LanthanideElement 65 · f-block

Terbium (Tb)

Terbium (Tb) is a lanthanide with atomic number 65 and a standard atomic weight of 158.93. At room temperature it is a solid that melts at 1,359 °C and boils at 3,230 °C.

65TbTerbium158.93

Atomic number

protons

Atomic weight

158.93

CIAAW 2024

Melting point

1,359 °C

1,632.15 K

Boiling point

3,230 °C

3,503.15 K

Density

8.23 g/cm³

near room temperature

Electronegativity

1.1

Pauling scale

State at 25 °C

Solid

Discovered

1843

Sweden

Terbium at a glance

Identity

Symbol	Tb
Atomic number (Z)	65
Atomic weight	158.93 ± 0.01 (CIAAW 2024)
Category	Lanthanide
Group	— (f-block: lanthanide series)
Period	6
Block	f-block
CAS number	7440-27-9

Atomic properties

Electron configuration	[Xe] 4f⁹ 6s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁹ 5s² 5p⁶ 6s²
Electrons per shell	2, 8, 18, 27, 8, 2
Oxidation states	+3 Less common: 0, +1, +2, +4
Electronegativity (Pauling)	1.1
First ionisation energy	5.864 eV (565.8 kJ/mol) 2nd: 11.513 eV · 3rd: 21.82 eV
Electron affinity	1.165 eV
Atomic radius (empirical)	175 pm
Covalent radius	168 pm
Van der Waals radius	233 pm

Physical properties

State at 25 °C	Solid
Melting point	1,359 °C · 2,478.2 °F · 1,632.15 K
Boiling point	3,230 °C · 5,846 °F · 3,503.15 K
Density	8.23 g/cm³
Specific heat capacity	0.182 J/(g·K)
Thermal conductivity	11.1 W/(m·K)
Crystal structure	Hexagonal

Isotopes & abundance

Natural occurrence	Primordial
Radioactive	No
Natural isotopes (abundance)	¹⁵⁹Tb 100%
Stable isotopes	1
Known isotopes	40
Abundance in Earth's crust	1.2 mg/kg
Abundance in seawater	0.00000014 mg/L

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Terbium electron configuration

Terbium has 65 electrons. Written in short form, its ground-state configuration is [Xe] 4f⁹ 6s² — the electrons of the noble gas xenon, plus 4f⁹ 6s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁹ 5s² 5p⁶ 6s².

4f↑↓↑↓↑↑↑↑↑

6s↑↓

Discovery and name

Discovered

1843 — Carl Gustaf Mosander · Sweden.

Name

Ytterby, Sweden.

Known for

Used in green phosphors and in Terfenol-D, an alloy that changes shape in a magnetic field.

Isotopes of terbium

Naturally occurring terbium is a mix of 1 isotope. Each has 65 protons; they differ in the number of neutrons:

Isotope	Protons	Neutrons	Natural abundance	Stability
¹⁵⁹Tb	65	94	100%	stable

40 isotopes of terbium are known in our data set (half-lives as published in nuclear data tables).

Terbium and its neighbours in the lanthanide series

Neighbouring elements in the same f-block series:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Samarium	62	150.36	1,072 °C	1,794 °C	7.52 g/cm³	1.17
Europium	63	151.96	822 °C	1,529 °C	5.24 g/cm³	1.2
Gadolinium	64	157.25	1,313 °C	3,273 °C	7.9 g/cm³	1.2
Terbium	65	158.93	1,359 °C	3,230 °C	8.23 g/cm³	1.1
Dysprosium	66	162.50	1,412 °C	2,567 °C	8.55 g/cm³	1.22
Holmium	67	164.93	1,472 °C	2,700 °C	8.8 g/cm³	1.23
Erbium	68	167.26	1,529 °C	2,868 °C	9.07 g/cm³	1.24

Frequently asked questions

6 answers

What is the atomic mass of terbium?

The standard atomic weight of terbium is 158.93 ± 0.01 (CIAAW 2024), so one mole weighs about 158.93 grams.

How many protons, neutrons and electrons does terbium have?

A neutral terbium atom has 65 protons and 65 electrons. Its most common isotope, terbium-159, has 94 neutrons.

What is the electron configuration of terbium?

[Xe] 4f⁹ 6s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁹ 5s² 5p⁶ 6s²).

What are the melting and boiling points of terbium?

Terbium melts at 1,359 °C (2,478.2 °F) and boils at 3,230 °C (5,846 °F).

Is terbium a metal?

Terbium is a metal. It is in the f-block, period 6, and is a solid at room temperature.

Who discovered terbium?

1843 — Carl Gustaf Mosander (Sweden).