What is the chemical formula for chromium iodide?

The formula for chromium(II) iodide is CrI2, and the formula for chromium(III) iodide is CrI3. As denoted by the Roman numerals in the parentheses, chromium(II) carries a charge of +2, while chromium(III) carries a charge of +3.

The number of iodine atoms differs depending on the chromium ion because the charges in the equation must balance out. Iodine carries a charge of -1, so chromium(II) requires two iodine atoms to balance out its charge. Chromium(III) requires three iodine atoms to neutralize its +3 charge. To determine the formula for chromium iodide, the charge of the chromium ion must be known.