The ionic formula for Lithium Oxide is ##Li_2O##.

Lithium is an Alkali Metal in the first column of . This means that lithium has 1 valence electron it readily gives away in order to seek the stability of the octet. This makes lithium a ##Li^(+1)## cation.?

Oxygen is in the 16th column or ##p^4## group. Oxygen has 6 . It needs two electrons to make it stable at 8 electrons in its valence shells. This makes oxygen a ##O^(-2)## anion.

Ionic bonds form when the charges between the metal cation and non-metal anion are equal and opposite. This means that two ##Li^(+2)## cations will balance with one ##O^(-2)## anions.

This makes the formula for lithium oxide ##Li_2O##

I hope this is helpful. SMARTERTEACHER