Describe the chemical properties of the elements of group $13$.

(N/A) Due to the small size of boron,the sum of its first three ionization enthalpies is very high. This prevents it from forming $3+$ ions and forces it to form only covalent compounds.
As we move from $B$ to $Al$,the sum of the first three ionization enthalpies of $Al$ decreases considerably,allowing it to form $Al^{3+}$ ions. Aluminium is a highly electro-positive metal.
Down the group,due to the poor shielding effect of intervening $d$ and $f$ orbitals,the increased effective nuclear charge holds $ns$ electrons tightly (inert pair effect),restricting their participation in bonding.
Consequently,only $p$-orbital electrons may be involved in bonding. In $Ga$,$In$,and $Tl$,both $+1$ and $+3$ oxidation states are observed.
The relative stability of the $+1$ oxidation state increases for heavier elements: $Al < Ga < In < Tl$.
In thallium,the $+1$ oxidation state is predominant,while the $+3$ oxidation state is highly oxidizing.
Compounds in the $+1$ oxidation state are more ionic than those in the $+3$ oxidation state.
In the trivalent state,the central atom in these compounds (e.g.,boron in $BCl_3$) has only six electrons. Such electron-deficient molecules act as Lewis acids.
The tendency to act as a Lewis acid decreases down the group. For example,$BCl_3$ accepts a lone pair from ammonia to form $BCl_3 \cdot NH_3$.