65TbTerbium158.925352[Xe] 4f⁹ 6s²
lanthanide

Terbium

Terbium is a chemical element with symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime and euxenite.

Properties

At a glance

Atomic number
65
Atomic mass
158.925352 u
Phase
Solid
Density
8.23 g/cm³
Melting point
1,629 K
Boiling point
3,396 K
First ionization energy
565.8 kJ/mol
Electronegativity
1.1
Electron affinity
112.4 kJ/mol
Molar heat capacity
28.91 J/(mol·K)
Period
6
Appearance
silvery white

Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.

Electronic structure

Terbium’s orbitals use a hydrogen-like approximation. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.

Electrons by shell
Electron configuration

54 is the [Xe] core total across five shells.

Preparing the orbital view…

65 protons94 neutrons

Terbium-159: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.

States of matter

Turn up the heat

298 KK stands for kelvin, the temperature scale used in science. It starts at absolute zero (0 K), the coldest temperature possible, so it has no negative numbers and no degree sign.

A step of 1 K is the same size as 1 °C, so the two scales are always 273.15 apart. Fahrenheit is different: its degrees are smaller and it starts elsewhere, so water freezes at 273.15 K, 0 °C and 32 °F.25 °C · 77 °FSolid

At this temperature, terbium is a solid.

At normal atmospheric pressure (1 atm). The temperature scale is logarithmic. The particle box is schematic: real samples hold vastly more atoms, and spacing and speeds are not to scale.

Ionization energy

Pull the electrons off

Tb

TbNeutral atom · no charge

A neutral terbium atom. Removing its first electron takes 566 kJ/mol.

Terbium’s outer shell holds 2 electrons. Electron 3 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 1.9× as much energy as the one before. Each dashed line on the chart marks another jump, into a shell even closer to the nucleus.

Shell 1Shell 2Shell 3Shell 4Shell 5Shell 6MeasuredEstimated or calculatedEnergy in kJ/molkJ/mol (kilojoules per mole) is the energy to remove that electron from every atom in a mole of them: about 602 sextillion (6.02 × 10²³) atoms. For a single atom, divide by 96.485 to get electronvolts (eV). Terbium’s first electron takes about 5.9 eV.
1001,00010,000100,0001,000,00010,000,000Shell 5Shell 4Shell 3Shell 2×1.9×1.1×1.7×2.2×4.115101520253035404550556065
Show the values as a table
ElectronShellEnergy (kJ/mol)× previousValue
16566–Measured
261,1112Estimated
352,1051.9Estimated
453,7951.8Estimated
556,4161.7Estimated
658,6841.4Calculated
7510,4201.2Calculated
8512,0611.2Calculated
9513,7971.1Calculated
10516,2101.2Calculated
11417,9461.1Calculated
12420,8411.2Calculated
13424,1211.2Calculated
14426,3401.1Calculated
15428,3671.1Calculated
16431,3581.1Calculated
17434,5421.1Calculated
18437,9191.1Calculated
19441,1611.1Calculated
20459,1461.4Calculated
21462,8121.1Calculated
22466,5751.1Calculated
23470,6271.1Calculated
24474,4871.1Calculated
25478,7321.1Calculated
26483,5561.1Calculated
27487,7051Calculated
28492,0471Calculated
29496,1961Calculated
304112,4051.2Calculated
314116,5541Calculated
324121,1861Calculated
334125,5271Calculated
344134,4041.1Calculated
354139,2281Calculated
364150,4211.1Calculated
374155,3801Estimated
383265,3351.7Calculated
393275,1761Calculated
403285,6931Calculated
413296,9821Calculated
423307,6921Calculated
433318,4021Calculated
443333,6461Calculated
453344,7421Calculated
463356,8031Calculated
473367,9951Calculated
483399,3531.1Calculated
493409,2911Calculated
503420,1941Calculated
513430,3251Calculated
523459,2701.1Calculated
533470,5591Calculated
543492,3651Calculated
553503,3641Calculated
5621,126,2732.2Calculated
5721,153,6751Calculated
5821,184,0681Calculated
5921,212,1451Calculated
6021,317,7971.1Calculated
6121,351,0841Calculated
6221,392,6691Calculated
6321,420,3631Calculated
6415,764,1424.1Calculated
6515,890,4391Calculated

Successive ionization energies of gas-phase atoms and ions from the NIST Atomic Spectra Database. Solid bars are measured; hatched bars were estimated from nearby measurements or calculated from quantum theory, as is usual for highly charged ions. Electrons are taken from the outermost shell first, a simplification: electrons in different subshells of the same shell also differ in energy. On the log scale each gridline is 10 times the one below.

Compared with other elements

How does it compare?

TerbiumOther lanthanidesOther elements

Density

8.23 g/cm³41st highest of 99

Tb

Melting point

1,629 K32nd highest of 96

Tb

Boiling point

3,396 K28th highest of 97

Tb

Electronegativity

1.113th lowest of 96

Tb

First ionization energy

566 kJ/mol20th lowest of 99

Tb

Elements 1–99 from the reference data; heavier elements are left out because only a few atoms have ever been made, so their bulk properties are predictions. First ionization energies come from NIST. Density uses a logarithmic scale, because gases are around a thousand times less dense than solids; gas densities are at 0 °C and 1 atm. Melting and boiling points are at normal pressure. Everyday temperatures and light sources in the pictures are approximate. Hover over a dot to see the element, or click it to compare.

Keep exploring

Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.