The atom
Lithium losing electrons

Lithium has one electron in the outer energy level. It will give an electron away.

Notice how the lithium atom gives one electron away. The imbalance of protons and electrons now creates a charge of +1 on the atom.

Atoms with a charge are known as IONS. More precisely atoms with a positive charge are known as cations while atoms with a negative charge are known as anions. Lithium, above, forms a cation.