---
title: "Thulium (Tm): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/thulium.html
description: "Thulium (Tm), element 69: atomic mass 168.93, electron configuration [Xe] 4f¹³ 6s², group 3, period 6, f-block lanthanide. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
69Tm168.93

# Thulium (Tm) – element 69

Thulium is a chemical element with the symbol **Tm** and atomic number **69**. It is a lanthanide in group 3 (lanthanides), period 6 of the periodic table (f-block), and is a solid at room temperature.

Thulium (Tm) has atomic number 69, atomic mass 168.93 u and electron configuration [Xe] 4f13 6s2.

[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)

## Thulium facts

| Symbol | Tm |
| --- | --- |
| Atomic number | 69 |
| Atomic mass | 168.93 u (g/mol) |
| Category | lanthanide |
| Group | group 3 (lanthanides) |
| Period | 6 |
| Block | f-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f13 |
| Noble-gas notation | [Xe] 4f13 6s2 |
| Electrons per shell | 2, 8, 18, 31, 8, 2 |

## Bohr model and shells

Thulium has 69 electrons in 6 shells: 2, 8, 18, 31, 8, 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 | 1818 K (1544.8 °C) |
| --- | --- |
| Boiling point | 2223 K (1949.8 °C) |
| Density | 9.32 g/cm³ |
| Electronegativity (Pauling) | 1.25 |
| Electron affinity | 99 kJ/mol |
| Ionization energies | 596.7, 1160, 2285 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 27.03 J/(mol·K) |
| Discovered by | Per Teodor Cleve |

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 Tm.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of thulium?

The atomic mass of thulium is 168.93 u, so one mole of thulium atoms weighs 168.93 g.

### What is the electron configuration of thulium?

Thulium has 69 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹³, or [Xe] 4f¹³ 6s² in noble-gas notation. Electrons per shell: 2, 8, 18, 31, 8, 2.

### Is thulium a metal?

Yes. Thulium is a lanthanide.

### Where is thulium on the periodic table?

Thulium is in group 3 (lanthanides), period 6, 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.