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

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

• 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.

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

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

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

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.

• 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.