THE CHEMICAL ELEMENTS

No element has been found in the stars or in space which does not occur on the Earth. But when were the elements first discovered on Earth? From ancient times up to the middle of the seventeenth century only 11 elements were known to man – antimony, arsenic!, carbon, copper, gold, iron, lead, mercury, silver and sulphur. The first element to be discovered in "modern times" was phosphorus, in 1669. The next discovery was cobalt and platinum in 1735, followed by zinc (1746), nickel (1751), bismuth (1753), magnesium (1755), hydrogen (1766), fluorine (1771) and nitrogen (1772). In 1774 Lavoisier discovered oxygen. He called it "eminently breathable air". Chlorine and manganese were also discovered in 1774, which year can be looked upon as the annis mirabilis of Chemistry. Chemistry was very much a French science in those days. In the year of the French Revolution, 1789, uranium was discovered.

Largely due to the knowledge gained from John Dalton’s Atomic Theory of 1802 and his laws of multiple and constant proportions, whereby atoms combine in whole numbers, no less than 13 elements were discovered between 1801 and 1811. Silicon, the basic element of the rocks, was discovered in 1823, and aluminium in 1827 – the first element to be discovered electrolytically.

Helium was discovered by William Ramsay in 1894, twenty-six years after it was discovered in the Sun by N. Lockyer in 1868. From 1898 onwards the unstable radioactive elements came on the scene. By 1925, the last of the stable elements, rhenium was discovered.

Abundance of the elements

If silicon is taken as standard, then for every 10⁶ atoms of silicon, only four elements are more abundant on Earth, namely : hydrogen 3,18 x 10¹⁰, helium 2,21 x 10⁹, oxygen 2,14 x 10⁷ and carbon 1,18 x 10⁷. Nitrogen 3,64 x 10⁶ and neon 3,46 x 10⁶ are slightly more than three times as abundant as silicon. The abundance of magnesium is equal to that of silicon. Slightly less abundant are aluminium 8,5 x 10⁵, iron 8,3 x 10⁵, sulphur 5 x 10⁵, argon 1,17 x 10⁵, followed by calcium 7,2 x 10⁴, sodium 6 x 10⁴, nickel 4,8 x 10⁴ and calcium 1,27 x 10⁴. Then follow elements whose abundance is less than 10 000 compared to silicon’s 1 000 000, namely phosphorus 9600, manganese 9300, chlorine 5700, potassium 4205, titanium 2770 and fluorine 2450. The next 11 elements in order of abundance have abundances of 1000 to 10. Nineteen occur with abundances between 10 and 1. The highest fractional abundances are silver 0,45, and mercury 0,4. They are thus twice as abundant as gold 0,2 as against every 1 000 000 silicon atoms.

The most abundant of the radioactive elements is thorium with an abundance of 0,058, followed by uranium 0,026. The latter two elements are much more abundant on the Moon so that sooner or later settlements on the Moon will have to be set up to keep up the supplies of these radioactive elements. And when the Moon’s supplies of thorium and uranium peter out, we shall have to look elsewhere. Mars may be a good stand-by but Venus is out, because of its high surface temperature of 450° Celsius. Mercury’s rate of rotation is 58 days. Any point on its surface, therefore, has 29 days of continuous sunshine during which time it must get inordinately hot. In a few thousand years’ time, therefore, man will be hard put to maintain his supplies of radioactive fuels. There will be no point in trying to obtain radioactive fuels from planets of the nearby stars because a one-way trip to Alpha Centauri will encompass at least 17 years. Think of the food that will have to be lugged along and the fuel for the return journey. And it’s no good trying to speed up the rate of travel because of the danger of collisions with dark objects on the way. If you travel at one-half the speed of light, your radar waves reflected from an object on your line of motion will reach you at the very moment you make the collision. Therefore, man will have to settle for a speed of not more than one-quarter of the speed of light, namely 75 000 kilometres per second. Think of the engines required to generate such a speed – almost 5 000 times the speed of Voyager-2 during the Grand Tour of the Planets.

Besides the 92 naturally occurring elements, 11 transuranian elements have been synthesised in the great accelerators: no. 93 neptunium, 94 plutonium, 95 americium, 96 curium, 97 berkelium, 98 califormium, 99 einsteinium, 100 fermium, 101 mendelevium, 102 nobelium and 103 laurencium,. These atoms exist only for fleeting moments before they decay and cannot be accumulated or stored.

Eben van Zyl

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TELESCOPES FOR SALE

Meade LX200 10"

Starbase CD Rom Pc Drive Function, Extra lenses and filters, large case dust proof. R18000,00 Neg. To be sold end Feb. Contact: Mauro on 814-3108 A/H or Marianne on 624-1400 O/H

1994 Model Vixen Super Polaris Telescope

1000mm Focal Length, full equatorial mount with extendable tripod, fully equipped attachment console including:

3 X High Power Lenses (10x, 50x 500x), Sun and moon filters, Star diagonal prism, Night light, Electronic Pathfinder for star tracking, Finder scope, Refractor tube with optimal quality glass mirror, Slow motion Controls for Altitude and Latitude, Oil level for optimal positioning ability, Weighted tube for perfect motion control adjustments. Contact Calvin - tele: (011) 837-9139, fax: (011) 837-0018. (Seller: Brendan Chidrawi). Price R6000,00 - R6500,00

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