Oxygen can react with metals due to differences in electronegativity, particularly between iron and oxygen, which leads to the formation of ionic bonds. While oxygen is typically bonded covalently, its interaction with metals like iron results in the breaking of these bonds and the creation of ionic bonds. This reaction is facilitated in the presence of moisture, where a thin aqueous film allows molecular oxygen to dissolve and react with iron, ultimately leading to the oxidation of iron to Fe(OH)3. In contrast, copper does not undergo the same reaction effectively due to the formation of a passive film that protects it from oxidation.