Final answer:
Magnesium reacts with oxygen to form magnesium oxide (MgO) because it is oxidized; it loses electrons to oxygen, which gains them. This chemical change results in the conversion of shiny magnesium to a white powder while adhering to the conservation of mass, with no change in total mass before and after the reaction.
Step-by-step explanation:
Magnesium (Mg) does not remain in its elemental form when it reacts with steam because it undergoes a chemical change to form magnesium oxide (MgO). The process of this transformation involves the reaction of magnesium with oxygen, where magnesium atoms are oxidized – they lose electrons – and oxygen atoms gain those electrons. The combination of magnesium and oxygen, following the principle of the conservation of mass, results in the same total mass before and after the reaction, but the substances have formed a new compound: magnesium oxide.
When magnesium burns in air, a reaction is observed, represented by the chemical equation: 2Mg (s) + O₂(g) → 2MgO (s). The magnesium reacts vigorously, releasing a bright white flame and heat, and the metallic element is converted into a crumbly white powder, which is magnesium oxide. This occurs because oxygen is a highly electronegative element, and magnesium has a strong tendency to lose electrons and form a stable oxide compound.