Rare gases

The noble gases occupy Group 8A of the periodic table. They react only with fluorine and chlorine, halogens from Group 7A.

The rare gases, a group of six elements—helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn)—are also known as the noble gases. These colorless, odorless, tasteless gases occur in the atmosphere in monoatomiciorm. Unlike hydrogen, nitrogen, and oxygen, they exist as single atoms, rather than diatomic molecules. They are remarkable for their lack of reactivity. The outer shells of their atoms have a full complement of electrons, so the atoms neither attract electrons from other atoms nor give up electrons to other atoms.

Their lack of reactivity lends itself to important industrial uses. All the rare gases except radon are used as light sources in incandescent and gas-discharge lamps, including electric light bulbs and fluorescent light fixtures. They are also used in making metals and alloys, in chemical processes, and in nuclear reactors, serving as a “blanket” for materials that would otherwise react violently with air or nitrogen.


Although rare on earth, this gas is one of the most common elements in the universe. All stars, including the sun, are composed of hydrogen and helium. Helium was discovered in the mineral clevite in 1895 by the Scottish chemist William Ramsay (1852-1916). It was named after the Greek helios, meaning sun, because it was first detected in the sun’s spectrum. Its atomic number is 2, and its atomic mass is 4.0026. Its melting point is -272.2° C, and its boiling point,-269.9° C.

Lighter than air, helium is used to fill balloons (below) and airships.

Helium is used as a coolant for rocket fuel and in a type of arc welding. Lighter than air, it is used to fill balloons and airships. A mixture of helium and oxygen makes breathing easier for people with asthma. A similar mixture is used for deep-sea diving, to help prevent nitrogen narcosis (the “bends”).

Neon to radon

Neon is used to fill lamps and luminous sign tubes. When an electric current is passed through it, the gas emits a reddish-orange glow. Neon was also discovered by Ramsay, with Morris Travers (1872-1961), in 1898 in impure argon from air. Its name derives from the Greek neos, meaning new. Its atomic number is 10, and its atomic mass is 20.179. Its melting point is -248.67° C, and its boiling point is -246.048° C.

Argon is mixed with nitrogen to fill electric light bulbs, where it keeps the filament from burning up. It is also used in arc welding, like helium. Argon was isolated from air in 1894 by Ramsay and Lord Rayleigh (1842-1919). Its name comes from the Greek argos, meaning inactive. Its atomic number is 18, and its atomic mass is 39.948. Its melting point is -189.2° C, and its boiling point, -185.7° C

Krypton, combined with argon, fills most fluorescent lamps. In luminous-sign tubes, it glows with a greenish-yellow light Krypton was discovered by Ramsay and Travers in 1898. It is named after the Greek kryptos, meaning hidden. Its atomic number is 36, and its atomic mass is 83.80. Its melting point is -156.6° C, and its boiling point, -152.3° C.

Xenon is used in the electric flash guns of cameras and in some high-power electric lamps. Xenon, from the Greek word for strange, was also discovered by Ramsay and Travers in 1898. Its atomic number is 54, and its atomic mass is 131.29. Its melting point is -111.9° C, and its boiling point,-107.1° C

Radon, a heavy radioactive gas, is produced by the radioactive decay of radium in soil and rocks. There are at least 28 isotopes—3 are natural, and the rest are produced artificially. Inhaled in sufficient quantities, radon can cause lung cancer. Radon was discovered by the German chemist Friedrich Dorn (1848-1916) in 1900. It was later isolated by Ramsay. It is formed by the radioactive decay of radium, after which it is named. It is itself radioactive. Its atomic number is 86, and the atomic mass of its most stable isotope is 222. Its melting point is -71° C, and its boiling point,-61.8° C.

A neon sign consists of a glass tube (A) containing neon gas at low pressure. Positive ions, striking an electrode, generate secondary electrons. A neutral neon atom (B) has 10 electrons. A secondary electron excites an outer electron (C), making it jump to a higher energy level. When the excited electron Jumps back, its excess energy is emitted as red light (D).