Introduction
Do you know that we have a use for water in all of its three
forms. We drink water in liquid form, we put ice or water as a solid into our
drinks, and we inhale gaseous water as part of the air we breathe.
There are very few substances on the surface of the Earth
that can be found naturally in these three states or forms, that is as liquid,
solid and gas. Water is one of these remarkable substances. This is one of
water’s most unique properties.
Another very unique property of water is that, when it is a
solid it floats on its liquid. This is a very rare thing, usually the solid of
any substance when placed in a container of the same substance in the liquid
state will sink to the bottom of the container. This is because the solid of
nearly all substances is denser than the liquid, but so for water.
Obviously water has something special going on its chemical
nature and this is what this and the next few posts are about.
Ice Floats on Water
The following excerpt has been taken from the book “The Water
Planet”, published by the National Geographic Education Division, D.C.
“Effects of Bonding
The polarity of water molecules makes water great for dissolving other
substances, such as sea salts and substances that travel through your body.
Polarity also means that ice will float on liquid water. As water freezes, the
weak bonds between the molecules form an open arrangement of molecules, as seen
in Figure 7.
The molecules,
therefore, are farther apart when they are frozen than they were as liquid.
This causes ice to have a lower density than liquid water, letting it float on
water. In large bodies of water, floating ice prevents the water below from
freezing. If lakes froze from the bottom up, they would freeze solid every winter,
killing all living things inside.”
Conclusion
The reason why ice or solid water floats on liquid water is
due to the way water molecules bond when they are a solid. They bond in such a
way that the molecules spread out making the solid (ice) less denser. Notice
that when you freeze water it expands, if it were to contract it would
certainly not float on liquid water.
The diagram shows this quite clearly.
This marvellous polarity property of water allows life to
continue in winter. If the water molecules did not have this property then
lakes and rivers would freeze all solid.
The more we look at water, we really come to realise that it
is just perfect to support and maintain life the way we have it right now. If
we were to change water we would change life the way we now it now.
End (15).