My Science School

OXYGEN

We cannot see, smell or taste oxygen. Yet it forms one-fifth of air and is vital for life. We must breathe oxygen to stay alive. So must all animals and plants.

Oxygen is one of the commonest chemical elements on Earth. It forms about half the weight of the planet’s hard outer rock layer or crust. It makes up one-fifth of the air. Joined with hydrogen it forms the water which covers more than two-thirds of Earth’s surface.

Oxygen is a vital part of chemical changes inside each microscopic living cell, which break apart food substances to obtain the energy for life. This is why oxygen is essential for all living things (except for a few specialized types of microbes).

Oxygen is also needed for burning. A substance such as coal or wood burns by splitting apart and joining with oxygen to form new substances. It quickly gives out lots of heat and often light in the process. This is known as combustion (burning).

            Substances burn by joining with oxygen and giving out energy as heat and light. The welding torch burns acetylene gas.

HYDROGEN

The most abundant element in the Universe is hydrogen. It forms the bulk of most stars. On Earth, most hydrogen (chemical symbol H) is joined to oxygen (O) to form water (H2O). Hydrogen is also the simplest and lightest chemical element because each of its atoms has only two sub-atomic particles, one proton and one electron.

Hydrogen joins with carbon to form the substances known as hydrocarbons. Many of the fuel gases obtained from natural gas or crude oil, such as propane and butane, are hydrocarbons. Hydrogen also joins with carbon and oxygen to form carbohydrates. Starches in foods like potatoes and rice, and sugars in cane or beet, are carbohydrates.

            Pure hydrogen gas is much lighter or less dense than air. It filled the great airships of the early 20th century to keep them aloft. However hydrogen also burns very easily. After several disasters where airships caught fire, hydrogen was no longer used. Today airships use another light gas, helium, which does not burn.

            The Sun and other stars are mostly made of hydrogen. In the star’s centre, tremendous temperatures and pressures squash hydrogen atoms together to form atoms of the gas helium. As this happens, huge amounts of energy are released as heat and light. The energy travels up to the Sun’s glowing surface and then passes through space to Earth. This is known as nuclear fusion because the centres, or nuclei, of the hydrogen atoms join or fuse together. Nuclear energy on Earth is obtained by splitting nuclei apart, known as nuclear fission.