Phosphorus and its compounds
It is the second member of group 15 (VA) of the Periodic table. Due to larger size of P, it cannot form stable P- P bonds with other phosphorous atoms where as nitrogen can form P – P bonds.
(1) Occurrence : Phosphorous occurs mainly in the form of phosphate minerals in the crust of earth. Some of these are:
(i) Phosphorite Ca3 (PO4)2,
(ii) Fluorapatite Ca5(PO4)3 F,
(iii) Chlorapatite 3Ca3 (PO4)2. CaCl2,
(iv) Hydroxyapatite; Ca5 (PO4)3 OH.
Phosphates are essential constituents of plants and animals. It is mainly present in bones, which contains about 58% calcium phosphate.
(2) Isolation : Elemental phosphorus is isolated by heating the phosphorite rock with coke and sand in an electric furnace at about 1770K,
P4P10 + 10C → P4 + 10CO
(3) Allotropic forms of phosphorus : Phosphorus exists in three main allotropic forms,
(i) White phosphorus, (ii) Red phosphorus, (iii) Black phosphorus
Some physical properties of three forms of phosphorus
| Properties | White phosphorus | Red phosphorus | Black phosphorus |
| Colour | White but turns yellow on exposure | Dark red | Black |
| State | Waxy solid | Brittle powder | Crystalline |
| Density | 1.84g cm–3 | 2.1 g cm–3 | 2.69 g cm–3 |
| Ignition temperature | 307 K | 533 K | 673 K |
| Stability | Less stable at ordinary temperature | More stable at ordinary temperature | Most stable |
| Chemical reactivity | Very reactive | Less reactive | Least reactive |
