2.0 Boron

  p Block Elements

Important minerals of boron are:

• Borax – $Na_2B_4O_{7}.10H_2O$ or $Na_2[B_4O_{5}(OH)_4].8H_2O$
  

• Colemanite – $Ca_2B_6O_{11}.5H_2O$

• Boric acid – $H_3BO_3$

• Two isotropic forms of boron are: ${}_5{B^{10}}$ $(19\%)$ and ${}_5{B^{11}}$ $(81\%)$

Preparation:

• Two allotropic forms of boron are amorphous boron (dark brown) and crystalline boron.

• Reation with air ($O_2$ and $N_2$)

• Reaction with water

• Reaction with acids: With concentrated $H_2SO_4$ (oxidising acid) oxidises boron to boric acid while $HCl$ (a non-oxidising acid) has no action on boron.

• Reaction with alkalies

• Reaction with metals and non-metals

• Reducing nature: Boron is a powerful reducing agent as shown in reaction with $CO_2$, $SiO_2$ and $NO$.