Occurrence, Isolation, and Properties of Phosphorus

Phosphorus occurs mainly in the form of phosphate minerals. The principal source of phosphorus is phosphate rock, which contains phosphate principally as Ca3(P04)2. The element is produced commercially by reduction of calcium phosphate with carbon in the presence of Si02i 

The phosphorus produced in this fashion is the aUotrope known as white phosphorus. This form distills from the reaction mixture as the reaction proceeds. 

Phosphorus exists in several aUotropic forms. White phosphorus consists of P4 tetrahedra ( FIGURE 22.27). The bond angles in this molecule, 60°, are unusually small, so there is much strain in the bonding, which is consistent with the high reactivity of white phosphorus. This aUotrope bursts spontaneously into flames if exposed to air. When heated in the absence of air to about 400 °C, white phosphorus is converted to a more stable aUotrope known as red phosphorus, which does not ignite on contact with air. Red phosphorus is also considerably less poisonous than the white form. We wUl denote elemental phosphorus as simply P(s). 

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