Animated Solution for Chemistry - d and f-Block Elements: The incorrect statement is :

Manganate vs Permanganate

When studying the d-block elements, the compounds of manganese often steal the spotlight due to their vibrant colours and fascinating magnetic properties. Two of the most famous ions are the manganate ion ($Mn{O}_4^{2-}$) and the permanganate ion ($Mn{O}_4^{-}$). At first glance, they look incredibly similar. Both feature a central manganese atom surrounded by four oxygen atoms in a perfect tetrahedral geometry. However, a deeper look into their electronic structures reveals a world of differences.

The key to unlocking the differences between these two ions lies in the oxidation state of the central manganese atom. Let's calculate it for both.

For the manganate ion ($Mn{O}_4^{2-}$), the sum of the oxidation states must equal the overall charge of $-2$. Since each oxygen atom has an oxidation state of $-2$, we get:

For the permanganate ion ($Mn{O}_4^{-}$), the overall charge is $-1$, giving us:

Now, let's look at the electronic configuration. The ground state of a neutral manganese atom is $[Ar]3d^{5}4s^2$. When manganese is in the $+6$ oxidation state (as in manganate), it loses six electrons, leaving it with a configuration of $3d^1$. On the other hand, in the $+7$ oxidation state (as in permanganate), it loses all seven of its valence electrons, resulting in a $3d^0$ configuration.

The Key Difference

This difference in electronic configuration directly dictates the magnetic behavior of the ions. The manganate ion, with its $3d^1$ configuration, possesses exactly one unpaired electron. This makes the manganate ion paramagnetic.

Conversely, the permanganate ion has a $3d^0$ configuration. With absolutely zero unpaired electrons, it is strictly diamagnetic. This is a classic trap in many competitive exams, where students assume that because both ions are highly coloured, they must both have unpaired d-electrons.

Speaking of colour, manganate is known for its striking green hue, while permanganate is famous for its deep, intense purple colour. The intense purple of permanganate is particularly interesting because it occurs despite having no d-electrons; it is a result of Ligand-to-Metal Charge Transfer (LMCT).

Furthermore, the bonding in both ions is quite similar. The double bonds between manganese and oxygen are formed through $\pi$-bonding. Specifically, this involves the overlap of the filled $2p$-orbitals of the oxygen atoms with the empty $3d$-orbitals of the manganese atom, creating strong $p\pi -d\pi$ bonds.

By systematically analyzing the properties of both ions, we can easily evaluate the given statements. The manganate ion is indeed green and paramagnetic, while the permanganate ion is purple and diamagnetic. Both share a tetrahedral geometry and $p\pi -d\pi$ bonding. Therefore, the statement claiming that both ions are paramagnetic is fundamentally incorrect.