Explain how an ionic bond forms when magnesium atoms react with oxygen atoms.

If you look at the periodic table, magnesium (Mg) is in group 2, meaning it has 2 electrons on it's outer shell.

Oxygen (O) is in group 6, meaning it has 6 electrons in its outer shell.

To form an ionic bonds, both elements need to have full outer shells / 8 electrons in their outer shell.

Oxygen only needs 2 electrons to become an ion, and magnesium is able to give 2 away, so oxygen takes 2 from magnesium to form an ionic bond.