A strange and dangerous glow – White phosphorus

What does it look like?

White phosphorus consists of tetrahedral P₄ molecules in which each phosphorus atom is bonded to the three other atoms of the tetrahedron. The P₄ molecule exists in the solid, liquid or gas phase up to temperatures of 800 °C, and in the solid phase exists in a low temperature b-phase or high temperature a-phase that differ in the relative orientation of the P₄ tetrahedra. White phosphorus is soft and waxy, insoluble in water and glows in the dark.

The strange group of phosphorus

Where did the structure come from?

Discovered around 1669 by the alchemist Hennig Brand during his search for the elusive "philosopher’s stone" and whilst heating the "golden stream" (urine) with charcoal at very high temperatures, Brand obtained glowing fumes and an unusual white solid that burned and glowed with an eerie pale-green light.

The structure of white phosphorus was first reported by G. Natta and L. Passerini in 1930.

What is it?

White phosphorus is the most important of the four allotropes of phosphorus (the others being red, violet and black). Like the allotropes of carbon (such as Graphite, buckyballs and diamond), these materials differ in their crystal structure but are made up of the same element. The chemiluminescent glow of white phosphorus is due to the slow oxidation of its vapours with air. It is highly flammable and pyrophoric (self-igniting). For this reason, white phosphorus was once used in parlour tricks, matches, fireworks, and by military forces in incendiary bombs. Workers who produced matches and inhaled white phosphorus vapours often developed "Phossy jaw", or dissolving of the jaw bone, while contact with the hot liquid causes burning deep into tissue. The use of white phosphorus was banned in matches in 1906, and in incendiary weapons against civilians in 1980.

Today, around 850 000 tonnes of white phosphorus are produced for peaceful uses, namely as a raw material for the production of phosphoric acid, pharmaceuticals and fertilisers.

Tags: chemiluminescence   phosphorus   pyrophoric   tetrahedra   elements