Discuss the characteristics of group 13 elements in terms of :
(i) Electronegativity        
(ii) Nature of bonds        
(iii) Oxidation states. 

(i) Electronegativity: There is no regular change in electronegativity on moving down the group. Down the group, electronegativity first decreases from B to Al and then increases marginally. This is because of the discrepancies in atomic size of the elements.

(ii) Nature of bonds: According to Fajan’s rule, the smaller the cation, the greater is its tendency to form covalent compounds. Thus, with the increase of M³⁺ ionic radii down the group from B³⁺ to Tl³⁺, the tendency of these ions to form covalent compounds decreases. Thus boron forms mostly covalent compounds while other members form ionic compounds also.

(iii) Oxidation states: The general electronic configuration of group 13 elements [Noble gas] is ns² np¹, so these elements are expected to show a uniform oxidation state of + 3. Boron and aluminium show an oxidation state of +3 only, but gallium, indium and thallium, however, show oxidation states of + 1 and +3.