Covalent Bonding & Lewis Structures
Octet Rule:
Atoms form bonds to obtain stable electron
configurations…
8 e–’s in the outer shell like noble gases.
lone pair nonbonded pair
unshared pair
1 shared pair
1 covalent bond
single bond:
1 pair of
shared e–’s
structural formula:
shows the arrangement of atoms
How many unshared pairs?
2
How many shared pairs? 3
double bond: O O
2 pairs of shared e–’s
triple bond: N N
3 pairs of shared e–’s
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)
Drawing Lewis Structures
In 5 easy steps:
PCl3
1.
2.
3.
4.
5.
Count
Connect
Octet
Octet
(if necessary)
Drawing Lewis Structures
PCl3
5 + 3(7) = 26
1. COUNT valence e–’s of
all atoms in the molecule.
Drawing Lewis Structures
2. 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
Drawing Lewis Structures
3. OCTET
fill outer octets
Keep track of the electrons:
26  6 = 20
20  18 = 2
Drawing Lewis Structures
4. OCTET
fill central octet
Keep track of the electrons:
Draw the Lewis
structure for
HCN
26  6 = 20
22=0
20  18 = 2
Drawing Lewis Structures
5. If you run out of e–’s
before the central atom
has an octet…
…form multiple bonds
until it does.
Drawing Lewis Structures
In 5 easy steps:
1.
2.
3.
4.
5.
Count (val e–’s)
Connect (bonds)
Octet (outer dots)
Octet (central dots)
(if necessary)
form Multiple Bonds
to fill central octet
Draw the Lewis structure for trichloromethane,
CHCl3
Draw the Lewis structure for carbon dioxide,
CO2
O
C
O
O
C
O
Quick Quiz!
1. Carbon atoms have 4 valence electrons
to form up to 4 bonds. This allows carbon
to form ______________ needed for life.
A. large, long chain biomolecules.
B. nucleic acids
C. carbohydrates
D. ALL of the above
Quick Quiz.
2. Which of the following diatomic
molecules have a triple bond?
(hint: draw the Lewis structures)
A. O2
O
O
B. N2
N
N
C. Br2
Br
Br
D. H2
H
H
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