10.1.1—Reactions of the elements with oxygen

Group 2 metals form oxides when heated in oxygen: 2M + O₂ → 2MO. The products contain M²⁺ and O²⁻ ions in an ionic lattice.

Reactivity generally increases down the group because the outer electrons are farther from the nucleus and more shielded, so they are easier to remove.

Magnesium burns in oxygen to form MgO. Barium reacts more readily than magnesium under comparable conditions because its outer electrons are less strongly held.

A more reactive metal does not necessarily produce a different oxidation state here. Group 2 metals commonly form +2 ions; the trend is about ease of reaction.