A level Biology exam revision resources written by A level Examiners


Water has the chemical formula H2O , it is a simple inorganic compound and is essential for all living organisms. The fact that there is plenty of water on earth, is one of the reasons why the Earth can support living organisms.

Many of the unique properties of water are caused by its ability to form hydrogen bonds. These bonds can form because water molecules are polar (see figure 1), meaning they have a positive and a negative end. As a result there are attractive forces between adjacent water molecules. This can be seen in figure 2 below.

Figure 1 : The polar nature of water

POlar nature of water

Figure 2 : H-bonding in water


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