---
title: "Terbium (Tb): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/terbium.html
description: "Terbium (Tb), element 65: atomic mass 158.93, electron configuration [Xe] 4f⁹ 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
---
65Tb158.93

# Terbium (Tb) – element 65

Terbium is a chemical element with the symbol **Tb** and atomic number **65**. It is a lanthanide in group 3 (lanthanides), period 6 of the periodic table (f-block), and is a solid at room temperature.

Terbium (Tb) has atomic number 65, atomic mass 158.93 u and electron configuration [Xe] 4f9 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)

## Terbium facts

| Symbol | Tb |
| --- | --- |
| Atomic number | 65 |
| Atomic mass | 158.93 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 4f9 |
| Noble-gas notation | [Xe] 4f9 6s2 |
| Electrons per shell | 2, 8, 18, 27, 8, 2 |

## Bohr model and shells

Terbium has 65 electrons in 6 shells: 2, 8, 18, 27, 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 | 1629 K (1355.8 °C) |
| --- | --- |
| Boiling point | 3396 K (3122.8 °C) |
| Density | 8.23 g/cm³ |
| Electronegativity (Pauling) | 1.1 |
| Electron affinity | 112.4 kJ/mol |
| Ionization energies | 565.8, 1110, 2114 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 28.91 J/(mol·K) |
| Discovered by | Carl Gustaf Mosander |

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 Tb.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of terbium?

The atomic mass of terbium is 158.93 u, so one mole of terbium atoms weighs 158.93 g.

### What is the electron configuration of terbium?

Terbium has 65 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁹, or [Xe] 4f⁹ 6s² in noble-gas notation. Electrons per shell: 2, 8, 18, 27, 8, 2.

### Is terbium a metal?

Yes. Terbium is a lanthanide.

### Where is terbium on the periodic table?

Terbium 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.