Hydrogen difluoride
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The hydrogendifluoride ion is the hydrogen-bonded anion [HF2]−. It can be considered as a molecule of HF that is hydrogen bonded to an F− ion: [F−H···F]−. There is a high degree of covalency in this particularly strong hydrogen bond, and both F−H distances are equal: each is 114 pm long1.
[edit] Salts
Some [HF2]− salts are stable and common, examples including KHF2 and [NH4][HF2].
[edit] Autodissociation of pure HF
The hydrogendifluoride ion also contributes to the unusually high acidity of neat hydrofluoric acid, which autodissociates in a manner similar to the self-ionization of water. This equilibrium can be denoted as
- HF ⇌ H+ + F−
However, both the H+ and F− ions are solvated by HF, so a more accurately descriptive equation is
- 3HF ⇌ [H2F]+ + [HF2]−
[edit] References
- Greenwood, N. N.; A. Earnshaw (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
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