Question

Amongst the following 3d-series elements, having highest value of first ionization enthalpy is ________.

• A. Zn
• B. Cu
• C. Co
• D. Sc

Hint:

Full-filled ($d^{10}s^2$) and half-filled ($d^5s^1$) configurations often show deviations in IE trends. Zn is particularly high because the electron is removed from a stable $4s^2$ shell with a high nuclear charge.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
First ionization enthalpy ($IE_1$) is the energy required to remove the first electron from an isolated gaseous atom.
In a transition series, $IE_1$ generally increases from left to right due to increasing nuclear charge and decreasing atomic size.
Step 2: Detailed Explanation:
Zinc ($Zn$) is the last element of the 3d series.
Electronic configuration of $Zn$: \( [Ar] 3d^{10} 4s^2 \).
In Zinc, both the 3d and 4s subshells are completely filled, which provides extra stability.
Additionally, because Zinc is at the end of the series, it has a high effective nuclear charge acting on its valence electrons.
Removing an electron from the stable, fully-filled \( 4s^2 \) orbital of Zinc requires significantly more energy compared to elements like $Sc, Co$, or $Cu$.
Step 3: Final Answer: Zinc ($Zn$) has the highest first ionization enthalpy among the given options.