# How do you name MgCl_2?

Magnesium is in group II and will always form a 2+ ion when reacting. Equally, chorine is I group VII and will tend to gain one electron from a metal to form a 1- ion. $M g C {l}_{\text{2}}$ is therefore the only possible formula for magnesium chloride.
Compare this to iron chloride. Iron can form a 2+ or 3+ ion, therefore you must make a difference in naming $F e C {l}_{2} =$ iron(II) chloride and $F e C {l}_{3} =$ iron(III) chloride.