Atomic Symbol: Ar

Atomic Weight: 39.948

Electron Configuration: 1s²2s²2p⁶3s²3p⁶

^{Boiling Point in Kelvin: 87.29}

^{Atomic Radius in nM: 0.174}

^{1st Ionization Energy in kJ/mole: 1520.4}

HISTORY

            Argon is the first noble gas to be discovered. Although its presence in air was suspected by Cavendish in 1785, it was found in 1894 by chemist William Ramsay. Ramsay was working under Lord Rayleigh, a professor of physics at the University of Cambridge in England, who was studying the density of nitrogen gas. Through experiments, Lord Rayleigh found that nitrogen separated from ammonia (NH₃) had a density of 0.5% less than that of nitrogen found in the air. He didn’t know why, so Ramsay decided to investigate.

            Ramsay removed the oxygen and nitrogen from a quantity of liquid air through fractional distillation. He found that there was a small residue of gas left. He put this residue in a glass tube and electrically excited it. When he studied the excited gas with a spectroscope, Ramsay discovered a new pattern of lines. Oddly, there seemed to be no place in the Periodic Table for a new gaseous element.

            In 1894 Ramsay had the idea for a new column of elements. He thought that this gas was the first member. Ramsay named this new element “argon,” for the Greek argos, meaning “lazy,” or “inactive.” Ramsay thought it was lazy because it seemed to have no chemical properties.

Where to Find Argon

            Argon is a colorless, odorless, tasteless gas that is found in the air. It exists free in nature and naturally occurs in three isotopes. Twelve other radioactive isotopes of argon are known to exist. Dry air contains less than 1% (about 0.94%) argon. This means that one cubic foot of air contains sixteen cubic inches of argon. Even though this may seem like a small percentage, argon is more abundant in the atmosphere than CO₂. It is the third most abundant gas in the atmosphere. The quantity has increased since the Earth was formed because radioactive potassium turns into argon as it decays.

CHEMICAL PROPERTIES AND SOLUBILITY

             Argon does not naturally form chemical compounds. Because it is a noble gas, all of its orbitals are full. There is no energy advantage in gaining an electron in a new shell, which would require 1.0 eV. Argon has a negative electron affinity and is about two and one half times as soluble in water as nitrogen, having about the same solubility as oxygen.

            Argon is used in welding processes because it provides an inert atmosphere in which metals will not oxidize, or burn. It is used as a protective atmosphere for the production of titanium and other reactive elements and for growing silicon and germanium crystals. It is also used in phototubes, glow tubes, neon signs, Geiger counters, and incandescent light bulbs. Argon is useful for black lights and UV lamps since excitation of the gas produces a large amount of ultraviolet radiation.