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A sesquioxide is an oxide containing three atoms of oxygen with two atoms (or radicals) of another element. For example, aluminium oxide (Al2O3) is a sesquioxide. Many sesquioxides contain the metal in the +3 oxidation state and the oxide ion, e.g., Al2O3, La2O3. The alkali metal sesquioxides are exceptions and contain both peroxide, (O2−
) and superoxide, (O
) ions, e.g., Rb2O3 is formulated [(Rb+
].[1] Sesquioxides of iron and aluminium are found in soil.

Sesquioxidizing, meaning the creation of a sesquioxide, is the highest scoring word that would fit on a Scrabble board,[2] though it does not actually appear in any official Scrabble dictionary.[citation needed] The word first occurred in 1976 in Josepha Heifetz Byrne's Mrs. Byrne's Dictionary of Unusual, Obscure, and Preposterous Words (ISBN 0806504986), though the Oxford English Dictionary already listed sesquioxidized and sesquioxidation.[3] One could theoretically score 2044 points in a single move, when otherwise only words from the official Scrabble word list are used.[4]

List of sesquioxides[edit]

P2O3, existing as [[P4O6]]


  1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9. 
  2. ^ The Scrabble Omnibus, Gyles Brandreth, ISBN 0-00-218081-2
  3. ^ Keith W. Smith Total scrabble, page 67
  4. ^ Record for the Highest Scoring Scrabble Move at, accessed 2008-05-30