A nonmetallic element of group $-13$, used in making bullet proof vests is extremely hard solid of black colour. It can exist in many allotropic forms and has unusually high melting point. Its trifluoride acts as Lewis acid towards ammonia. The element exhibits maximum covalence of four. Identify the element and write the reaction of its trifluoride with ammonia. Explain why does the trifluoride acts as a Lewis acid.
In group-$13$, boron is only non-metallic and extremely hard and also used for making bullet proof vests. Boron exists in many allotropic forms. It usually shows high melting point and does not have' $d$-orbital.
It can show maximum covalence of 4 by using $2 s$ and $2 p$ orbitals. In trivalent halides of boron, octet of boron is not completed hence acts as Lewis acid. It reacts with Lewis base and forms adduct.
When $B_2H_6 + NH_3(excess)$ at very high temperature $(> 200\,^oC$) is formed
Explain physical and chemical properties of borax.
The Lewis acid character of boron tri halides follows the order:
The type of hybridisation of boron in diborane is
Aluminium chloride exists as dimer, $Al_2Cl_6$ in solid state as well as in soluiton of non-polar solvents such as $C_6H_6.$ When dissolved in water it gives :