Animated Solution for Chemistry - Chemical Bonding and Molecular Structure: Among the following, the maximum covalent character is shown by the compound.

Have you ever wondered if an ionic bond is truly $100\%$ ionic?

It is a fascinating question. We are often taught that ionic bonds are a perfect exchange—one atom gives up an electron, and another takes it. But nature is rarely that black and white.

Enter Fajans' Rule, a beautiful concept that reveals the hidden truth: every ionic bond has a secret, partial covalent character.

Let's dive into the mechanics of this phenomenon and solve our problem step-by-step!

Imagine a tiny, highly charged positive ion (a cation) sitting next to a large, fluffy negative ion (an anion).

The cation is hungry for electrons. Because it is small and packs a dense positive charge, it exerts a massive gravitational-like pull on the electron cloud of the neighboring anion.

This ability to distort the anion's electron cloud is called Polarizing Power.

When the electron cloud gets pulled towards the cation, the electrons are no longer perfectly localized on the anion. They start to be shared between the two nuclei.

And what do we call the sharing of electrons? A covalent bond!

Therefore, Fajans' Rule states a simple but profound truth: The greater the polarizing power of the cation, the greater the covalent character of the ionic bond.

Now, let's look at the compounds given in our problem: ${\text{SnCl}}_2$, ${\text{AlCl}}_3$, ${\text{MgCl}}_2$, and ${\text{FeCl}}_2$.

Notice a pattern? The anion in every single option is the chloride ion (${\text{Cl}}^{-}$).

Since the anion is identical across the board, it cannot be the deciding factor. The secret to the maximum covalent character must lie hidden within the cations.

Let's isolate our suspects: ${\text{Sn}}^{2+}$, ${\text{Al}}^{3+}$, ${\text{Mg}}^{2+}$, and ${\text{Fe}}^{2+}$.

To find the cation with the highest polarizing power, we need to look at its charge density.

Charge density is directly proportional to the positive charge and inversely proportional to the size of the ion.

Let's evaluate the charges: - Tin ($\text{Sn}$) is in a $+2$ oxidation state. - Magnesium ($\text{Mg}$) is in a $+2$ oxidation state. - Iron ($\text{Fe}$) is in a $+2$ oxidation state. - Aluminum ($\text{Al}$) is in a $+3$ oxidation state.

Aluminum clearly stands out from the crowd. It carries a $+3$ charge, which is significantly higher than the $+2$ charge of the others.

Because ${\text{Al}}^{3+}$ has the highest positive charge and a relatively small ionic radius, it possesses the maximum charge density among the given options.

This immense charge density gives ${\text{Al}}^{3+}$ an unparalleled polarizing power. It aggressively distorts the electron cloud of the chloride ions surrounding it.

This intense sharing of the electron cloud results in the highest covalent character.

Therefore, the compound with the maximum covalent character is undoubtedly ${\text{AlCl}}_3$.

I know this might seem like a lot of theory for a single question, but understanding the why behind Fajans' Rule unlocks the ability to solve hundreds of similar problems.

Keep visualizing the electron clouds, keep questioning the absolute nature of bonds, and you will master chemical bonding!