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Properties of water
71% of the Earth is covered by water and 97% of this water is in the oceans. Water is made up of two atoms of hydrogen and one atom of oxygen. Because of water’s electronic structure, the oxygen atom has a slight negative charge on it and the hydrogen atoms are slightly positive. When water molecules are close together, their positive and negative regions are attracted. These attractive forces are known as hydrogen bonds. Hydrogen bonds are the reason for water’s very special properties which make life on Earth possible.
Density is a measure of how compact a substance is. It is defined as the mass of a substance divided by its volume. Solids are almost always the most dense form of a substance, then liquids and then gases. As temperature increases, the density generally decreases. Pure water is an exception to this and is the only substance which has its highest density as a liquid. Water is at its most dense at about 4 oC. This is because hydrogen bonds between water molecules give ice a very stable open ordered structure. At low temperatures, water has a higher density than ice and this means that ice floats.