Would you expect \(\mathrm{Fe}^{3+}\) or \(\mathrm{Fe}^{2+}\) to be the stronger Lewis acid? Explain.

Short Answer

Expert verified
In the given species, \(\mathrm{Fe}^{3+}\) has a higher positive charge and electron configuration of \([Ar]~3d^5\) compared to the \(\mathrm{Fe}^{2+}\) ion with an electron configuration of \([Ar]~3d^6\). Since both ions have empty 4s orbitals, the higher positive charge of \(\mathrm{Fe}^{3+}\) results in a stronger attraction to electron pairs. Therefore, \(\mathrm{Fe}^{3+}\) would be the stronger Lewis acid.

Step by step solution

01

Understanding Lewis acids

A Lewis acid is a chemical species that can accept an electron pair from a Lewis base in a chemical reaction. In other words, Lewis acids have an empty orbital that can accommodate a pair of electrons donated by a Lewis base.
02

Analyzing \(\mathrm{Fe}^{3+}\) and \(\mathrm{Fe}^{2+}\) ions

To determine which species is the stronger Lewis acid, we need to compare their charge and electron configurations. The electron configuration for a neutral Fe atom is \([Ar] 4s^2~3d^6\). When Fe loses 2 electrons and becomes the \(\mathrm{Fe}^{2+}\) ion, its electron configuration becomes \([Ar]~3d^6\). When it loses 1 more electron, forming the \(\mathrm{Fe}^{3+}\) ion, its electron configuration is \([Ar]~3d^5\).
03

Comparing charge and electron configurations

The \(\mathrm{Fe}^{3+}\) ion has one more positive charge than the \(\mathrm{Fe}^{2+}\) ion. The increased positive charge attracts the negatively charged electron pairs of Lewis bases more strongly. Additionally, both \(\mathrm{Fe}^{3+}\) and \(\mathrm{Fe}^{2+}\) have empty 4s orbitals that can accommodate electron pairs. Their 3d orbitals are partially filled, but the higher positive charge on the \(\mathrm{Fe}^{3+}\) ion results in a stronger attraction to electron pairs.
04

Conclusion

Based on the higher positive charge and similarity in electron configurations, we would expect the \(\mathrm{Fe}^{3+}\) ion to be the stronger Lewis acid, as it has a greater capacity to attract and accept electron pairs from Lewis bases.

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