central atom is the least electronegative (never H)
Keep track of the electrons:
26  6 = 20

9. Drawing Lewis Structures
OCTET
fill outer octets
Keep track of the electrons:
26  6 =  18 = 2

10. Drawing Lewis Structures
OCTET
fill central octet
Draw the Lewis structure for HCN
Keep track of the electrons:
26  6 =  18 = 2 2  2 = 0

11. Drawing Lewis Structures
If you run out of e–’s before the central atom has an octet…
…form multiple bonds until it does. (by removing lone pairs from outer atoms, more than likely…)

12. Drawing Lewis Structures
In 5 easy steps:
Count (val e–’s)
Connect (bonds)
Octet (outer dots)
Octet (central dots)
(if necessary)
form Multiple Bonds to fill central octet

13. O C O O C O Draw the Lewis structure for trichloromethane, CHCl3
Draw the Lewis structure for carbon dioxide, CO2
O C O
O C O

14. large, long chain biomolecules. nucleic acids carbohydrates
Quick Quiz!
1. Carbon atoms have 4 valence electrons to form up to 4 bonds. This allows carbon to form ______________ needed for life.
large, long chain biomolecules.
nucleic acids
carbohydrates
ALL of the above

15. Quick Quiz.
2. Which of the following diatomic molecules have a triple bond?
(hint: draw the Lewis structures) O2 N2
Br2 H2
O O
N N
Br Br
H H

16. Quick Quiz.
3. Draw the correct Lewis structure for dinitrogen monoxide , N2O (aka: nitrous or laughing gas)
hint: arrange the atoms as…
N N O
N N O