Page 8 - Curriculum Visions Dynamic Book

(Above) The ice shelves around Antarctica and Greenland are simply thick slabs of ice floating on water. They act as a protective blanket for the water underneath.
Physical properties of water
Many of the properties of water are very unusual and some quite unique. For example, although most solids are more dense than their liquids, ice is less dense than liquid water. That is why ice cubes float in a glass of water. Liquid water is most dense at 4°C, not at its freezing point, as is the case for other liquids.
Many such properties are vital to the way our world works, the way that water is used by living things, and the way we use water in homes and factories. For example, if ice did not float but was heavier than liquid water, it would sink to the bottom of a lake as soon as it formed on the surface. In cold conditions more and more water would turn to ice and sink, and eventually the lake would fill with ice. This ice would also be very slow to melt because it would be protected from warmth by a layer of surface water. Under these conditions the Great Lakes, for example, would be the Great Ice Blocks.
Water-living creatures also depend on ice floating. The ice forms a protective blanket on the surface of the lake. At the same time, as water cools to 4°C, it sinks to the bottom of the lake. In this way, except
in the most unusual of circumstances, although the surface of a river, lake, or ocean freezes, the bottom stays unfrozen and provides a sheltered home to living things.
The nature of water molecules
Many of the properties of water outlined above are the result of the special nature of water molecules. Water, or hydrogen dioxide, consists of two hydrogen atoms bonded to one oxygen atom. That is why it is represented by the formula H2O. As it happens, this linking of hydrogen and oxygen leaves both hydrogen atoms on one side of the molecule and the oxygen on the other side. The atoms are bonded at an angle of about 104 degrees. The hydrogen atoms are attached to the oxygen by covalent bonds.
(Above) If water did not have the strange property of being lighter as a solid than a liquid, then ice fishing would not be possible.
8