Can someone explain why the ratio of magnesium ions to chloride ions in MgCl2 is 1 :2
Mg is in group IIA and has two electrons in its outside shell. Cl is in group VIIA and has seven electrons in its outside shell. Mg wants to lose two electrons; Cl wants to gain one electron. So one Mg atom gives its two electrons to each of two Cl atoms and the formula is MgCl2.