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

Imagine a world where everything is black and white. In chemistry, we often start by learning that bonds are either purely ionic or purely covalent. But nature loves shades of gray! The truth is, no bond is $100\%$ ionic.

Even in the most classic ionic compounds, there is a hidden covalent character. This fascinating phenomenon is beautifully explained by Fajan's Rule, which reveals the secret tug-of-war happening at the atomic level.

When a positively charged cation approaches a negatively charged anion, it doesn't just sit there passively. The cation acts like a tiny magnet, pulling the fluffy, negatively charged electron cloud of the anion towards itself. This distortion of the electron cloud is called polarization.

The ability of the cation to distort the anion is known as its polarizing power. According to Fajan's Rule, polarizing power is directly proportional to the charge on the cation and inversely proportional to its size. In simple terms: a smaller cation with a higher charge packs a stronger punch!

Let's apply this to our problem. We are given four compounds: ${\text{FeCl}}_2$, ${\text{SnCl}}_2$, ${\text{AlCl}}_3$, and ${\text{MgCl}}_2$.

Notice something common? The anion in all these compounds is the chloride ion (${\text{Cl}}^{-}$). Since the anion is constant, the entire game depends on the cations. We need to compare ${\text{Fe}}^{2+}$, ${\text{Sn}}^{2+}$, ${\text{Al}}^{3+}$, and ${\text{Mg}}^{2+}$.

Look closely at the charges. Iron, tin, and magnesium all carry a $+2$ charge. But aluminum stands out with a mighty $+3$ charge!

Not only does ${\text{Al}}^{3+}$ have the highest charge, but it is also relatively small in size. This combination gives it an incredibly high charge density, making its polarizing power the strongest among the group.

Because ${\text{Al}}^{3+}$ pulls the chloride's electron cloud so fiercely, the electrons are shared more between the two atoms, leading to the maximum covalent character. Therefore, ${\text{AlCl}}_3$ is our clear winner!