 
Oxygen is a chemical element with an atomic number of 8. Oxygen forms a molecule O2 of two atoms which is a colourless odourless gas at normal temperatures and pressures. It is noncombustible, but will actively support the burning of combustible materials.Oxygen is very reactive, and is part of many common chemical compounds, such as water (H2O), carbon dioxide (CO2), carbon monoxide (CO), and sulphur dioxide (SO2). 
Oxygen is actually the second most abundant element making up the mass of the Earth; 32% of the mass of the Earth is iron, while a full 30% is oxygen. Much of this oxygen is bound up in silicate minerals, such as silicon dioxide, SiO2, which make up 90% of the Earth's crust. About 21% of Earth's atmosphere is oxygen. This hasn't always been the case, though. Early in our planet's history, the atmosphere had almost no oxygen. Oxygen from photosynthetic microbes eventually built up in the atmosphere, changing our planet's environment. 
Oxygen plays a critical role in respiration, the energy-producing chemistry that drives the metabolisms of most living things, which need oxygen to stay alive. Our own lungs are designed to extract oxygen from the air and use the blood to distribute it to our cells.Oxygen is generated during photosynthesis by plants and many types of microbes. Plants both use oxygen (during respiration) and produce it (via photosynthesis). Oxygen gas is soluble in water, which makes life in rivers, lakes and oceans possible. Oxidation involving combinations of atoms with oxygen occurs during fireworks displays, when metals tarnish or iron rusts, when compounds like hydrogen peroxide are used to clean wounds, and when fruits become brown and squishy. Electrolysis is a promising option for carbon-free hydrogen production from renewable resources. Electrolysis uses electricity to split water into hydrogen and oxygen. You can demonstrate this principle with a simple activity you can do yourself involving the electrolysis of water. Oxygen can also form a molecule of three atoms, which is known as ozone. Ozone in Earth's stratosphere plays a helpful role by blocking most of the harmful UV radiation from the Sun. |