 In this video, we're going to investigate the properties of Oxygen. Oxygen has atomic number 8 and is found in group 16 of the periodic table. It has the chemical symbol O. Oxygen is of course a gas. It has no smell, colour or taste. But without it, we as humans would not be able to inhabit planet Earth. When cooled to very low temperatures, it will form a liquid and a solid, which are both pale blue. Oxygen makes up 21% of the Earth's atmosphere. It has taken many millions of years to make up this composition. Today's atmosphere seems to now have the perfect balance. You may want to check the history of the atmosphere for more details about this. Oxygen is used by the human body in a process called respiration. Take a deep breath in. Hold it for a few seconds. The air that entered your body has now been held in the lungs. Some of the oxygen you breathed in has been taken into the bloodstream and transported to parts of the body where it's needed. Respiration is taking place in the cells of your body. Oxygen combines with glucose, building up carbon dioxide and water. And releasing energy. This enables cells to function and our bodies to survive. As you breathe out, air now contains roughly 4% less oxygen than when you breathed in. This has been replaced by another gas called carbon dioxide. The oxygen in the atmosphere also affects our lives in other ways. It reacts chemically with a number of other materials. Oxygen will combine with reactive metals to form metal oxides. This is called corrosion. Most metal oxides are useful as they produce hard, protective layer. Aluminium oxide for example forms a protective layer on the surface of aluminium. This grey coating protects the body of the metal underneath from further corrosion. Modern aeroplanes have used this characteristic of aluminium as a choice of construction material. Iron III oxide is formed when iron reacts with water and oxygen and this is not useful. You will know iron oxide more commonly as rust. It makes the metal flaky and weak. The corrosion will eat into the metal which flakes off as the oxide is built up. There are ways of protecting iron from oxidation. Putting oil on your bike chain for example. It will protect it from the rust and keep it strong. Oxygen can be produced in the lab by the chemical decomposition of hydrogen peroxide. If the earth's atmosphere consisted of 30% oxygen rather than 21% forest fires would start with lightning and would never go out. Life as we know it would be impossible.