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April 1, 2012

Oxygen is a radical, a rebel, an emotionally unstable element with a crazed look in its eye. Oxygen, named by Antoine Lavoisier after the Greek ‘begatter of acids’ in the mistaken belief it was a component of all acids, is part of the Chalcogen family (group 16 in the periodic table). The whole Chalcogen family is a bit odd from top (oxygen) to bottom (polonium) but oxygen is unhinged in a way that makes all the others slowly shake their heads in disbelief. Oxygen was independently discovered by Joseph Priestly (theologian, legendary chemist and staunch defender of the phlogiston theory) and Carl Wilhelm Scheele (indirect poisoner of thousands through the arsenic-based pigment ‘Scheele’s Green’ used in wallpaper, toys and clothes throughout 18th century Europe, his habit of sniffing and tasting any new compound contributed to his early death).

Without oxygen nothing burns

Oxygen is the third most abundant element in the universe, the most abundant element on Earth by weight and the largest proportion of our bodies by weight. To make a human requires a spectacular array of compounds made up of around 60 different elements. Deficiencies of any of these elements causes health problems and disease but a lack of oxygen will kill you in minutes.

Oxygen has two forms. The most common form is a pair of oxygen atoms O2. This colourless, tasteless gas makes up 20% of the air we breathe. O2 is unusual by any standards. The six electrons in the outer shell of each of the two atoms combine is such a way to result in one lonely electron on each atom (known as a free radical). Electrons hate being on their own and will go out of their way to find a partner to the extent that they will kidnap electrons from other pairs. Having two free radical electrons on one O2 molecule gives oxygen its manic qualities. O2 will react with almost anything it bumps into to kidnap an electron and this is blandly referred to as oxidation. In practice oxidation can mean oxygen combining with food we have eaten to give us energy, to clothes fading through oxidation of dyes, rust through oxidation of metals and explosions through (rapid) oxidation of fuels.

Another curious feature of having two free radical electrons is that O2 is paramagnetic meaning that when in a magnetic field O2 also becomes a magnet. Liquid O2 (formed at -183 degrees Celsius) will form a liquid bridge between the two poles of a horse-shoe magnet. Before rushing out to try this yourself please note the beautiful pale blue liquid O2 is a more concentrated form of the gas. Something that burns in air becomes explosive when soaked in liquid O2. The memory of a liquid O2 soaked hob-nob biscuit burning and spinning like a Catherine-wheel will live with me for a long time.

It is only through photosynthesis that such a reactive element can be so abundant in our atmosphere. Without plants, bacteria and algae producing oxygen for us to breath all the oxygen in the atmosphere would have reacted with elements in the earth long ago and life on this planet would have taken a very different evolutionary path.

Another form of oxygen is ozone or O3. Formed by high energy UV light hitting the upper reaches of our atmosphere. Ozone is an even more reactive form of oxygen and makes O2 look calm and well adjusted by comparison. In the upper atmosphere ozone protects us from cancer causing UV light by absorbing most of the radiation before it reaches us on the ground. At ground level ozone becomes more troublesome. It is formed by UV light reaching ground level on sunny days and as a bi-product in car exhausts. Ozone has a distinct chlorine bleach smell and its highly reactive nature means it damages our lungs when breathed in. O3 has been linked to asthma attacks and other severe respiratory problems and is considered a pollutant at ground level.

Tune in next week for frightening fluorine.


Images by @SciCommStudios

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