corrosion
The driving force to combine with nonmetals to create ionic compounds varies quite a bit between different metals. Some pure metals, like cesium and potassium, are so eager to react that they must be stored under oil to avoid an immediate reaction with the oxygen present in air. Others, like platinum and gold, are stable enough that they can be found in nature as pure metals rather than as the cationic portion of an ionic compound. Gradual degradation of a material due to its exposure to the environment is known as corrosion . Metals like gold and platinum are unusually resistant to corrosion, which makes them especially valuable for both structural and decorative purposes.