Question Video: Identifying the Transition Metal with the Lowest Electron Affinity | Nagwa Question Video: Identifying the Transition Metal with the Lowest Electron Affinity | Nagwa

Question Video: Identifying the Transition Metal with the Lowest Electron Affinity Chemistry • Second Year of Secondary School

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The electron configuration for the d valence electrons of three first-row transition metals are shown. Which transition metal’s atom would you predict to have the lowest electron affinity?

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Video Transcript

The electron configuration for the d valence electrons of three first-row transition metals are shown. Which transition metal’s atom would you predict to have the lowest electron affinity?

Electron affinity is the measure of the energy released when an electron is added to a neutral atom in the gas state to form a negative ion. It is represented by 𝐸 ea and is usually measured in kilojoules per mole of atoms. A positive electron affinity value means that energy is released. A negative electron affinity value means that for the electron to be added, energy must be absorbed. We must identify the lowest electron affinity value of the three transition metals vanadium, manganese, and iron.

The transition metal with the lowest electron affinity value will require the most amount of energy to add another electron to its valence shell. The process will have a positive enthalpy change, meaning it is an endothermic process.

Let’s have a look at the general trend of electron affinity on the periodic table. In general, from left to right across a period on the periodic table, electron affinity values increase. This is because as we go left to right across a period, the number of electron shells stays the same. But the number of protons in the nucleus increases. The electrostatic attraction between the increasingly positive nucleus and the valence electrons increases. This causes the atomic radius to decrease.

In general, a newly added electron experiences more attraction to the nucleus when added to a smaller atom. We can see that the three given metals are found in period four. If we reference the trend alone, we could assume that vanadium would have the lowest electron affinity and iron would have the highest. However, we find that the overall trend alone does not explain the differences in electron affinity for these three metals. We must consider their electronic configurations.

Manganese has a highly favorable configuration with a half-filled d subshell. Forming a manganese anion by adding a sixth electron to the d subshell is so difficult that this process does not release energy but requires energy to be absorbed. Manganese has a negative electron affinity, and the addition of an electron to manganese is a highly endothermic process.

Therefore, the transition metal’s atom we would predict to have the lowest electron affinity would be manganese.

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