Thulium Properties (25 Facts You Should Know)

Thulium element has been identified by symbol Tm. It is the thirteenth and third last element in the lanthanide series. Let us discuss all the chemical properties of thulium.

Pure thulium metal is a bright silvery luster. It is not a pure form of an element it is always observed in rare earth metals form.  It is not a hard metal and therefore it can be cut easily into pieces.

Tm shows malleable and ductile in nature. Its radioisotopes are used in industrial radiography. In this article, we will discuss all the chemical properties of thulium like boiling point, melting point, oxidation state, electronic configuration and many more.

Thulium symbol

The symbol of thulium is Tm.

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Symbol of Thulium

Thulium group in periodic table

Thulium belongs to the lanthanides group of periodic table.

Thulium period in periodic table

Thulium belongs to the 6th period of the periodic table. As it is present in the 6th row of the periodic table.

Thulium block in periodic table

Thulium belongs to the f block as the valence electrons are present in the 4f orbital.

Thulium atomic number

The atomic number of Thulium is 69. As thulium has a total of 69 protons.

Thulium atomic weight

The atomic weight of thulium is 168.89 g.mol-1.

Thulium Electronegativity according to Pauling

According to Pauling electronegativity of thulium is 1.2 it has less ability to attract electrons.

Thulium atomic density

The atomic density of thulium is 9.3 g cm-1. Meaning that the weight of an atom per unit volume of thulium will be calculated as 9.3.

Thulium melting point

The melting point of thulium is 1545oC. At that temperature, solid thulium is converted into liquid.

Thulium boiling point

The boiling point of thulium is 1947oC. At that temperature thulium vapour pressure is equal to its surrounding temperature and liquid thulium is converted into its vapour.

Thulium Vander Waals radius

Thulium does not have a Vander Waals radius. But it has an atomic radius of 190pm.

Thulium ionic/covalent radius

The ionic radius of thulium is 0. 869Ao.The covalent radius of 1.759Ao.

Thulium isotopes

Isotopes are two or more forms which are having same atomic number but different atomic mass. Let us find the isotopes of thulium.

Thulium has 35 isotopes that are from 145Tm to 179Tm. Following are the stable isotopes of thulium.

Thulium isotopesAtomic numberAtomic MassIsotopic MassHalf-lifeDecay modeDaughter Isotopes
167Tm6998166.9328516(29)9.25(2) dEC167Er
168Tm6999167.934173(3)93.1(2) dβ+ (99.99%)168Er
170Tm69101169.9358014(27)128.6(3) dβ (99.86%)
171Tm69102170.9364294(28)4.12(13) μsβ171Yb
Isotopes of thulium

Thulium electronic shell

The electrons present in the element represent the electronic shell around the nucleus of that element. Let us see the electronic shell of thulium.

The electronic shell of thulium includes s, p, d, and f shells. Tm has electronic distribution as 2,8,18,31,8,2.

Thulium energy of first ionization

The first ionization energy of thulium is 596.70 KJ/mol-1. This much energy is required to remove electrons from the 4f valence shell of thulium.

Thulium energy of second ionization

The second ionization energy of thulium 1162.66 KJ/mol-1

Thulium energy of third ionization

The third ionization energy of thulium is 2284.79 KJ/mol-1.

Thulium oxidation states

Thulium shows a +3-oxidation state. Because thulium loses 3 electrons from its valence electrons.

Thulium electronic configurations

Thulium shows the following electronic configuration. It has a total 69 electrons

[Xe] 4f13 6s2

Thulium CAS number

The CAS number of thulium is 7440-30-4.

Thulium Chem Spider ID

The ChemSpider ID of thulium is 22400.

Thulium allotropic forms

Allotropes are one or more forms that all have different physical forms of the same element. Let us determine the allotropes of thulium.

Thulium has two allotropes tetragonal α-Tm and stable hexagonal β-Tm. Both allotropes have the same element but may have different physical forms.

Thulium chemical classification

The chemical classification of thulium is as follows.

  • Thulium is expensive least abundant rare earth metal.
  • Thulium is a reactive metal.
  • Thulium pure form is silvery lustre, and it is a bright metal.

Thulium state at room temperature

Thulium is solid at room temperature.

Is thulium paramagnetic?

The elements are weekly attracted by the external magnetic field then they show paramagnetic nature. Let us see whether thulium is paramagnetic or not.

Thulium is paramagnetic in nature. As it contains unpaired electrons in a 4f valence shell.


Thulium is the f-block rare earth metal. It has an unpaired electron in the 4f orbital. It is present in the lanthanides group and the 6th period of the periodic table. It has different isotopes from 145Tm to 179Tm. Also, thulium is paramagnetic in nature.