Question

What is the chemical formula for an ionic compound of potassium and oxygen?

Answer 1

Potassium oxyde, `K_2O`.

Explanation:

The last level of the electronic structure of oxygen is `2s^2 2p^4`. That means that there are two electrons in the `2s` orbital, two other electrons (paired) in one of the `2p` orbitals and the remaining two (unpaired) electrons placed one in each of the remaining `2p` orbitals.

This means that oxygen has two semi-occupied orbitals and, following the octet rule, will try to capture two more electrons to complete its structure and acquire that of a noble gas. That is, when it acts to form ionic bonds, oxygen acquires structure `2s^2 2p^6` in its last level, forming the ion oxygen (2-): `O^{2-}`.

On the other hand, potassium is an alkali metal whose last level occupied is `4s^1`. That means that it will have a lot of tendency to lose that solitary electron and thus to form ionic compounds in which it takes the form of cation `K^+`.

Therefore, the binding of oxygen and potassium will give rise to an oxide of ionic character and `K_2O` stoichiometric formula.