The name phosphorus is the Greek "bringing light" since white phosphorus will oxidise spontaneously in air and produce a glow. Phosphorus is less abundant than its neighbours in the periodic table sulphur and silicon, a factor explained by the uneven number of electrons in its outer shell. It has three allotropic forms: a black powder; a white-yellow, waxy solid; and a red-brown powder. Phosphorus compounds are noted for their stability owing to their forming double and triple covalent bonds. This is a property which leads to phosphorus compounds being potentially toxic, as when these chemicals react with various chemicals of the body, they create strong free radicals not easily processed by the liver, where they may accumulate.
The radiosotope 32P is routinely used as a tracer element in the laboratory. 33P is also used in circumstance where lower energy beta emissions are advantageous.