• The ability of one chemical element to combine with another in specific proportions. It is expressed as the number of bonds that an atom of a given element forms when combined with other elements. Hydrogen is assigned a valence of one, so valence is the number of hydrogen atoms, or their equivalent, that an atom can combine with or replace when forming compounds. For example, in HCl, both chlorine and hydrogen have a valence of one, in H2O oxygen has a valence of two, while in SiO2 silicon has a valence of four. An element may have more than one valence.
  • The valence (1) of a molecule, ion, or radical.
  • synonym valency

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