Terbium (Tb)
Element 65 · Lanthanide · atomic mass 158.93 u · f-block, period 6
Electron shells: 2, 8, 18, 27, 8, 2
Terbium provides the green in trichromatic lighting and displays. It also changes shape in a magnetic field, which lets flat surfaces be turned into loudspeakers.
Terfenol-D alloy physically changes length in a magnetic field, turning any hard surface into a speaker.
- Atomic number
- 65
- Atomic mass
- 158.93 u
- Electron configuration
- [Xe] 6s² 4f⁹
- Group · period · block
- f-block · 6 · f
- Oxidation states
- +3
- Electronegativity
- Not measured
- Melting point
- 1,356 °C
- Boiling point
- 3,230 °C
- Density
- 8.23 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-white metal
- Discovered
- Carl Gustaf Mosander, 1843
65 protons, and 65 electrons when neutral
IUPAC standard atomic weight
Shown in the strip below the table
What Terbium is used for
- Green phosphors in displays and lamps
- Terfenol-D magnetostrictive actuators
- Solid-state devices and sensors
- Fuel cell stabilisers
Atomic structure of Terbium
A neutral terbium atom has 65 protons and 65 electrons. Its most common isotope carries about 94 neutrons, which is where the mass number 159 comes from. Change the neutron count and you have a different isotope of terbium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 27, 8, 2. In orbital notation that is [Xe] 6s² 4f⁹. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Terbium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Terbium sits in the periodic table
The first f-block row, elements 57-71. Chemically near-identical to each other and hard to separate, yet essential to magnets, lasers and phosphors.
- One proton lighter: Gadolinium.
- One proton heavier: Dysprosium.
Discovery and naming
Terbium was discovered by Carl Gustaf Mosander in 1843. Its name comes from Ytterby, a Swedish village, which is also why its symbol (Tb) does not match its English name.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Terbium?
The standard atomic weight of Terbium is 158.93 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Terbium have?
Terbium has 65 protons, because the atomic number is the proton count and that is what makes an atom Terbium at all. A neutral Terbium atom has the same number of electrons, 65. The neutron count varies by isotope; the most common one has about 94, since 159 − 65 = 94.
What is the electron configuration of Terbium?
The electron configuration of Terbium is [Xe] 6s² 4f⁹. Its electrons are arranged 2, 8, 18, 27, 8, 2 across 6 shells.
Is Terbium a metal?
Yes. Terbium is classified as a lanthanide, on the metallic side of the table.
What group and period is Terbium in?
Terbium sits in the f-block strip below the main table, in period 6, among the lanthanides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Terbium?
Terbium most commonly forms a 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Terbium?
Terbium melts at 1,356 °C and boils at 3,230 °C. That puts it in the solids at everyday temperatures.
What is Terbium used for?
Green phosphors in displays and lamps, Terfenol-D magnetostrictive actuators, Solid-state devices and sensors, Fuel cell stabilisers. Terbium provides the green in trichromatic lighting and displays.
Who discovered Terbium, and where does its name come from?
Terbium (Tb) was discovered by Carl Gustaf Mosander in 1843. The name comes from Ytterby, a Swedish village.