11th Chemistry NCERT notes

Anomalous Properties of Boron

Boron shows anomalous behavior with the other members of the group, due to the following reasons:

  • Smallest size in the group
  • High ionization energy
  • Highest electronegativity in the group.
  • Absence of vacant d-orbital

Some Important Compounds of Boron (B)


  • Borax is a white crystalline solid.
  • It contains tetranuclear units. [B4O5(OH)4]2-
  • It formula is Borax formula
  • Borax dissolves in water to give an alkaline solution

Borax reaction with water

  • Borax is used as a water softener and cleaning agent.

Orthoboric acid (H3BO3) or B(OH)3

Boric acid can be prepared by the acidification of aqueous solution of borax.

Orthoboric acid (H3BO¬3) or B(OH)3

It can also be prepared by the hydrolysis of boron compounds.

Orthoboric acid (H3BO¬3) or B(OH)3

Physical properties of Boric acid

  • It is a white crystalline solid.
  • It is soft soapy in touch.
  • It is sparingly soluble in cold water but fairly soluble in hot water.

Uses of Boric acid

  • In the manufacture of heat resistant borosilicate glazes.
  • As a preservative for milk and food stuffs.
  • In the manufacture of enamels and glazes in pottery.

Structure of Boric Acid

Structure of Boric Acid

Diborane (B2H6)

  • The series of compounds of boron with hydrogen is known as boranes.
  • Diborane is prepared by the reduction of boron trifluoride with LiAlH4 in diethyl ether.


  • Laboratory method of preparation. In laboratory diborane is prepared by the oxidation of sodium borohydride with iodine.


  • Industrial method of preparation. On industrial scale, diborane is prepared by reduction of BF3 with sodium hydride.


Structure of Diborane

Structure of Diborane

Physical Properties of Diborane

  1. Diborane is a colourless, highly toxic gas with a b.p. of 180 K.
  2. Diborane catches fire spontaneously upon exposure to air.
  3. Higher boranes are spontaneously flammable in air.

Chemical Properties

  • Boranes are readily hydrolyzed by water to form boric acid.

Boranes are readily hydrolyzed by water to form boric acid

  • It burns in oxygen evolving an enormous amount of heat.

It burns in oxygen evolving an enormous amount of heat.

  • Reaction with Lewis base: Diborane on treatment with lewis bases undergo cleavage reactions to form borane which then reacts with Lewis bases to form adducts.

Reaction with Lewis base



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