- Hydrogen : Symbol H, the simplest element, with an atomic number of 1, colourless, and the lightest of all substances. Cavendish in 1706 was the first to recognise that it was an element. It is 14.4 times as light as air, and is found in a free state in volcanic regions. It can be obtained by the action of metals on acids, and forms an explosive mixture with air, burning with oxygen to form water. Commercially it is used to produce the very hot flame of the oxy-hydrogen blowpipe for cutting metals, to fill balloons and airships; to harden certain oils and render them suitable for margarine and soap production. The gas can be liquified, and the presence of the isotope deuterium was detected by Urey in 1931 in the residue of the evaporated liquid. The third isotope, tritium, is very rare.
- Helium : A gaseous element, no.2, symbol He, first discovered by means of the spectroscope in the Sun's atmosphere. The discovery, made in 1868 by the astronomer Sir Norman Lockyer, was followed in 1895 by Sir William Ramsay's proof that the element existed on earth. He found it in the Uranium ore, clevite. Later it was established that helium is formed by the radioactive decay of many elements which emit alpha-particles (neuclei of helium atoms) and is contained in all radioactive minerals. The largest source of helium is natural gas, the richest in helium being the gas from certain wells in Utah, USA. Next to hydrogen, helium is the lightest gas known, has a lifting power of 92% of hydrogen and the advantage that it is inert and non-flammable. It is used for inflating airships. Ordinarily air contains 1 part in 200,000 of helium. It was the last gaseous element to be liquified, this being achieved by Onnes in 1908 in Leyden. Liquid helium has many remarkable properties only imperfectly understood. As well as being scientifically fascinating it is indispensable in cryogenics as a medium for cooling other substances to near absolute zero. Hydrogen fusion in the 'H-bomb' produces helium.
- Lithium : A soft metallic element, no.3, symbol Li, and it is similar sodium. It is very reactive and is stored under paraffin oil. It is the lightest metal element.
- Beryllium : Metallic element, no.4, symbol Be. Very similar to aluminium, it is stronger than steel and only one-quarter its weight. It is not very abundant, its main source is the mineral, beryl. Copper containing 2 per cent beryllium is used for making springs. Because of its special properties the metal is used as a component in spacecraft, missiles and nuclear reactors. This accounts for its recent development on a technical scale. The metal powder is toxic.
- Boron : A metalloid element, no.5, symbol B. There are two forms, one crystalline, the other amorphous. It is not very abundant in nature but appears in concentrated deposits. It is best known as boric acid, which is used as a mild antiseptic (called boracic acid) and borax. Boron compounds are essential to some plants, e.g. beans. Used in the preparation of various special-purpose alloys, such as impact resistant steel. Compounds of boron and hydrogen are used as rocket fuels.
- Carbon : A non-matallic chemical element, no.6, symbol C, which occurs in chrystalline form as diamonds and graphite ; amorphous forms of carbon include charcoal and soot, while coke consists mainly of elementary carbon. The biochemistry of plants and animals largely hinges upon carbon compounds. The study of carbon compounds is called Organic Chemistry.
- Nitrogen : A non-combustible, gaseous element, no.7, symbol N, devoid of taste or smell and constituent of four-fifths of the atmospheric air. Nitrogen compounds are essential to plants and animals, and are used in fertilisers.
- Oxygen : It is the most abundant of all the terrestrial elements, no.8, symbol O. In combination, this gaseous element forms about 46% of the Earth's crust; one-fifth of the atmosphere; eight-ninths by weight of all water. Discovered independently by Scheele (c. 1773) and Pristley (1774). It is colourless, tasteless and odourless, and forms the chief life-supporting element of our world.
- Fluorine : Chemical element, no.9, member of the halogen family, symbol F, it is found in combination with calcium in fluorspar, and occurs in minute quantities in certain other minerals. Discovered by Scheele in 1771, it was first obtained by Moissan in 1886. A pale yellow gas, it is very reactive and combines with most elements except oxygen. Its acid, hydrogen fluoride, etches glass, the fluorine combining with the silicon to form volatile silicon fluoride. Organic fluorine compounds have found use as very stable polymers which resist a wide variety of chemical actions.
- Neon : Inert gas, element no.10, symbol Ne. It is present in air to the extent of 1 part in 65,000. The crimson glow produced when an electric discharge passes through the gas is familiar in advertising signs.
- Sodium : A metallic element, no.11, symbol Na (from Latin name Natrium), first obtained by Sir Humphrey Davy in 1807 from caustic soda by means of the electric battery. It's chloride is common salt; the deposits of salt (e.g. in Cheshire and at Stassfutr) have come into existence through the drying up of inland seas. Salt occurs in sea-water to the extent of about 3 per cent; the Dead Sea contains about 22 per cent. The blood of animals is maintained at a level of about 0.6% sodium chloride. That there is sodium in the Sun's atmosphere was confirmed in 1859 by Kirchhoff from his spectroscope observations. Liquid sodium metal has properties which make it suitable as a coolant in some neuclear reactors; a technique of handling this very reactive liquid has had to be developed.
- Magnesium : A metallic element, no.12, symbol Mg, first isolated in 1808 by Sir Humphrey Davy, who prepared it by electrolysing the chloride. Its chief ores are magnesite and dolomite. Industrially it is obtained by electrolysis. Many important light alloys contain magnesium. The metal burns with a very bright light, and for this reason it is used in photographers' flash bulbs and also in firework manufacture.
- Aluminium : Element no. 13, symbol Al, it is a light metal which conducts electricity well. It's specific gravity at 20oC is 2.705. Melting point of aluminium is 660.2oC. It is made commercially by electrolysing bauxite dissolved in cryolite (double fluoride of aluminium and sodium). Aluminium alloys are being increasingly used for construction purposes.
- Silicon : An important non-metallic element no. 14, symbol Si, it is related to carbon. Next to oxygen, it is the most abundant constituent of the Earth's crust (27% by weight). It occurs in many rocks, and oxide occurs in many forms (e.g. quartz, sand, flint, agate, chalcedony, opal etc). Principally used as a semi-conducting material for making transistors and similar devices. The circuitry of the computer is etched on a chip of silicon.
- Phosphorus : A non-metal element, no. 15, symbol P. Most familiar as a waxy, yellow solid which is spontaneously inflammable in air. It has chemical similarities to arsenic, like which it is very poisonous. It was discovered by Brandt in urine in 1669. It is found in most animal and vegetable tissues. It is an essential element of all plants and of the bones of animals. In combination with various metals it forms different phosphates, which are largely utilised as manures. The chief commercial use of phosphorus is in the preparation of matches.
- Sulphur : Element no. 16, it is a brittle, crystalline solid, symbol S, abounding in the vicinity of volcanoes. It is yellow in colour. It occurs in combination with other elements, as sulphates and sulphides, and allied with oxygen, hydrogen, chlorine, etc, it is of great commercial utility. Used in its pure state, it constitutes the inflammable element in gunpowder, it is also used for matches and for making sulphiric acid.
- Chlorine : A gaseous element, no. 17, symbol Cl, of the halogen family, first isolated in 1774 by Scheele by the action of manganese dioxide in hydrochloric acid. It unites easily with many other elements, the compounds resulting being termed chlorides. The gaseous element is greenish-yellow, with a pungent odour. It is a suffocating gas, injuring the lungs at a concentration as low as 1 part in 50,000, and was used during the First World War as a poison gas. Has a powerful bleaching action, usually being used in form of bleaching powder, made by combining lime and chlorine.
- Argon : Chemical element no. 18, symbol A. This was first of the inert gasses to be isolated from air by Rayleigh and Ramsay in 1804. Argon is used for filling gas-filled metal filament electric lamps. In gas discharge tube it gives a blue glow.
- Potassium : A metal, element no. 19, symbol K (from German Kalium). It is similar to sodium, reacting violently with water. It was discovered by Sir Humphrey Davy in 1807, and is now generally obtained by the electrolysis of fused potassium hydroxide or chloride/fluoride mixture. Its principal minerals are carnalite and kalnite, and it is relatively common in rocks, accounting for about 2.5% of the Earth's crust. An essential element for healthy plant growth; the ashes of plants are relatively rich in potassium.
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