Phosphorus,White phosphorus,red phosphorus and black phosphorus

Phosphorus and white phosphorus structure


Phosphorus is the second member of group VA. It’s name phosphorus is a greek word which means light bearing. Phosphorus is not found in free state. The important minerals are:

  • Phosphate rock or phosphate, Ca3(PO4)2.
  • Fluorapatite Ca5F(PO4)3

It is found in seeds,yolk of eggs, Brain, nerves and bone marrows. The bone ash contain 80% calcium phosphate.

Allotropes of phos-phorus:

Phos-phorus exist in six allotropic form but we will explain only three forms white, red and black phos-phorus.

1-White Phosphorus:

White Phosphorus is very reactive, Wxy, volatile, Poisonous. It is soluble in benzoic and carbon disulphide. It exist in form of tetratomic molecule (P4). The structure of white phosphorus is tetrahedral.It’s Boling point is 280 °C .

P4    →    2P2

white phosphorus structure

A Tetrahedral molecule of P4 is shown in figure.

2- Red Phosphorus:

When white phos-phorus is heat at 2500c in vacuum in presence of iodine or sulfur as catalyst, then red phos-phorus is produce. It is less reactive and non-poisonous. It is insoluble in carbon disulphide. The structure of Red Phos-phorus is show bellow:

red phosphorus structure

When tetratomic molecule(P4) of white phos-phorus combine, they give macromolecule of red phosphorus.

3- Black Phosphorus:

It is third modification (form) of phos-phorus. It is the most stable form, When red phos-phorus is heat at high temperature and pressure, it changes to black phos-phorus.

Halides of Phos-phorus:

We explain preparation and properties of phos-phorus trichloride and phos-phorus Pentachloride.

Phos-phorus Trichloride (PCl3):


  1. Reaction of phos-phorus with thionyl chloride gives phos-phorus trichloride.

2P+ 4SOCl2 → 2PCl3+2SO2+S2Cl2

2) Reaction of white phos-phorus with chlorine gives phos-phorus trichloride.

2P+3Cl2 → 2PCl3

In this method, white phos-phorus is melted in a retort in an inert atmosphere of CO2. Then dried Cl2 is passed. The vaporus of PCl3 collect in a flask kept in an ice bath.

Physical Properties of PCl3:

  1. PCl3 is a colourless fuming liquid.
  2. It’s boiling point is 76c and freezing point is -112 °C .

Phos-phorus pentachloride PCl5:


1- PCl5 is prepare by passing dry chlorine through Pcl3.

PCl3 + Cl2  → PCl5

2-PCl5 is prepare by passing dry Cl2 through well cooled solution of phos-phorus in carbon disulphide.

2P+5Cl2 → 2PCl5

Physical properties:
  • PCl5 is yellowish white crystalline Solid.
  • It has irritating smell.
  • It sublimes at 100 c.
  • Pcl5 Gives white fumes in moist air.

Also read;

Preparation of Sodium

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About the Author: Waleed Ahmed

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