Class 12 Chemistry P Block Elements Phosphorous


It exists as P4 with tetrahedral geometry as shown below:



It has three forms:

  • White P
  • Black P
  • Red P


White phosphorous

  • It has a normal tetrahedral structure. They are soft waxy solids.
  • They can be cut with knife.
  • They are poisonous.
  • They are chemiluminescent.
  • It is most reactive form of phosphorous.
  • It undergoes disproportionate reaction as shown :
  • P4     +           NaOH --->            PH3    +           NaH2PO2
  • Phosphorous  Sodiumhydroxide  Phosphine  Sodiumhypo Phosphite
  • In this oxidation sate of phosphorous changer from 0 to +1 and -3.


Black phosphorous

It exists in two forms:

Alpha phosphorous

Beta phosphorous

Alpha phosphorous: is formed by heating red phosphorous at 803 K

Beta phosphorous: is formed by heating white phosphorous at 473K

It has most stable due to three dimensional structure as shown:


Alpha phosphorous


Red phosphorous

  • It is obtained by heating white phosphorous at 573 K in inert atmosphere.
  • It has polymeric structure as shown:


                                         Red phosphorous

  • It is crystalline solid.
  • It shines grey.
  • It is non poisonous.
  • It is more stable.
  • It is also chemiluminescent.
  • Stability of different forms of phosphorous:

White P< red P <black P

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