NEET Chemistry Notes p-Block Elements – Group 13 Elements: Boron Family

NEET Chemistry Notes p-Block Elements – Group 13 Elements: Boron Family

Group 13 Elements: Boron Family

Group 13 Elements: Boron Family

Boron (B), aluminium (Al), gallium (Ga), indium (In) and thallium (Tl) are the members of group 13. Boron is non-metal while rest of the members are metals.

Important Properties

•  General Configuration ns¹, np¹

• Oxidation State +3,+1

Stability of +3 oxidation state decreases down the group and that of 1 oxidation state increases down the group due to inerteffect. Fourth period and onwards effective nuclear charge increases due to poor shielding effect, therefore the radius of gallium (135 pm) is less than that of aluminium (143 pm) and down the group, inert pair effect increases.

• Hydrides

Boron hydrides exist in dimeric or polymeric form. The simplest boron hydride is diborane,B₂H₆ Aluminium forms only one colourless, solid polymeric hydride (AlH₃)_n, , known as alane. B, Al and Ga form complex anionic hydrides, e.g. NaBH₄, LiAlH₄ and LiGaH ₄.
All are strong reducing agents
LiAlH₄ >NaBH₄ (reducing power)

• Halides

Halides have incomplete octet, therefore, have a high tendency to accept electrons and behave as Lewis acid.
BI₃ > BBr₃ > BC1₃ > BF₃ (acidic character)
Due to back bonding and resonance, the B-F bond of BF₃ gets a bond order of 1.33.

• Oxides

Down the group, their basic character increases, e.g. B₂0₃ is weakly acidic,  A1₂0₃ is amphoteric and other oxides are basic in nature.

Preparation, Properties and Uses of Boron

Occurrence

The important minerals of boron are borax (Na₂B₄0₇ 10H₂O), orthoboric acid (H₃B0₃) and kernite (Na₂B₄0₇ 4H₂ O)

Preparation

Now a days boron is obtained by electrolysis of a fused mixture containing boric anhydride, magnesium oxide and magnesium fluoride at 1100°C.

Crystalline boron is obtained by the reduction of B203 with aluminium powder.

Amorphous boron of low purity is called Moissan boron. It is black in colour.

Physical Properties

Boron exists in two allotropic forms, i.e. amorphous and crystalline. Crystalline boron is chemically inert while amorphous boron is chemically active. It is a bad conductor of heat and electricity.

Chemical Properties

• Amorphous boron on heating with air at 700°C forms a mixture of oxide and nitride.
  
• Boron is attacked by oxidising acids like conc H₂S0₄ and HN0₃.
• 
  It dissolves in fused alkalies and liberates hydrogen.
  It reacts with strong electropositive metals at high temperature and forms borides such as Mg₃B₂.
• It is a powerful reducing agent.
  

Uses

It is used as control rods in atomic reactors and as a deoxidiser.

Preparation, Properties. and Uses of Aluminium

Occurrence

The important ores of aluminium are bauxite A10_x(OH)₃__2x (where 0<x<l) and kaolinite [Al₂(OH)₄Si₂O_s]

Preparation

Bauxite contains Si0₂, iron oxides and titanium oxide (Ti0₂) as impurities. Leaching of bauxite ore is carried out with cone. NaOH solution.

Hall-Heroult Process

Aluminium is obtained by the electrolysis of A1₂0₃ mixed with Na₃AlF₆ or CaF₂. Overall reaction is as follows

Physical Properties

It is bluish white lustrous metal and loses its lustre due to the formation of protective oxide film A1₂0₃ . It is light, malleable, ductile, good conductor of electricity and heat.

Chemical Properties

With Alkalies Al readily dissolves in alkalies evolving H₂ and forming the corresponding aluminates.

With Acids The metal dissolves in dil. HCl and dil. H₂S0₄ solutions evolving H₂. Conc. HN0₃  has no reaction, the metal rendered passive due to surface oxidation.

Uses

It is used for making house hold utensils, frames, bodies of aircraft automobiles etc. It is used in making paints, as a mordant in dyeing and calico printing. Ammonal (mixture of A1 powder and ammonium nitrate) is used as explosive. Magnalium, duralumin and alnico are important alloys of aluminium.

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