69TmThulium168.934222[Xe] 4f¹³ 6s²
lanthanide

Thulium

Thulium is a chemical element with symbol Tm and atomic number 69. It is the thirteenth and antepenultimate (third-last) element in the lanthanide series. Like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other compounds.

Properties

At a glance

Atomic number
69
Atomic mass
168.934222 u
Phase
Solid
Density
9.32 g/cm³
Melting point
1,818 K
Boiling point
2,223 K
First ionization energy
596.7 kJ/mol
Electronegativity
1.25
Electron affinity
99 kJ/mol
Molar heat capacity
27.03 J/(mol·K)
Period
6
Appearance
silvery gray

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

Electronic structure

Thulium’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…

69 protons100 neutrons

Thulium-169: 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, thulium 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

Tm

TmNeutral atom · no charge

A neutral thulium atom. Removing its first electron takes 597 kJ/mol.

Thulium’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 2× 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). Thulium’s first electron takes about 6.2 eV.
1001,00010,000100,0001,000,00010,000,000Shell 5Shell 4Shell 3Shell 2×2×1.1×1.7×2.2×415101520253035404550556065
Show the values as a table
ElectronShellEnergy (kJ/mol)× previousValue
16597–Measured
261,1642Estimated
352,2832Estimated
454,0921.8Estimated
556,3101.5Estimated
659,4561.5Calculated
7511,1921.2Calculated
8512,8331.1Calculated
9515,4381.2Calculated
10517,3671.1Calculated
11419,7791.1Calculated
12423,0601.2Calculated
13426,4371.1Calculated
14428,4631.1Calculated
15430,5861.1Calculated
16433,9631.1Calculated
17437,3401.1Calculated
18440,9101.1Calculated
19444,3831.1Calculated
20447,8571.1Calculated
21451,1371.1Calculated
22454,9971.1Calculated
23458,1811.1Calculated
24479,6001.4Calculated
25483,5561Calculated
26487,8981.1Calculated
27492,4331.1Calculated
28496,8711Calculated
294101,3101Calculated
304107,0991.1Calculated
314111,6341Calculated
324116,4581Calculated
334121,0891Calculated
344139,1321.1Calculated
354143,7631Calculated
364148,7801Calculated
374153,5081Calculated
384164,6041.1Calculated
394169,9111Calculated
404182,2611.1Calculated
414187,6831Estimated
423318,2091.7Calculated
433328,9181Calculated
443340,4001Calculated
453352,4611Calculated
463364,2321Calculated
473375,8101Calculated
483393,1781Calculated
493405,1421Calculated
503418,2641Calculated
513430,4211Calculated
523464,2871.1Calculated
533474,9011Calculated
543486,6721Calculated
553497,5751Calculated
563533,2741.1Calculated
573545,7211Calculated
583569,3601Calculated
593581,1311Calculated
6021,287,7902.2Calculated
6121,317,1211Calculated
6221,349,6371Calculated
6321,379,7401Calculated
6421,511,2501.1Calculated
6521,547,2391Calculated
6621,592,9731Calculated
6721,622,3371Calculated
6816,557,6504Calculated
6916,694,8711Calculated

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?

ThuliumOther lanthanidesOther elements

Density

9.32 g/cm³30th highest of 99

Tm

Melting point

1,818 K22nd highest of 96

Tm

Boiling point

2,223 K43rd lowest of 97

Tm

Electronegativity

1.2527th lowest of 96

Tm

First ionization energy

597 kJ/mol33rd lowest of 99

Tm

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.