ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Chlorine and oxygen. Gas jars filled with chlorine (Cl2, left) and oxygen (O2, right) gases. These gaseous chemical elements are made up of diatomic molecules. Chlorine has a faint green colour, and is a toxic gas. It is used in the chlorination of water as a disinfectant. Oxygen is a reactive gas that is essential to life. It fuels reactions like the rapid combustion seen in fires, and also the slower reaction of respiration, the use of oxygen to fuel body metabolism. Oxygen makes up a fifth of the atmosphere by volume. Chlorine is obtained from seawater where it is present in salt (sodium chloride).
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