Sodium is a solid at standard temperature and pressure. It is the sixth most common element in the Earth's crust, but it is highly reactive and is never found as a pure element in nature.
Sodium is a soft, bright, silvery metal that oxidizes quickly when exposed to air. Its reactive nature allows it to form many familiar chemical compounds, including sodium chloride, sodium hydroxide and sodium carbonate. It is an essential nutrient in humans, due to its role in regulating blood volume and pressure, osmotic equilibrium and pH. Elemental sodium requires careful handling because it reacts exothermically with water, sometimes with explosive results, producing flammable hydrogen gas and caustic hydrogen peroxide.