Phosphorous and Compounds




a) It shows the property of catenation to maximum extent due to most stable P – P bond.

b) It has many allotropes, the important ones are:
i) White phosphorus
ii) Red phosphorus
iii) Black phosphorus


White phosphorus


1.     Discrete tetrahedral P4 molecules

2.     Very reactive

3.     Glows in dark

4.     Translucent waxy solid

5.     Soluble in but insoluble in water

6.     It has low ignition temperature, therefore, kept under water


Red phosphorus

1.     Polymeric structure consisting of chains of P4 units linked together

2.     Less reactive than white phosphorus

3.     Does not glow in dark

4.     Has an iron grey lustre

5.     Insoluble in water as well as


Black phosphorus

1.     Exists in two forms –  black phosphorus and  black phosphorus

2.     Very less reactive

3.     Has an opaque monoclinic or rhombohedral crystals




1.     It is highly poisonous, colourless gas and has a smell of rotten fish.

2.     Preparation


Phosphorus Halides  

Phosphorus Trichloride  

i) It is a colourless oily liquid.

ii) Preparation

iii) With water,
It gets hydrolysed in the presence of moisture.

iv) Pyramidal shape, sp3 hybridisation

v) With acetic acid

vi). With alcohol


Phosphorus Pentachloride       

1.     Yellowish white powder.

2.     Trigonalbipyramidal shape, sp3dhybridisation .

3.     Preparation


5.     With water


7.     With acetic acid


9.     With metals


Oxoacids of Phosphorus 


Hypo Phosphorous Acid (H3PO2) or Phosphinic Acid

It is set up by the oxidation of phosphine by iodine within the sight of figured amount of water. It is a monobasic acid.

PH+ 2I2 + 2H2O -----------> H3PO2 + 4 HI


Fig. 1: Hypo Phosphorous Acid

Phosphorous Acid (H3PO3) or Phosphonic Acid

It is set up by hydrolysis of phosphorous trioxide (P4O6). Phosphorous acid is dibasic in nature.

P4O6 + 6H2O ----------> 4H3PO3


Fig. 2: Phosphorous Acid

Hypophosphoric Acid (H4P2O6)

It is set up by controlled oxidation of red phosphorus with sodium chlorite arrangement when disodium salt of the hypophosphoric acid is obtained it is passed through cation exchanger to yield hypophosphoric acid. Hypophosphoric acid is tetrabasic in nature.

2P + 2NaClO2 + 2H2O ---------> Na2H2P2O6 + 2HCl
Na2H2P2O6 + 2H -----resin-----> H4P2O6 + 2Na – resin


Fig. 3: Hypophosphoric Acid

Orthophosphoric Acid (H3PO4)

It is set up by treating P4O10 with bubbled water. It is a tribasic acid.

P4O10 + 6H2O ----------> 4H3PO4


Fig. 4: Orthophosphoric Acid

Pyrophosphoric Acid (H4P2O7)

It is set up by heating orthophosphonic acid at about 250oC. It is a tetrabasic acid.

2H3PO4 ---------> H4P2O7 + H2O


Fig. 5: Pyrophosphoric Acid

Meta Phosphoric (HPO3)n

It is formed by warming orthophosphoric acid to around 850 K. Metaphosphoric acid does not exist as monomer. It exists as cyclic trimer, cyclic tetramer or polymer.

H3PO---------> HPO3 + H2O


Fig. 6: Metaphosphoric Acid

The structures of oxoacids of phosphorus are efficiently given ahead:




Fig. 7: Structure of oxoacids of phosphorus with their oxidation states and basic nature