Sodium has one valence electron, which makes it very reactive with halogens and other nonmetals. Sodium is an alkali metal that is never found in its pure form in nature.
Sodium is a highly electropositive atom, which means that it does not hold onto its single electron very tightly. Like most metals, sodium is an electron donor. When sodium meets up with an electronegative atom, such as a halogen like chlorine, it readily gives up its one valence electron to the electronegative atom. The sodium atom becomes an ion with a positive charge; the electronegative atom becomes a negative ion. The positive sodium ion and the negative ion attract each other in an ionic bond.