Hannah Morgan, University of Bristol, firstname.lastname@example.org
The Water Cycle
Water in a Pool
Water is one of the most common compounds on Earth. It makes up around 71% of the Earth's surface. It is a compound of hydrogen oxide, H20, with a molar volume of 18mg/l. Water is a clear, colourless, odourless liquid. A human can only survive for a matter of days without it.
This is a diagram showing the structure of water: the oxygen is in red, the hydrogen in grey.
Water is a polar molecule, the diagram below shows the regions of positive and negative charge on a water molecule.
As water is polar, it interacts with other molecules by hydrogen bonding.
This diagram shows the differences in bond lengths between molecules.
The difference in polarizability in the molecule leads to attraction of other hydrogen molecules to an oxygen atom.
This diagram shows the regions of charge surrounding two water molecules, and the dotted line represents a hydrogen bond.
Sometimes water gives the appearance of being blue, this is because light is attenuated as it passes through, the blue wavelengths are attenuated least and so are reflected from the bottom of pools for example, this results in the blue colour.
Does water come straight from the tap?
Water itself does not come from the tap, but its origin is part of a simple cycle called the water cycle. This has to meet different standards to water used for other uses. There is a saying that water flowing down the River Thames has been drunk by eight people before in its life. This is probably true. There is only a finite supply of water on Earth, but it has its own natural cycle which enables us to drink it whenever we like!