Question

What is the chemical formula for the compound formed between chromium(III) and the iodate ion?

Answer 1

Chromium(III) has 3 positive charges (which is indicated by the roman numerals in parentheses).

The iodate ion, being in group 7, tends to gain an electron (to complete it's octet) and becomes a negative ion with a charge of -1.

The formula needs to be an electrically neutral/balanced compound, so we need as many negative charges as positive charges.

1 \(Cr^{3+}\) has 3+
1 \(I^-\) has 1-

we need 3 \(I^-\) to make 3- and balance the 3+ from \(Cr^{3+}\).

the formula is \(\sf CrI_3\)