Discuss similarities in properties among the group 13 elements. 

(i) All 13 group elements have three electrons such as   in the outermost orbit. 
(ii) All these elements show a group valency of three. The sum of the first three ionisation energies of these elements is very high. Thus the formation of their trivalent ions (M³⁺) would require very high energy. Hence, their compounds when anhydrous are either essentially covalent or contain an appreciable amount of covalent character.

(iii) These elements are not strongly electropositive.
(iv) They readily form tri-covalent compounds, which are usually trigonal planar in shape.
(v) These elements have only three valence electrons, thus even after the formation of three covalent bonds, they possess only six valence electrons i.e. they are electron deficient compounds. For example.

(vi) In their compounds they have only six valency electrons i.e. they require a pair of electrons to complete their octets. Thus their compounds act as Lewis acids or electron pair acceptors. For example,

(vii) Many of these ‘donor-acceptor’ compounds are known: they are sometimes known as ‘adducts.’
(viii) All the metal ions exist in the hydrated state.
(ix) They form complexes, 4-coordinate and tetrahedral for boron [e.g. (BF₄)^–] and often 60-coordinate and octahedral for the other elements [e.g.(AlF₆)^–].