Animated Solution for Chemistry - p-Block Elements: The chloride that cannot get hydrolysed is

Polar Bonds and Nucleophiles

When we talk about the hydrolysis of Group 14 tetrahalides, denoted generally as ${\text{MCl}}_4$, we are essentially looking at a chemical attack. Chlorine is highly electronegative, much more so than the central metal atoms like Silicon, Tin, or Lead. This electronegativity difference creates a tug-of-war for electrons, pulling the shared electron density towards the chlorine atoms.

As a result, the central atom $\text{M}$ is left electron-deficient, acquiring a partial positive charge ($\delta +$). In the world of chemistry, a partial positive charge is like a glowing neon sign for nucleophiles—molecules that are rich in electrons and looking for a place to share them. Water (${\text{H}}_2\text{O}$) is an excellent nucleophile because the oxygen atom has two lone pairs of electrons ready to be donated.

The Need for an Empty Room

For hydrolysis to occur, the water molecule must approach the central atom and donate one of its lone pairs. This is a classic nucleophilic attack. However, there is a strict rule in quantum mechanics: you cannot put electrons where there is no space.

When the oxygen atom tries to form a coordinate bond with the central atom $\text{M}$, the central atom must temporarily expand its covalency beyond four. It needs an "empty room" to accommodate this incoming pair of electrons. In chemical terms, this empty room is a vacant d-orbital.

Carbon's Missing d-Orbitals

Let's evaluate our suspects: ${\text{SiCl}}_4$, ${\text{SnCl}}_4$, ${\text{PbCl}}_4$, and ${\text{CCl}}_4$. Silicon, Tin, and Lead belong to the 3rd, 5th, and 6th periods of the periodic table, respectively. Their valence shells have principal quantum numbers $n\ge 3$. This means they all have vacant $nd$-orbitals available. When water attacks, they happily open up these vacant d-orbitals, accept the lone pair, and undergo hydrolysis.

But what about Carbon? Carbon is a 2nd-period element ($n=2$). Its valence shell consists only of the $2s$ and $2p$ orbitals. According to the rules of quantum numbers, the $d$-subshell ($l=2$) only begins at $n=3$. There is no such thing as a $2d$ orbital!

Because Carbon lacks these vacant d-orbitals, it is strictly bound by the octet rule. It cannot expand its covalency beyond four. When the water molecule approaches ${\text{CCl}}_4$ with its lone pair, Carbon simply has nowhere to put those electrons. The attack fails, and the molecule remains unhydrolysed.

Therefore, among the given options, ${\text{CCl}}_4$ is the only chloride that cannot get hydrolysed.

Pro-Tip: While the absence of vacant d-orbitals is a primary reason for resisting hydrolysis, it's not the only one. Sometimes, a molecule might have vacant d-orbitals but still resist hydrolysis due to steric hindrance. A classic example is ${\text{SF}}_6$, where the central sulfur atom is so densely surrounded by six fluorine atoms that water molecules physically cannot reach it to initiate an attack.