Chemistry Reference
In-Depth Information
H
H
C
H
H
the methane molecule is tetrahedral
H
109.5°
C
H
H
H
a
Methane molecule.
b
Model of the methane molecule. The tetrahedral shape is caused by the
repulsion of the C-H bonding pairs of electrons.
Figure 3.23
Ammonia
is a gas containing the elements nitrogen
and hydrogen. It is used in large amounts to make
fertilisers. The electron configurations of the two
elements are:
Water
is a liquid containing the elements hydrogen
and oxygen. The electronic structures of the two
elements are:
8
O 2,6
1
H 1
The oxygen atom needs two electrons to gain the
electron configuration of neon. Each hydrogen
requires one more electron to gain the electron
configuration of helium. Again, the oxygen and
hydrogen atoms share electrons, forming a water
molecule with two single covalent bonds as shown
in Figure 3.26. A water molecule is V-shaped
(Figure 3.27).
7
N 2,5
1
H 1
The nitrogen atom needs three more electrons
to obtain the noble gas structure of neon. Each
hydrogen requires only one electron to form the
noble gas structure of helium. The nitrogen and
hydrogen atoms share electrons, forming three
single covalent bonds (Figure 3.24). Unlike methane
the shape of an ammonia molecule is pyramidal
(Figure 3.25, p. 48).
H
H
N
H
N
H
H
H
nitrogen atom
3 hydrogen atoms
ammonia molecule (NH
3
)
Figure 3.24
Formation of ammonia.
