How to calculate the covalency of a compound

[AlCl(H2O)5]?2

Dear student,

Valency is the combining capacity of an atom. It is equal to the number of electrons the atom loses, or gains or shares when it combines with one or more atoms.

Depending on whether the atom loses, gains or shares electrons, the valency may be positive or negative or neutral respectively.

Example: Valency of sodium is + 1, because it can lose one electron. It is represented as Na⁺. Valency of oxygen may be - 2 if it accepts 2 electrons i.e., O^2-.

If two or more atoms combine by sharing electrons i.e., not losing or gaining electrons, then the valency numbers are neither positive nor negative. In the case of carbon dioxide, carbon and oxygen atoms, do not, lose or gain electrons, and their valencies are 4 and 2 respectively.

Certain atoms exhibit different kinds of valencies. This is because such elements can loose more than one electron from their outer most shell depending on the available conditions. When such atoms exhibit variable valency, the name of the atom with the lower valency ends as -ous, and the one with the higher valency, ends as -ic.

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All the best.

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Askiitians Expert

Sagar Singh

B.Tech, IIT Delhi

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