---
title: "Thorium (Th): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/thorium.html
description: "Thorium (Th), element 90: atomic mass 232.04, electron configuration [Rn] 6d² 7s², group 3, period 7, f-block actinide. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
90Th232.04

# Thorium (Th) – element 90

Thorium is a chemical element with the symbol **Th** and atomic number **90**. It is a actinide in group 3 (actinides), period 7 of the periodic table (f-block), and is a solid at room temperature.

Thorium (Th) has atomic number 90, atomic mass 232.04 u and electron configuration [Rn] 6d2 7s2.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Thorium facts

| Symbol | Th |
| --- | --- |
| Atomic number | 90 |
| Atomic mass | 232.04 u (g/mol) |
| Category | actinide |
| Group | group 3 (actinides) |
| Period | 7 |
| Block | f-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 6d2 |
| Noble-gas notation | [Rn] 6d2 7s2 |
| Electrons per shell | 2, 8, 18, 32, 18, 10, 2 |

## Bohr model and shells

Thorium has 90 electrons in 7 shells: 2, 8, 18, 32, 18, 10, 2. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 2023 K (1749.8 °C) |
| --- | --- |
| Boiling point | 5061 K (4787.9 °C) |
| Density | 11.724 g/cm³ |
| Electronegativity (Pauling) | 1.3 |
| Electron affinity | 112.72 kJ/mol |
| Ionization energies | 587, 1110, 1930 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 26.23 J/(mol·K) |
| Discovered by | Jöns Jakob Berzelius |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing Th.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of thorium?

The atomic mass of thorium is 232.04 u, so one mole of thorium atoms weighs 232.04 g.

### What is the electron configuration of thorium?

Thorium has 90 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 6d², or [Rn] 6d² 7s² in noble-gas notation. Electrons per shell: 2, 8, 18, 32, 18, 10, 2.

### Is thorium a metal?

Yes. Thorium is a actinide.

### Where is thorium on the periodic table?

Thorium is in group 3 (actinides), period 7, in the f-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.