## Chemistry: The Central Science (13th Edition)

$K_2Cr_2O_7$
This is an ionic compound. The cation is potassium, which as a cation always has a charge of 1+ because it has one valence electron. The anion is dichromate, $Cr_2O_7$, which has a charge of 2-. To have an electrically neutral atom, there needs to be two atoms of potassium for every one molecule of dichromate.