Question

Explain: (i) ${\left[Si{F}_6\right]}^{2-}$ is known whereas ${\left[Si{Cl}_6\right]}^{2-}$ is not known.
(ii) Boron is unable to form ${\left[{BF}_6\right]}^{3-}$ ion
(iii) conc. $H{NO}_3$ can be stored in Aluminium container.

Answer 1

a)Due to smaller size of F as compared to Cl , six small F atoms can be easily accommodated around Si atom while Cl cannot since F are present in smaller 2p orbital and Cl are present in larger 3p orbital therefore interaction of F lone pair electron with d-orbitals of silicon are stronger in F as compared Cl.

b)Boron does not have d orbitals. Because of this, it is not possible for the element to expand on its octet. This, in turn, causes the maximum covalence of boron to be restricted to 4. Beyond this value, boron will become unstable and not be able to form $[B{F}_6{]}^{3-}$ ions.

c)Nitric acid reacts with aluminium and forms a protective layer i.e. $A{l}_2{O}_3$. This protective layer makes aluminium unreactive towards $HNO_3$ and therefore, it can be stored in aluminium containers.