The ground-state electron configuration of _____is [Ar]4s13d5.
A) V
B) Mn
C) Fe
D) Cr
E) K
The correct answer and explanation is :
The correct answer is D) Cr (Chromium).
Explanation:
The electron configuration of an atom describes how the electrons are distributed in its atomic orbitals. To determine the ground-state electron configuration of an element, we use the Aufbau principle, the Pauli exclusion principle, and Hund’s rule, which tell us how electrons fill orbitals in order of increasing energy.
The elements given in the options are:
- A) V (Vanadium): Atomic number 23
- B) Mn (Manganese): Atomic number 25
- C) Fe (Iron): Atomic number 26
- D) Cr (Chromium): Atomic number 24
- E) K (Potassium): Atomic number 19
Now, let’s break down the electron configurations for each element.
Chromium (Cr) – Atomic Number 24
The expected electron configuration for Chromium (Cr), without considering exceptions, would be:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 3d⁴ (this is based on the Aufbau principle)
However, there is an exception to the expected configuration. Chromium (Cr) prefers to have a half-filled d-subshell, which provides additional stability. To achieve this, one electron from the 4s orbital is promoted to the 3d orbital. As a result, the ground-state electron configuration for Chromium is:
- [Ar] 4s¹ 3d⁵
This gives Chromium a configuration of [Ar] 4s¹ 3d⁵, where the 4s orbital has one electron, and the 3d orbital has five electrons, fully occupying the d-subshell. This configuration is more stable because the d-subshell is half-filled.
Why is this configuration important?
This half-filled d-subshell configuration provides added stability due to the symmetry and exchange energy associated with a half-filled set of degenerate orbitals. For many transition metals, configurations that lead to a stable d-subshell (such as half-filled or fully-filled) are more favorable energetically than those that do not follow this rule.
Thus, the ground-state electron configuration of Chromium (Cr) is [Ar] 4s¹ 3d⁵, which is consistent with option D).