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Terbium

Element 65 · Lanthanide

Specimen

Atomic number
65
Atomic mass
158.93
State at room temperature
Solid
Melting point
1,356 °C
Boiling point
3,230 °C
Density
8.23 g/cm³
Discovered
1843

Atomic mass from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Not needed, little harm known. Terbium has no known function in the body. The oral dose of terbium chloride that killed half the rats in a test was 5.1 g per kg of body weight. Few other studies exist. 34

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The atom

Tb
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 18
4 (N) 27
5 (O) 8
6 (P) outermost 2
Total65

Configuration [Xe] 4f⁹ 6s²

4f ↑ ↓ ↑ ↓ ↑ ↑ ↑ ↑ ↑
6s ↑ ↓
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 65 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Xe core, with one arrow per electron.

Related elements

Lanthanides
La Lanthanum Ce Cerium Pr Praseodymium Nd Neodymium Pm Promethium Sm Samarium Eu Europium Gd Gadolinium Dy Dysprosium Ho Holmium Er Erbium Tm Thulium Yb Ytterbium Lu Lutetium

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

    The atomic mass shown for the 84 elements that have a standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    Toxicology Excellence for Risk Assessment (TERA), for the US Bureau of Land Management, 1999. Development of Reference Doses and Reference Concentrations for Lanthanides , Section 2.4 (oral toxicity data in experimental animals).

    • 5100 mg/kg for terbium chloride
  4. 4

    Royal Society of Chemistry, 2026. Terbium - Element information, properties and uses .

    • Terbium has no known biological role. It has low toxicity.
  5. 5

    National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

    Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.