---
title: "Uranium (U) — element 92"
description: "Uranium is element 92, symbol U, atomic weight 238.03. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/uranium/
site: "At One Place"
---

# Uranium (U)

**Uranium — element 92: U**

238.03 u · Actinide · period 7

Uranium-lead dating of a meteorite gave Clair Patterson the age of the Earth in 1956 — 4.55 billion years, a figure that has barely moved since. Only about 0.72% of natural uranium is the fissile uranium-235, and enriching that fraction is the single hardest step in building either a reactor or a bomb, which is why the whole non-proliferation regime is organised around centrifuges. At Oklo in Gabon, roughly 1.7 billion years ago, groundwater and a rich ore body produced natural nuclear reactors that ran intermittently for hundreds of thousands of years; the isotope ratios in the rock still show it.

## Properties

- **Atomic number:** 92
- **Symbol:** U
- **Standard atomic weight:** 238.03 u
- **Category:** Actinide
- **Period:** 7
- **Block:** f-block
- **Electron configuration:** [Rn] 7s² 5f³ 6d¹
- **Electrons per shell:** 2, 8, 18, 32, 21, 9, 2
- **Melting point:** 1,408 K — 1134.8 °C — 2074.7 °F
- **Boiling point:** 4,404 K — 4130.9 °C — 7467.5 °F
- **Density:** 18.95 g/cm³
- **Electronegativity:** 1.38 (Pauling)
- **Oxidation states:** +6, +5, +4, +3
- **Discovered:** 1789 by Martin Heinrich Klaproth

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f³ 6d¹
- **Noble gas shorthand:** [Rn] 7s² 5f³ 6d¹
- **Shells:** K: 2 · L: 8 · M: 18 · N: 32 · O: 21 · P: 9 · Q: 2

## What it is used for

- Fuel for nuclear power reactors, as enriched uranium dioxide
- Depleted uranium in armour-piercing rounds and tank armour
- Counterweights and ballast in aircraft control surfaces, historically
- Uranium glass and ceramic glazes, which fluoresce green under UV
- Uranium-lead dating, which is how the age of the Earth was established

## Hazards

- Radioactive, though uranium-238's 4.5-billion-year half-life makes it a weak emitter
- Chemically a heavy-metal kidney poison, which is the more immediate danger
- Finely divided uranium metal is pyrophoric

> Anomalous electron configuration: [Rn] 7s² 5f³ 6d¹ rather than the predicted 7s² 5f⁴. Uranium is the heaviest element that occurs on Earth in more than trace amounts.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 90 | Thorium | Th | 232.04 |
| 91 | Protactinium | Pa | 231.04 |
| 92 | Uranium ← | U | 238.03 |
| 93 | Neptunium | Np | [237] |
| 94 | Plutonium | Pu | [244] |

## Common questions

### What is the atomic number of uranium?

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

### What is the symbol for uranium?

U.

### What is the electron configuration of uranium?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f³ 6d¹, or [Rn] 7s² 5f³ 6d¹ in noble-gas shorthand.

### What is the melting point of uranium?

1,408 K — 1134.8 °C — 2074.7 °F

## Related pages

- [Thorium (Th)](https://atoneplace.net/element/thorium/)
- [Protactinium (Pa)](https://atoneplace.net/element/protactinium/)
- [Neptunium (Np)](https://atoneplace.net/element/neptunium/)
- [Plutonium (Pu)](https://atoneplace.net/element/plutonium/)

## Sources

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