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Radioactive Red

April 2nd, 2009 admin No comments

Radioactive Red

How Rare and Inert are the Noble Gases?

Elements of group 18 of the present day periodic table are now collectively known as Noble Gases as they are the most stable gaseous elements due to the fact that they not only have the maximum number of valence electrons that their outer shell can hold, but also they rarely react with other elements, and are used in many conditions when a stable element is needed to maintain a safe and constant environment. As their name ‘Rare gases’ suggests, the noble gases are rather uncommon on Earth. Collectively, they make up about 1 percent of Earth's atmosphere. Most of the noble gases have been detected in small amounts in minerals found in Earth's crust and in meteorites. They are thought to have been released into the atmosphere long ago as by-products of the decay of radioactive elements in Earth's crust.

Of all the rare gases, namely: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), argon is present in the greatest amount. It makes up about 0.9 percent by volume of Earth's atmosphere. The other noble gases are present in such small amounts (there are only 5 liters of helium in every million liters of air) that it is usually more convenient to express their concentrations in terms of parts per million (ppm). But contrary to it, helium is much more abundant in the outer space. In fact, next to hydrogen, helium is the most abundant element in the universe. About 23 percent of all atoms found in the universe are helium atoms.

Though Radon is present in the atmosphere in only trace amounts, higher levels of radon have been measured in homes All Over the United States. It can be released from soils containing high concentrations of uranium, and they can be trapped in homes that have been weather sealed to make heating and cooling systems more efficient. Radon testing kits are commercially available for testing the radon content of household air. Most of the rare gases are obtained commercially from liquid air. As the temperature of liquid air is raised, the rare gases boil off from the mixture at specific temperatures and can be separated and purified. Although present in air, helium is obtained commercially from natural gas wells where it occurs in concentrations of between 1 and 7 percent of the natural gas.

All the noble gases are colorless, odorless, and tasteless. They exist as monatomic gases, which mean that their molecules consist of a single atom. The boiling points of the noble gases increase in moving down their group in the periodic table. Thus Helium has the lowest boiling point of any element and it has no melting point because it cannot be frozen at any temperature. The most important chemical property of the noble gases is their lack of reactivity. Helium, neon, and argon have not been found to combine with any other elements to form compounds as yet. It has been only in the last few decades that some compounds of the other rare gases have been prepared. In 1962 English chemist Neil Bartlett succeeded in preparing a compound of xenon, xenon platinofluoride (XePtF6), as the first compound of a noble gas. Since then, many xenon compounds containing mostly fluorine or oxygen atoms have been prepared. Krypton and radon have also been combined with fluorine to form simple compounds. Because some noble gas compounds have powerful oxidizing properties, they have been used to synthesize other compounds. The low reactivity of the noble gases can be explained by their electronic structure. The atoms of all six gases have outer energy levels containing eight electrons, the arrangement that chemists believe the most stable arrangement an atom dreams to have. Because of these very stable arrangements, noble gas atoms have little or no tendency to gain or lose electrons, which they would have to do in order to take part in a chemical reaction.

As is the case with all substances, the uses to which the noble gases are put reflect their physical and chemical properties. For example, helium's low density and inertness make it ideal for use in lighter-than-air crafts. Moreover, because of the element's very low boiling point, it has found many applications in low-temperature research and technology. Divers breathe an artificial oxygen-helium mixture to prevent the formation of gas bubbles in their blood as they swim to the surface from great depths. Other uses for helium have been in supersonic wind tunnels, as a protective gas in growing silicon and germanium crystals and, together with neon, in the manufacture of gas lasers.

Neon is well known for its use in neon signs. Glass tubes of any shape can be filled with neon. When an electrical charge is passed through the tube, an orange-red glow is emitted. By contrast, ordinary incandescent light bulbs are filled with argon. Because argon is too inert to react with the hot metal filament and prolongs the bulb's life. Argon is also used to provide an inert atmosphere in welding and high-temperature metallurgical processes. By surrounding hot metals with inert argon, the metals are protected from potential oxidation by oxygen in the air. Krypton and xenon also find applications in commercial lightings. Krypton can be used in both incandescent light bulbs and fluorescent lamps, both of which are also employed in flashing stroboscopic lights that outline commercial airport runways. And because they emit a brilliant white light when electrified, they are used in photographic flash equipment. Radon has registered its applications in medical -radiotherapy due to its radioactive nature. Ar is used for optical and mass spectrometry as the plasma gas. Other noble gases are used for plasma spectrometry including the for improved detection limits of Cl. Current studies are being conducted to see if there are improved detection limits for any other elements on the periodic table with the use of other noble gases. The problem with Kr and Xe is that they are quite expensive.

About the Author

Dr.Badruddin Khan teaches Chemistry in the University of Kashmir, Srinagar, India.