Terbium (Tb)
Element 65 · Lanthanide · Solid at 25 °C · Period 6 (f-block)
Terbium supplies brilliant green phosphors for displays and low-energy lighting.
On the periodic table, terbium sits in the f-block in period 6. It is one of 15 elements classified as a lanthanide, and at room temperature (25 °C) it is a solid.
The lanthanides — often called rare-earth elements — fill the 4f orbitals along the detached row at the bottom of the table. Chemically they are remarkably alike, almost all preferring the +3 oxidation state, which historically made them very hard to separate. Today they are anything but obscure: strong permanent magnets, screen phosphors, and lasers depend on them.
Properties of terbium
| Atomic number (Z) | 65 |
|---|---|
| Symbol | Tb |
| Atomic mass | 158.93 |
| Category | Lanthanide |
| Group | — (f-block, associated with group 3) |
| Period | 6 |
| Block | f-block |
| Metal / nonmetal | Metal |
| State at 25 °C | Solid |
| Electron configuration | [Xe] 4f9 6s2 |
| Electronegativity (Pauling) | 1.2 |
| Melting point | 1,356 °C (1,629.15 K / 2,472.8 °F) |
| Boiling point | 3,230 °C (3,503.15 K / 5,846 °F) |
| Density | 8.23 g/cm³ |
Position in the periodic table
Terbium belongs to the lanthanides, the detached f-block row shown beneath the main table. These elements all fit between groups 2 and 4 of period 6, and are pulled out into their own row only to keep the table a manageable width.
Physical properties
Terbium melts at 1,356 °C (1,629.15 K / 2,472.8 °F) and boils at 3,230 °C (3,503.15 K / 5,846 °F), giving it a liquid range of about 1,874 °C at standard pressure.
Its density is 8.23 g/cm³.
See also: the interactive periodic table, how to read the periodic table, periodic trends.