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Ionic Compound Formula from Charge Balance

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State

An ionic compound's formula uses the smallest whole-number ratio of cations to anions that makes the compound's total charge zero.

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Calcium's 2+ charge and chloride's 1− charge combine in a 1:2 ratio, giving the formula CaCl2.

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Balancing charge to zero sets the formula's subscripts — it does not describe how many ions physically touch in the crystal.