Short Answer TypeExplain the following:
(i) Boron has high melting and boiling points.
(ii) Aluminium is a good reducing agent.Â
Long Answer TypeDiscuss the characteristics of Group-13 elements in terms of metallic character and their tendency to exhibit inert pair effect.Â
Short Answer TypeBoron chloride exists a monomer while in the same group anhydrous, AlCl3 exists as a dimer?
White fumes appear around the bottle of anhydrous aluminium chloride.
Or
Why aluminium chloride in air?
Describe the shapes of BF3 and 
. Assign the hybridization of boron in these species ?
Long Answer TypeSuggest a reason why the B - F bond lengths in BF3 (130 pm) and 
 (143 pm) differ?
Or
Why B - F bond length in BF3 is smaller than the expected value?
In BF3, boron is sp2 hybridised and therefore BF3 is a planar molecule. It has a vacant 2p-orbital. F-atom has three lone pairs of electrons. In BF3 molecule, one 2p-orbital of fluorine atom overlaps sidewise with empty 2p-orbtial of boron to form 
 back bonding (back donation) in which the lone pair is transferred from F to B as shown.
As a result of this back bonding (or black donation), the B-F bond acquires some double bond character.Â
On the other hand in 
 ion,  boron is sp3 hybridised and therefore 
 is a tetrahedral molecule. B in 
 ion does not have vacant p-orbital available to accept the electrons donated by the F atom. Hence 
 ion, B -F is a purely single bond. Since double bonds are shorter than single bonds, therefore B-F bond length in BF3 is shorter (130 pm) than B-F bond length (143 pm) in  [BF4]–.
Short Answer Type
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