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A nonmetallic gaseous element. Oxygen is the most abundant element on earth; it makes up 46.6% of the earth's crust and 20.95% of the earth's atmosphere where it exists primarily as a diatomic gas, O2. Oxygen was first recognized as an element by Joseph Priestly in 1774. It liquefies at -133C (at a pressure of 59 atmospheres). Liquid oxygen is used in medicine and diving as a breathing aid. It is also use for Acetylene and oxyhydrogen torches to weld and cut metals. Oxygen and oxidizing agents can corrode metals. Some metals, such as Aluminum, form an initial protective oxide layer that inhibits further reactions, while other metals, such as Iron, are continually reactive.

Synonyms and Related Terms

O; O2; dephlogisticated air; empyreal air; vital air; pure air; Zuurstof (Ned.); oxygène (Fr.); Sauerstoff (Deut.); ossigeno (It.); Oxigênio (Port.); oxi´geno (Esp.); Syre (Sven.)


  • Supports combustion. Electric sparks can cause an explosion in oxygen enriched air.
  • Airgas: SDS

Physical and Chemical Properties

Composition O (atomic no. 8)
CAS 7782-44-7
Melting Point -218.4 C
Molecular Weight atomic wt = 15.9994
Boiling Point -182.96 C

Resources and Citations

  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 566
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 7098
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Susan E. Schur, Conservation Terminology: A review of Past & Current Nomenclature of Materials, Technology and Conservation, Spring (p.34-39); Summer (p.35-38); Fall (p.25-36), 1985