Chapter 13
Molecular Shapes
Molecular Shape
• Molecular shape or molecular geometry
is the three-dimensional arrangement of
the atoms in a molecule.
Molecular Shape
• Molecular shape determines several
properties of a substance including:
– reactivity
– polarity
– phase of matter
– color
– magnetism
– biological activity
Olfaction – sense of smell
• Lock-and-Key Theory: humans can
smell various odors because each threedimensional odor molecule fits into only
one type of receptor.
Gustation – the sense of taste
• Taste receptors are
located on the tongue
and are sensitive to four
major tastes: salty,
sweet, sour and bitter.
• Taste receptors respond
differentially to the
varying shapes of food
and liquid molecules.
H2
H
2(1) = 2e-
H
Any 2 atoms
linear
What about molecules consisting of
more than two atoms
Five Molecular Shapes
See the table in your notes
Steps in Determining Molecular Shape
1. Draw the Lewis Structure for the
Molecule.
2. Count the number of atoms attached to
the central atom.
3. Count the number of lone pairs attached
to the central atom.
4. Use your counts on steps 2 and 3 to
determine the shape of the molecule.
H2S
2(1)+6 = 8e-
• Dihydrogen monosulfide or just hydrogen
sulfide is also known as sewer gas. This
colorless, toxic and flammable gas is
responsible for the foul odor of rotten eggs.
H
••
S
••
H
2/2
angular
H2S
• Dihydrogen monosulfide or just hydrogen
sulfide is also known as sewer gas. This
colorless, toxic and flammable gas is
responsible for the foul odor of rotten eggs.
S
H
H
Methane (CH4)
4 + 4(1) = 8e-
Methane (CH4)
4 + 4(1) = 8e4 atoms attached to the
central atom.
0 lone pairs on the
central atom.
4/0
Tetrahedral shape
Methane (CH4)
4 + 4(1) = 8e4 atoms attached to the
central atom.
0 lone pairs on the
central atom.
4/0
Tetrahedral shape
HCN
H
••
C••
1+4+5 = 10e-
••
N••
••
HCN
H
••
C••
1+4+5 = 10e-
••
N••
••
HCN
H
••
C••
1+4+5 = 10e-
••
N••
••
HCN
H
••
C
1+4+5 = 10e-
••
N••
HCN
H
••
C
1+4+5 = 10e-
••
N••
HCN
H
C
2/0
linear
1+4+5 = 10e-
••
N
H2S
S
H
H
2/2
angular
SO2
••
••
O
••
••
S••
6+2(6) = 18e-
••
••
O
••
SO2
••
••
O
••
••
S••
6+2(6) = 18e-
••
••
O
••
SO2
••
••
O
••
••
S••
2/1
angular
6+2(6) = 18e-
••
••
O
••
CH4
4/0
tetrahedral
NO3••
O
••
••
N
••
••
O
••
••
••
••
5+3(6)+1 = 24e-
O
••
NO3••
O
••
••
N
••
••
O
••
••
••
••
5+3(6)+1 = 24e-
O
••
NO3••
O
••
••
N
••
••
O
••
••
••
••
5+3(6)+1 = 24e-
O
••
NO3-
O
••
N
••
]
••
••
O
••
••
[
••
••
5+3(6)+1 = 24e-
O
3/0
trigonal
planer
SOCl2
What’s the shape of acetate?
4/0
3/0
tetrahedral
trigonal
planer
Homework
 Worksheet Chapter 13.