Chemical Element: argon

(Greek: argus, neutral, inactive, idle, inert; gas)

Chemical-Element Information

Symbol: Ar
Atomic number: 18
Year discovered: 1894

Discovered by: Sir William Ramsay (1852-1916), a British chemist; and John William Strutt, Lord Rayleigh (1842-1919), a British physicist.

  • Rayleigh was trying to measure the atomic weight of nitrogen when he encountered an unexplainable result.
  • Whereas oxygen always had the same atomic weight no matter how it was prepared, nitrogen did not.
  • Nitrogen prepared from the atmosphere consistently showed a slightly higher atomic weight than nitrogen prepared from a variety of nitrogen-containing compounds.
  • Rayleigh could not find a suitable explanation for this and so he wrote a letter to the journal Nature, asking for suggestions.
  • British chemist William Ramsay accepted the challenge.
  • Ramsay repeated an experiment made by British chemist Henry Cavendish (back in 1766) who had tried to combine the nitrogen of air with oxygen and had found that a small bubble of gas remained behind, which would simply not combine with oxygen.
  • Cavendish apparently thought there might be some small quantity of gas in the atmosphere that was more dense than nitrogen, and more inert, too, but he did not pursue the matter.
  • Ramsay had access to spectroscopic techniques that Cavendish did not have.
  • He heated the bubble of gas, studied the spectral lines it emitted, and found them to be in positions that did not fit any known element.
  • It seemed obvious that there was an unknown gaseous element, that made up about one percent of the atmosphere.
  • It was completely inert and would not react with any substance; and it was also much more dense than nitrogen.
  • The presence of this new gas as an impurity in the nitrogen obtained from air gave it an abnormally high atomic weight, whereas nitrogen obtained from chemicals without any mixture of this impurity gave the true atomic weight.
  • The discovery was announced on August 13, 1894, and the new gas was named “argon”, from the Greek word for “inert”.
  • As a result, Rayleigh received the Nobel Prize in physics and Ramsay the Nobel Prize in chemistry in 1904.
  • It was isolated by examination of the residue obtained by removing nitrogen, oxygen, carbon dioxide, and water from clean air.
  • In fact, air contains less than one percent argon.
  • It was recognized by the characteristic lines in the red end of the spectrum.
  • Argon was the first of the noble gases to be isolated from a terrestrial source.
  • Helium was detected in the sun in 1868.

Name in other languages:

French: argon

German: Argon

Italian: argo

Spanish: argón

Information about other elements may be seen at this Chemical Elements List.

A special unit about words that include chemo-, chem- may be seen here.