Here's why:

* Lithium (Li) is in group 1 of the periodic table, meaning it has a +1 charge when it forms an ion.

* Oxygen (O) is in group 16 of the periodic table, meaning it has a -2 charge when it forms an ion.

To create a neutral compound, you need two lithium ions (+1 each) to balance the charge of one oxygen ion (-2). This gives you the formula Li₂O.