Final answer:
The ionic compound that forms between magnesium (Mg) and oxygen (O) is MgO, magnesium oxide, due to the transfer of two electrons from magnesium to oxygen forming Mg2+ and O2- ions.
Step-by-step explanation:
The ionic compound that forms between magnesium (Mg) and oxygen (O) has the formula MgO. This is because magnesium, which is in the second group of the periodic table, has two valence electrons and tends to lose them to achieve the electron configuration of the nearest noble gas, neon, forming a Mg2+ cation. Oxygen, on the other hand, has six valence electrons and needs two more to complete its octet, leading to the formation of an O2- anion. The compound is held together by the electrostatic attraction between the oppositely charged ions, hence one magnesium ion bonds with one oxygen ion to form MgO, magnesium oxide. The balanced chemical equation for this reaction is 2Mg + O2 → 2MgO, indicating that two magnesium atoms react with one oxygen molecule (which consists of two oxygen atoms) to produce two formula units of magnesium oxide.