Chemistry Reference
In-Depth Information
of the molecule, the special way in which the hydrogen and oxygen atoms
are bonded to each other, as illustrated in Figure 85, which accounts for
the unusual behavior and properties of water.
The atom of oxygen in the molecule of water is bonded to the two of
hydrogen in such way that the angle between the two oxygen-hydrogen
bonds is under 180°. This means that the two atoms of hydrogen are
located just at one side of the oxygen, as illustrated in Figure 85. Although
the molecule has, overall, no net electric charge, the two hydrogen ends
of the molecule have slight positive electric charges, while the oxygen has
a feeble but definite negative charge. Molecules having separate positive
and negative electric charges are known as
polar molecules
, and it is the
polarity
of the water molecules that explains, for example, why water is
a good solvent of many substances. The opposite ends of the polarized
molecules of water also attract each other and form
intermolecular bonds
,
known as
hydrogen bonds
. The hydrogen bonds link between the mole-
cules and account, for example, for the relatively high boiling point of
water and for several other of its unusual properties.
FIGURE 85
Water.
A molecule of water is made up of two atoms of hydrogen
bonded to one atom of oxygen
(a)
. The three atoms in the molecule are not
aligned; because there are electrons on the oxygen atom (which are not involved
in the bonding between oxygen and hydrogen), the hydrogen atoms form an
angle, as shown in the figure. Since the electrons have negative electric charges,
they repel each other; moreover, their repulsive force coerces the hydrogen
atoms to come close together and form an angle of about 105° between them.
Molecules of liquid water are linked to each other by “hydrogen bonds”
(b)
; these
are weak attractive forces between the positively charged nuclei of the hydro-
gen atoms and the negatively charged electrons on the oxygen atoms. The dis-
tance between the hydrogen and oxygen atoms within each molecule are much
shorter and the bonding force between them much stronger than between
hydrogen-bonded molecules.
