Terbium (Tb)
Terbium is element 65, a lanthanide in the lanthanide series (period 6). A neutral atom has 65 protons, 94 neutrons and 65 electrons, 2 of them valence electrons.
Lanthanide- Atomic number
- 65
- Atomic mass
- 158.93 u
- Valence electrons
- 2*
- Protons · neutrons
- 65 · 94
- Electrons per shell
- 2, 8, 18, 27, 8, 2
- At room temperature
- solid
Bohr model of terbium
The Bohr model draws terbium as a nucleus of 65 protons and 94 neutrons, with its 65 electrons on 6 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 27 in shell 4, 8 in shell 5, 2 in shell 6. Press Build the atom to watch the shells fill from the inside out. The outer ring (the P shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of terbium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁹
Short form (noble gas notation): [Xe] 6s² 4f⁹. The [Xe] stands for the electrons of xenon, the noble gas before it.
How many valence electrons does terbium have?
Terbium has 2 valence electrons.
Terbium is a lanthanide, so its valence electrons are less clear-cut than for main-group elements. It has 2 electrons in its outermost shell (shell 6), and electrons in its inner f and d subshell can also take part in bonding.
Protons, neutrons and electrons
| Protons | 65 | equal to the atomic number |
|---|---|---|
| Electrons | 65 | equal to the protons in a neutral atom |
| Neutrons | 94 | mass number 159 − 65 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Terbium properties
| Symbol | Tb |
|---|---|
| Category | Lanthanide |
| Group · period · block | — · 6 · f |
| Atomic mass | 158.93 u |
| State at 25 °C | solid |
| Melting point | 1,629 K (1,360 °C, 2,470 °F) |
| Boiling point | 3,503 K (3,230 °C, 5,850 °F) |
| Density | 8.23 g/cm³ |
| Electronegativity (Pauling) | — |
| Atomic radius | 221 pm |
| First ionization energy | 5.864 eV |
| Electron affinity | — |
| Oxidation states | +3 |
| Common ion charge | +3 |
| Discovered | 1843 by Carl Gustaf Mosander |
Where terbium sits on the periodic table
Lanthanides: Lanthanum, Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium.
Questions about terbium
How many valence electrons does terbium have?
Terbium has 2 valence electrons in its outer shell; inner d or f electrons can also bond.
How many protons, neutrons and electrons does terbium have?
A neutral terbium atom has 65 protons and 65 electrons. Its most common form has about 94 neutrons (mass number 159 − 65 protons).
What is the electron configuration of terbium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁹, written in short form as [Xe] 6s² 4f⁹.
What does the Bohr model of terbium look like?
A nucleus of 65 protons and 94 neutrons, circled by 6 electron shells holding 2, 8, 18, 27, 8, 2 electrons.
What is the atomic number of terbium?
65. The atomic number is the number of protons in the nucleus, and it is what makes an atom terbium.