---
title: "Chromium (Cr) — element 24"
description: "Chromium is element 24, symbol Cr, atomic weight 51.996. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/chromium/
site: "At One Place"
---

# Chromium (Cr)

**Chromium — element 24: Cr**

51.996 u · Transition metal · period 4, group 6

Chromium is the reason stainless steel does not rust: above about 11% it forms a self-repairing chromium oxide film a few atoms thick, and scratching it simply makes a new one. The name comes from the Greek for colour, because its compounds run through the whole spectrum — the red of ruby and the green of emerald are both trace chromium in otherwise colourless crystals. Its configuration is one of the classic textbook exceptions: [Ar] 4s¹ 3d⁵, with an electron promoted out of the 4s shell to give a half-filled d subshell, not the 4s² 3d⁴ that filling order predicts.

## Properties

- **Atomic number:** 24
- **Symbol:** Cr
- **Standard atomic weight:** 51.996 u
- **Category:** Transition metal
- **Group:** 6
- **Period:** 4
- **Block:** d-block
- **Electron configuration:** [Ar] 4s¹ 3d⁵
- **Electrons per shell:** 2, 8, 13, 1
- **Melting point:** 2,180 K — 1906.8 °C — 3464.3 °F
- **Boiling point:** 2,944 K — 2670.8 °C — 4839.5 °F
- **Density:** 7.15 g/cm³
- **Electronegativity:** 1.66 (Pauling)
- **Oxidation states:** +6, +3, +2
- **Discovered:** 1797 by Louis-Nicolas Vauquelin

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵
- **Noble gas shorthand:** [Ar] 4s¹ 3d⁵
- **Shells:** K: 2 · L: 8 · M: 13 · N: 1

## What it is used for

- Stainless steel — everything above about 11% chromium is stainless
- Chrome plating on taps, tools and older car trim
- Leather tanning, which uses chromium(III) salts
- Refractory brick lining furnaces and kilns
- Green and yellow pigments, and the red of a ruby

## Hazards

- Chromium(VI) compounds are carcinogenic by inhalation and readily absorbed through skin
- Welding or grinding stainless steel can generate hexavalent chromium fume
- Chromium(III), the form in food and supplements, is far less hazardous than chromium(VI)

> Anomalous electron configuration: [Ar] 4s¹ 3d⁵ rather than the predicted 4s² 3d⁴. A half-filled d subshell plus a half-filled s is lower in energy than the filling-order arrangement.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 22 | Titanium | Ti | 47.867 |
| 23 | Vanadium | V | 50.942 |
| 24 | Chromium ← | Cr | 51.996 |
| 25 | Manganese | Mn | 54.938 |
| 26 | Iron | Fe | 55.845 |

## Group 6

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Chromium sits in group 6 with molybdenum, tungsten, seaborgium.

## Common questions

### What is the atomic number of chromium?

24. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for chromium?

Cr.

### What is the electron configuration of chromium?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵, or [Ar] 4s¹ 3d⁵ in noble-gas shorthand.

### What is the melting point of chromium?

2,180 K — 1906.8 °C — 3464.3 °F

## Related pages

- [Titanium (Ti)](https://atoneplace.net/element/titanium/)
- [Vanadium (V)](https://atoneplace.net/element/vanadium/)
- [Manganese (Mn)](https://atoneplace.net/element/manganese/)
- [Iron (Fe)](https://atoneplace.net/element/iron/)
- [Molybdenum (Mo)](https://atoneplace.net/element/molybdenum/)
- [Tungsten (W)](https://atoneplace.net/element/tungsten/)
- [Seaborgium (Sg)](https://atoneplace.net/element/seaborgium/)

## Sources

- Official vendor product documentation — At One Place (/about/)