---
title: "The table below shows the predicted electron configurations based on the standard Aufbau principle alongside the experimentally determined ground-state electron configurations for neutral gaseous atoms of three first-row transition metals.  | Element | Atomic Number | Predicted Configuration | Observed Ground-State Configuration | | :— | :— | :— | :— | | \\(\\text{V}\\) | \\(23\\) | \\([\\text{Ar}]\\, 4s^2 3d^3\\) | \\([\\text{Ar}]\\, 4s^2 3d^3\\) | | \\(\\text{Cr}\\) | \\(24\\) | \\([\\text{Ar}]\\, 4s^2 3d^4\\) | \\([\\text{Ar}]\\, 4s^1 3d^5\\) | | \\(\\text{Cu}\\) | \\(29\\) | \\([\\text{Ar}]\\, 4s^2 3d^9\\) | \\([\\text{Ar}]\\, 4s^1 3d^{10}\\) |  Which of the following statements best explains why the ground-state electron configuration of a neutral \\(\\text{Cr}\\) atom is \\([\\text{Ar}]\\, 4s^1 3d^5\\) rather than \\([\\text{Ar}]\\, 4s^2 3d^4\\)?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/120189/"
date_modified: "2026-08-21T16:02:55+00:00"
---

# The table below shows the predicted electron configurations based on the standard Aufbau principle alongside the experimentally determined ground-state electron configurations for neutral gaseous atoms of three first-row transition metals.

| Element | Atomic Number | Predicted Configuration | Observed Ground-State Configuration |
| :— | :— | :— | :— |
| \(\text{V}\) | \(23\) | \([\text{Ar}]\, 4s^2 3d^3\) | \([\text{Ar}]\, 4s^2 3d^3\) |
| \(\text{Cr}\) | \(24\) | \([\text{Ar}]\, 4s^2 3d^4\) | \([\text{Ar}]\, 4s^1 3d^5\) |
| \(\text{Cu}\) | \(29\) | \([\text{Ar}]\, 4s^2 3d^9\) | \([\text{Ar}]\, 4s^1 3d^{10}\) |

Which of the following statements best explains why the ground-state electron configuration of a neutral \(\text{Cr}\) atom is \([\text{Ar}]\, 4s^1 3d^5\) rather than \([\text{Ar}]\, 4s^2 3d^4\)?

The table below shows the predicted electron configurations based on the standard Aufbau principle alongside the experimentally determined ground-state electron configurations for neutral gaseous atoms of three first-row transition metals.

| Element | Atomic Number | Predicted Configuration | Observed Ground-State Configuration |
| :--- | :--- | :--- | :--- |
| \(\text{V}\) | \(23\) | \([\text{Ar}]\, 4s^2 3d^3\) | \([\text{Ar}]\, 4s^2 3d^3\) |
| \(\text{Cr}\) | \(24\) | \([\text{Ar}]\, 4s^2 3d^4\) | \([\text{Ar}]\, 4s^1 3d^5\) |
| \(\text{Cu}\) | \(29\) | \([\text{Ar}]\, 4s^2 3d^9\) | \([\text{Ar}]\, 4s^1 3d^{10}\) |

Which of the following statements best explains why the ground-state electron configuration of a neutral \(\text{Cr}\) atom is \([\text{Ar}]\, 4s^1 3d^5\) rather than \([\text{Ar}]\, 4s^2 3d^4\)?

- **A.** The \([\text{Ar}]\, 4s^1 3d^5\) configuration is favored because the \(3d\) subshell penetrates closer to the nucleus than the \(4s\) subshell, resulting in a higher effective nuclear charge experienced by all valence electrons.
- **B.** The \([\text{Ar}]\, 4s^1 3d^5\) configuration is favored because having \(5\) singly occupied degenerate \(3d\) orbitals completely eliminates electrostatic electron-electron repulsions among all valence electrons.
- **C.** The \([\text{Ar}]\, 4s^1 3d^5\) configuration is favored because the small energetic penalty of promoting an electron between the closely spaced \(4s\) and \(3d\) subshells is offset by the reduction in electron-electron repulsion from unpairing the \(4s\) electrons.
- **D.** The \([\text{Ar}]\, 4s^1 3d^5\) configuration is favored because the half-filled \(3d\) subshell completely shields the remaining \(4s\) electron from the nuclear charge, significantly lowering the potential energy of the \(4s\) orbital.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120189/*