Gaining and losing electrons

Atoms become ions by gaining or losing electrons. And ions that have a positive charge are called cations. The progression goes like this: The Na⁺ ion is formed from the loss of one electron. Because it lost an electron, it has more protons than electrons, or more positive charges than negative charges, which means it’s now called the Na⁺ cation. Likewise, the Mg²⁺ cation is formed when the neutral magnesium atom loses two electrons.

Now consider the chlorine atom in sodium chloride. The neutral chlorine atom has acquired a negative charge by gaining an electron. Because it has unequal numbers of protons and electrons, it’s now an ion, represented like this: Cl^–. And because ions that have a negative charge are called anions, it’s now called the Cl^– anion.