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Valency, SummaryThe valency, or combining capacity, of an element is measured by the number of atoms of hydrogen or its equivalent, which can combine with, or be displaced by, one atom of the element. Hydrogen valencies vary from 1 to 4. Oxygen is bivalent (H2O); elements in oxygen compounds can have valencies from 1 to 8. OsF8 is also known. The inactive gases, since they form no compounds, may be regarded as zero-valent.
Structural formulae are obtained by linking the atoms (or radicals) so as to satisfy all the valencies in pairs, e.g.,
 , or CH3-CH3.
Saturated molecules may combine to form molecular compounds; these may be assumed to be formed by residual valencies: KF...HF.
Unsaturated compounds contain latent valencies, represented by double or triple bonds, which can add on univalent atoms in pairs to form saturated compounds: CH2:CH2 + Cl2 = CH2Cl?CH2Cl.
The simple ideas of valency given in this chapter are considerably extended, and in some cases modified, in the sequel.Valency, Articles |
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