What happens when sodium mixes with water?

This dramatic chemical reaction is a perfect illustration of pure elemental power. Sodium is an alkali metal, a family of elements known for being extremely reactive. It has one loosely held electron that it is desperate to give away. Water, H₂O, is a willing recipient. When they meet, the sodium atom violently rips a hydrogen atom off a water molecule, instantly forming flammable hydrogen gas (H₂) and sodium hydroxide (NaOH).

This process is incredibly exothermic, meaning it releases a tremendous amount of energy as heat. The heat is so intense that it immediately ignites the hydrogen gas that was just created. This rapid ignition of gas is what causes the bright yellow flame and the explosive bang. The unreacted sodium metal often melts into a silvery ball that skitters across the water's surface, propelled by the escaping gas like a tiny, fiery speedboat.

The entire event is over in seconds, leaving behind not plain water, but a corrosive solution of sodium hydroxide, also known as lye. This reactivity is why pure sodium is never found in nature and must be stored in oil to keep it from reacting with the humidity in the air.