ElementsWhat is terbium?
Terbium is a soft, silvery metal of the lanthanide row.
What is terbium used for?
Green phosphors in lamps and screens, and additions to magnets and to devices that change shape in a magnetic field.
Where the name comes from
From Ytterby, the village in Sweden.
Key facts
- Symbol
- Tb
- Atomic number
- 65
- Atomic mass
- 158.92535 u
- Family
- Lanthanide
- Period
- 6
- Group
- none (f-block)
- Block
- f
- State at room temperature
- Solid
- Melting point
- 1,356 °C (1,629 K, 2,473 °F)
- Boiling point
- 3,230 °C (3,503 K, 5,846 °F)
- Density
- 8.23 g/cm³
- Electrons per shell
- 2, 8, 18, 27, 8, 2
- Electron configuration
- [Xe]6s2 4f9
- Common oxidation states
- +3
- Electronegativity (Pauling)
- no value
- First ionisation energy
- 5.864 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 221 pm
- Discovered
- 1843
Place in the periodic table
Terbium is element number 65. It sits in period 6 (row 6) of the periodic table, in the separate row of lanthanides drawn below the main table, and belongs to the f-block. Just before it comes gadolinium (64), and just after it comes dysprosium (66).
Family: Lanthanides.
Physical properties
At room temperature terbium is a solid. It melts at 1,356 °C and boils at 3,230 °C, so it stays liquid over a range of 1,874 degrees. Its density is 8.23 grams per cubic centimetre, so a one-litre block would weigh about 8.23 kilograms. By density it ranks 39th among the 96 elements with a measured value.
Inside the atom
An atom of terbium has 65 protons in its nucleus and, when neutral, 65 electrons around it. The electrons are arranged in 6 shells: 2, 8, 18, 27, 8, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Xe]6s2 4f9.
Removing one electron from an atom takes 5.864 electronvolts (about 566 kilojoules per mole). One mole of terbium weighs 158.92535 grams, so a single gram contains about 3.79 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains terbium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.