White phosphorus, yellow phosphorus or simply tetraphosphorus () exists as molecules of four phosphorus atoms in a tetrahedral structure, joined by six phosphorus—phosphorus single bonds. The tetrahedral arrangement results in ring strain and instability.  Although both are called "white phosphorus", in fact two different crystal allotropes are known, interchanging reversibly at 195.2 K.  The element's standard state is the body-centered cubic &alpha; form, which is actually metastable under standard conditions. The β form is believed to have a hexagonal crystal structure.  
Molten and gaseous white phosphorus also retains the tetrahedral molecules, until  when it starts decomposing to  molecules. The  molecule in the gas phase has a P-P bond length of r = 2.1994(3) Å as was determined by gas electron diffraction. The β form of white phosphorus contains three slightly different  molecules, i.e. 18 different P-P bond lengths &mdash; between 2.1768(5) and 2.1920(5) Å. The average P-P bond length is 2.183(5) Å.
White phosphorus is a translucent waxy solid that quickly yellows in light, and impure white phosphorus is for this reason called yellow phosphorus. It glows greenish in the dark (when exposed to oxygen) and is highly flammable and pyrophoric (self-igniting) upon contact with air. It is toxic, causing severe liver damage on ingestion and phossy jaw from chronic ingestion or inhalation. The odour of combustion of this form has a characteristic garlic smell, and samples are commonly coated with white "diphosphorus pentoxide", which consists of  tetrahedral with oxygen inserted between the phosphorus atoms and at their vertices. White phosphorus is only slightly soluble in water and can be stored under water. Indeed, white phosphorus is safe from self-igniting when it is submerged in water; due to this, unreacted white phosphorus can prove hazardous to beachcombers who may collect washed-up samples while unaware of their true nature.  is soluble in benzene, oils, carbon disulfide, and disulfur dichloride.