Question

Silicon tetrachloride is readily hydrolysed while carbon tetrachloride is inert to hydrolysis. Explain.

Answer 1

CCl4 is not hydrolyzed as SiCl4 because of two reasons:

1. Carbon does not have d-orbitals because it is found in 2nd period i.e. second shell so as the 3d -orbitals are not available and so it can not expand its co-ordination no. above 4.

Since, in carbon tetrachloride (CCl4) all the valencies are satisfied, so it can not add any water molecule by any mean so the reaction becomes ;

CCl4 + H2O ---> No reaction.

While in case of silicon, it exists in period 3, which has 3d-orbitals vacant , and so it can expand its octet and can have the co-ordination no. above four so that the additional water molecule can donate a lone pair of electron to the Silicon, thus the reaction becomes:

2. Due, to smaller size of C-atom it is shielded by the larger Cl-atoms while in case of Silicon due to larger size, the extent of shielding is not that large and so attack of water is possible for hydrolysis.

Answer 2

Answer:

CCl4 can not be hydrolysed due to the absence of d-orbital in the valence shell of carbon atom (2s2 2p2). As a result, carbon can not increase its coordination number beyond four, and therefore, it can not accept electrons from water molecules.

SiCl4 on the other hand,is hydrolysed by water because silicon has vacant 3d orbital in its outermost shell. As a result, it can extend its coordination number beyond four. The vacant 3d orbital accepts lone pair electrons from water molecule forming silicic acid.

Explanation: