valency

valency (vāˑ·len·sē),

n the number of chemical bonds that an atom of a particular element can form, used as a measure of the chemical reactivity of that element.

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valency, valence

1. the numerical measure of the capacity to combine; in chemistry, an expression of the number of atoms of hydrogen (or its equivalent) that one atom of a chemical element can hold in combination, if negative, or displace in a reaction, if positive.

2. in immunology, an expression of the number of antigenic determinants with which one molecule of a given antibody can combine.