Phosphorus (P) is a highly reactive chemical element with atomic number 15. While there's quite a variety of phosphorus isotopes, the only stable one is ³¹P, with 15 protons and 16 neutrons.

A characteristic property of phosphorus is its ability to glow when exposed to air, and rougly translated phosphorus means light bearer in Greek.

Just like carbon, phosphorus exists in various different allotropes (different forms depending on how the atoms are bonded together), which include white phosphorus, red phosphorus and black phosphorus.

Despite its relatively long name, phosphorus is one of the few elements whose name can be spelled using element symbols: P - H - Os - P - Ho - Ru - S.