Molecular Models Activity
carbon tetrachloride
ammonia
methane
hydrogen monochloride
water
trichloromethane
ethane
urea
ethyne
propane
dihydrogen monosulfide
butane
carbon dioxide
nitrogen triiodide (video)
supplies
Bonding and Shape of Molecules
Number
of Bonds
Number of
Unshared Pairs
0
3
0
4
0
3
1
2
2
Shape
Examples
-Be-
Linear
BeCl2
Trigonal planar
BF3
Tetrahedral
CH4, SiCl4
Pyramidal
NH3, PCl3
Bent
H2O, H2S, SCl2
B
C
:
2
Covalent
Structure
:
N
O:
Lewis Structures
1) Count up total number of valence electrons
2) Connect all atoms with single bonds
- “multiple” atoms usually on outside
- “single” atoms usually in center;
C always in center,
H always on outside.
3) Complete octets on exterior atoms (not H, though)
- no unpaired electrons (free radicals)
4) Check
- valence electrons match with Step 1
- all atoms (except H) have an octet; if not, try multiple bonds
- any extra electrons? Put on central atom
Carbon tetrachloride
Cl
Cl C Cl
Cl
CCl4
Cl
C
Cl
109.5o
Cl
Cl
Tetrahedral geometry
Carbon tetrachloride – “carbon tet” had been used as dry cleaning solvent
because of its extreme non-polarity.
Methane
H
HCH
H
H
C
H
109.5o
H
H
Tetrahedral geometry
Methane –The first member of the paraffin (alkane) hydrocarbons series.
a.k.a. (marsh gas, CH4).
Water
d(-)
SO2
Bent
geometry
O
H
H
d(+)
Polar molecule
Ethane
C = 1s22s22p2
H H
HC CH
H H
Lewis dot notation
ball-and-stick
C2H4
molecular formula
space-filling molecule
Ethane
H H
HC CH
H H
Lewis dot notation
ball-and-stick
C2H6
molecular formula
space-filling molecule
Ethyne
No octet
each C “feels” 6 electrons
HC CH
C2H2
HC CH
each C “feels” 7 carbons
Ethyne – a.k.a. “acetylene”
6 electrons = triple bond
HC CH
Stable octet
Dihydrogen monosulfide
SO2
S
H
H
Bent
Carbon dioxide
O C O
CO2
O
C
Linear
geometry
O
O C O
Ammonia
..
..
NH3
N
HH H
N
H
H
H
Trigonal
Pyramidal
geometry
N
H
107o
H
H
Amino Acids – Functional Groups
Amine
Base Pair
Carboxylic Acid
R- COOH
NH21lose H+
NH21-
H+
NH3
NH41+
1+
:
1-
:
:
H
N
N
N
H
H
amine
H
H
H
ammonia
H
H
H
ammonium ion
Hydrogen monochloride
H Cl
HCl
d(+)
d(-)
HCl(g) + H2O(l)  HCl(aq)
hydrogen
chloride
Polar molecule
water
hydrochloric
acid
Trichloromethane
d(+)
H
Cl C Cl
Cl
CHCl3
H
C
Cl
109.5o
Cl
Cl
Tetrahedral geometry
H
Cl C Cl
Cl
d(-)
Polar molecule
Urea
NOT “di-urea”
H
H
N
O C
N
H
H
H
H
N
O C
N
H
H
CO(NH2)2
Urea – The first organic compound to be synthesized (Wohler, 1828).
Propane
H H H
HC C CH
H H H
C 3H 8
H
H
C
H
H
C
H
C
H
H
H
Butane
H H H H
HC C C CH
H H H H
H H H
H-C-C-C-C-H
H H H
H
C4H10
H
H
C
H
H
H
C
H
H
C
H
H
C
H
H
Nitrogen triiodide
..
N
I
I
I
NI3
N
I
107o
I
I
Trigonal
Pyramidal
geometry
Video clip:
(slow motion)
detonation of NI3
Supplies







15 black
8 green
1 yellow
4 blue
4 red
42 hydrogen
67 bonds
(carbon)
(chlorine and iodine)
(sulfur)
(oxygen)
(nitrogen)
(hydrogen)
(bonds)
C
Cl
S
I
Cl
Cl C Cl
Cl
H
HCH
H
CCl4
CH4
HCl
CHCl3
H
O C O
H
Cl C Cl
Cl
H Cl
HC CH
C2H2
O N
CO2
S
H H
SH2
H H H H
HC C C CH
H H H H
N
H HH
H H H
HC C CH
H H H
N
I
I
I
Decomposition of Nitrogen Triiodide
Decomposition of Nitrogen Triiodide
N2
NI3
2 NI3(s)
I2
N2(g) + 3 I2(g)
H
H
..
..
C
N
O
109.5o
H
H
H
CH4, methane
lone pair
electrons
107o
H
H
104.5o
H
NH3, ammonia
H2O, water
..
O
O
O
O
O3, ozone
H
O
O
The VSEPR Model
The Shapes of Some Simple ABn Molecules
SO2
..
O
N
S
O
C
O
O
Linear
O
Bent
F
S
O
F
F
O
Trigonal
planar
Trigonal
pyramidal
AB6
F
F
F
Cl
F
F
T-shaped
F
F
F
Square
planar
Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 305
F
F
P
Xe
F
F
F
S
F
F
F
F
F
Trigonal
bipyramidal
Octahedral