|
8. OxygenName: Oxygen
Oxygen is a Group 16 element. While about one fifth of the atmosphere is oxygen gas, the atmosphere of Mars contains only about 0.15% oxygen. Oxygen is the third most abundant element found in the sun, and it plays a part in the carbon-nitrogen cycle, one process responsible for stellar energy production. Oxygen in excited states is responsible for the bright red and yellow-green colours of the aurora. About two thirds of the human body, and nine tenths of water, is oxygen. The gas is colourless, odourless, and tasteless. Liquid and solid oxygen are pale blue (see picture above) and strongly paramagnetic (contains unpaired electrons). Ozone (O3) is another allotrope of oxygen. It is formed from electrical discharges or ultraviolet light acting on O2. It is an important component of the atmosphere (in total amounting to the equivalent of a layer about 3 mm thick at ordinary pressures and temperatures) which is vital in preventing harmful ultraviolet rays of the sun from reaching the earth's surface. Aerosols in the atmosphere have a detrimental effect on the ozone layer. Large holes in the ozone layer are forming over the polar regions and these are increasing in size annually. Paradoxically, ozone is toxic! Undiluted ozone is bluish in colour. Liquid ozone is bluish-black, and solid ozone is violet-black. Oxygen is very reactive and oxides of most elements are known. It is essential for respiration of all plants and animals and for most types of combustion. Oxygen was discovered by the Swedish pharmacist Carl Wilhelm Scheele in 1771, but this discovery was not immediately recognized, and the independent discovery by Joseph Priestley on August 1st 1774 was more widely known. It was named by Antoine Laurent Lavoisier in 1774. The systematic element name for oxygen is octium. Oxygen can be toxic at elevated partial pressures. Certain derivatives of oxygen, such as ozone (O3), hydrogen peroxide, hydroxyl radicals and superoxide, are also highly toxic. The body has developed mechanisms to protect against these toxic species. For instance, the naturally-occurring glutathione can act as an antioxidant, as can bilirubin which is normally a breakdown product of hemoglobin. Highly concentrated sources of oxygen promote rapid combustion and therefore are fire and explosion hazards in the presence of fuels. This is true as well of compounds of oxygen such as chlorates, perchlorates, dichromates, etc. Compounds with a high oxidative potential can often cause chemical burns. Quick links
|