---
title: "Rhodium (Rh) — element 45"
description: "Rhodium is element 45, symbol Rh, atomic weight 102.91. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/rhodium/
site: "At One Place"
---

# Rhodium (Rh)

**Rhodium — element 45: Rh**

102.91 u · Transition metal · period 5, group 9

Rhodium is the most expensive of the precious metals by a wide margin — it briefly passed $25,000 an ounce in 2021, roughly fourteen times the price of gold — because roughly 80% of it comes from South Africa, annual output is a few tonnes, and emissions rules make it hard to substitute. It is the only practical catalyst for reducing nitrogen oxides in a petrol car's exhaust, which is precisely why catalytic converter theft became an organised crime. White gold jewellery is almost always rhodium plated; when the plating wears through, the yellowish alloy underneath shows.

## Properties

- **Atomic number:** 45
- **Symbol:** Rh
- **Standard atomic weight:** 102.91 u
- **Category:** Transition metal
- **Group:** 9
- **Period:** 5
- **Block:** d-block
- **Electron configuration:** [Kr] 5s¹ 4d⁸
- **Electrons per shell:** 2, 8, 18, 16, 1
- **Melting point:** 2,237 K — 1963.8 °C — 3566.9 °F
- **Boiling point:** 3,968 K — 3694.8 °C — 6682.7 °F
- **Density:** 12.4 g/cm³
- **Electronegativity:** 2.28 (Pauling)
- **Oxidation states:** +3
- **Discovered:** 1803 by William Hyde Wollaston

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁸
- **Noble gas shorthand:** [Kr] 5s¹ 4d⁸
- **Shells:** K: 2 · L: 8 · M: 18 · N: 16 · O: 1

## What it is used for

- Catalytic converters, where it handles the nitrogen oxides
- Rhodium plating on white gold and silver jewellery
- Mirrors for searchlights and for X-ray optics
- Thermocouples for very high temperatures, alloyed with platinum
- Catalysts for making acetic acid and nitric acid

> Anomalous electron configuration: [Kr] 5s¹ 4d⁸ rather than the predicted 5s² 4d⁷.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 43 | Technetium | Tc | [97] |
| 44 | Ruthenium | Ru | 101.07 |
| 45 | Rhodium ← | Rh | 102.91 |
| 46 | Palladium | Pd | 106.42 |
| 47 | Silver | Ag | 107.87 |

## Group 9

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Rhodium sits in group 9 with cobalt, iridium, meitnerium.

## Common questions

### What is the atomic number of rhodium?

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

### What is the symbol for rhodium?

Rh.

### What is the electron configuration of rhodium?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁸, or [Kr] 5s¹ 4d⁸ in noble-gas shorthand.

### What is the melting point of rhodium?

2,237 K — 1963.8 °C — 3566.9 °F

## Related pages

- [Technetium (Tc)](https://atoneplace.net/element/technetium/)
- [Ruthenium (Ru)](https://atoneplace.net/element/ruthenium/)
- [Palladium (Pd)](https://atoneplace.net/element/palladium/)
- [Silver (Ag)](https://atoneplace.net/element/silver/)
- [Cobalt (Co)](https://atoneplace.net/element/cobalt/)
- [Iridium (Ir)](https://atoneplace.net/element/iridium/)
- [Meitnerium (Mt)](https://atoneplace.net/element/meitnerium/)

## Sources

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