Page 4 - Curriculum Visions Dynamic Book

An element is a substance that cannot not be decomposed into a simpler substance by any known means. Each of the 92 naturally occurring elements is therefore one of the fundamental materials from which everything in the Universe is made. This book is about oxygen.
Oxygen
Oxygen is the most common element by volume or mass (weight) on Earth. In each breath you take, one- fifth of the molecules are oxygen; there are twelve trillion tonnes of oxygen in the air. Yet despite the fact that it is so common, we are hardly aware of this vital element because oxygen is transparent, it has no colour, taste or smell.
Oxygen occurs uncombined (as one of a mixture of gases) in air, but it also readily combines (reacts) with a wide variety of other elements to make compounds. Indeed, oxygen is among the most reactive of all the elements. For example, nearly
all the rocks of the Earth are compounds containing oxygen. Water is also a compound of oxygen along with hydrogen.
Oxygen is vital for life. When oxygen reacts with
a fuel, the fuel is oxidised and becomes an oxide, sometimes turning into a solid, in other cases forming a gas such as carbon dioxide. This reaction – called burning – releases heat energy.
The reaction of oxygen with fuels such as coal, oil and natural gas can also be harnessed to convert the chemical energy in the fuel into movement energy. This is how we power many of our machines.
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