Sodium is a soft, silvery metal that reacts dramatically with water, bursting into flames on contact. Pure sodium is so reactive that it must be stored in oil to keep it away from moisture in the air.

You encounter sodium every day, though never in its pure form. Table salt is sodium chloride, a compound where sodium atoms bond tightly with chlorine atoms. Your body needs sodium to work properly: it helps your nerves send signals, your muscles contract, and your cells maintain the right balance of water. When you sweat during exercise, you lose sodium, which is why sports drinks contain it.

In chemistry class, you might see a demonstration where a teacher drops a tiny piece of sodium into water. The metal skitters across the surface, fizzing and sparking, sometimes even popping or briefly flaring. This happens because sodium is incredibly eager to give up one of its electrons and form compounds with other elements.

On the periodic table, sodium has the symbol Na, from its Latin name natrium. Foods like pretzels, pickles, and canned soup often contain lots of sodium, which is why they taste especially salty.