---
title: "The predicted ground-state electron configuration for chromium (\\(\\text{Cr}\\), atomic number 24) based strictly on the Aufbau principle is \\([\\text{Ar}]\\,3d^4\\,4s^2\\). However, experimental measurements show that the actual ground-state electron configuration of a neutral \\(\\text{Cr}\\) atom is \\([\\text{Ar}]\\,3d^5\\,4s^1\\). Which of the following best identifies the actual configuration and provides the correct justification for its relative stability?"
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url: "https://nerd-notes.com/ubq/119188/"
date_modified: "2026-08-19T12:39:13+00:00"
---

# The predicted ground-state electron configuration for chromium (\(\text{Cr}\), atomic number 24) based strictly on the Aufbau principle is \([\text{Ar}]\,3d^4\,4s^2\). However, experimental measurements show that the actual ground-state electron configuration of a neutral \(\text{Cr}\) atom is \([\text{Ar}]\,3d^5\,4s^1\). Which of the following best identifies the actual configuration and provides the correct justification for its relative stability?

The predicted ground-state electron configuration for chromium (\(\text{Cr}\), atomic number 24) based strictly on the Aufbau principle is \([\text{Ar}]\,3d^4\,4s^2\). However, experimental measurements show that the actual ground-state electron configuration of a neutral \(\text{Cr}\) atom is \([\text{Ar}]\,3d^5\,4s^1\). Which of the following best identifies the actual configuration and provides the correct justification for its relative stability?

- **A.** The actual configuration is \([\text{Ar}]\,3d^5\,4s^1\), because distributing six valence electrons singly across the \(3d\) and \(4s\) orbitals minimizes electron-electron repulsions, resulting in a lower overall potential energy.
- **B.** The actual configuration is \([\text{Ar}]\,3d^5\,4s^1\), because electrons in the \(3d\) subshell experience a greater effective nuclear charge than electrons in the \(4s\) subshell due to weaker shielding by core electrons.
- **C.** The actual configuration is \([\text{Ar}]\,3d^4\,4s^2\), because subshells with lower principal quantum numbers must be completely filled before electrons can occupy higher subshells.
- **D.** The actual configuration is \([\text{Ar}]\,3d^4\,4s^2\), because pairing two electrons in the \(4s\) orbital increases the Coulombic attraction between the electrons and the nucleus.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119188/*