Question

How can you represent the composition of an ionic compound?

Answer 1

By the ratio of cations to anions in the empirical formulae.

Explanation:

Ionic compounds are non-molecular species, and their formulae are represented by their empirical formulae, simple, whole number ratios.

Of course, ionic species are electrically neutral (most matter is of course electrically neutral). So when the alkali metals form an ionic compound with the halogen species, because the alkali metals readily form a `M^+` ion, they draft `X^-` halide ions to form the salt `M^+X^-`. Chalcogens, oxygen, and sulfur, etc. form dianionic ions, `O^(2-), S^(2-),`. To form neutral salts with the alkali metals, 2 cations must be drafted: `Na_2O, Na_2S`.

For the following cations, `Na^+`, `Ca^(2+)`, and `Al^(3+)`, can you formulate the ionic compounds formed with the `I^-`, `NO_3^-`, and `PO_4^(3-)` anions? Remember that electrical neutrality is the key.