The empirical formula of magnesium oxide is MgO because it represents the simplest whole-number ratio of magnesium atoms to oxygen atoms in the compound. When magnesium burns in oxygen, it forms a white ionic compound where each magnesium atom loses two electrons (forming Mg²⁺) and each oxygen atom gains two electrons (forming O²⁻). This creates a 1:1 ratio of magnesium to oxygen atoms by count. The empirical formula shows only this simplest ratio, not the actual number of atoms in a particular molecule or crystal structure. In the case of magnesium oxide, the empirical formula MgO also happens to be the molecular formula because the compound forms an ionic solid lattice rather than discrete molecules. The 1:1 stoichiometry arises from the electron-transfer chemistry: magnesium in Group 2 of the periodic table naturally forms 2+ cations, while oxygen in Group 16 naturally forms 2− anions, so one atom of each is needed to balance the charges and achieve electrical neutrality. This is why we write MgO rather than Mg₂O₂ or any other multiple of the basic 1:1 ratio.