Periodic Table


Atomic number: 69
Atomic weight: 168.93421
Symbol: Tm
Group number: (lanthanide)
Electronic configuration: [Xe].4f13.6s2


Thulium is the least abundant of the earth elements, and is about as rare as silver, gold, or cadmium.

The pure metal has a bright, silvery lustre. It is reasonably stable in air, but the metal must be protected from moisture. The element is silvery-grey, soft, malleable, and ductile, and can be cut with a knife. It is a rare earth metal found in minerals such as monazite.

General information

Discoveror: Per Theodore Cleve
Date discovered: 1879
Discovered at: Sweden
Meaning of name: Named after ""Thule", an ancient name for Scandinavia

Physical data

Standard state: solid at 298 K
Colour: silvery white
Density of solid at ambient temperature/kg m-3: 9321
Molar volume/cm3: 19.1

Radii /pm

Atomic: 222
Covalent (single bond):
Pauling radius for the ion [Tm]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius201.1no datano data26.1


Both values are quoted on the Pauling scale.

Pauling: 1.25
Allred Rochow: 1.11

Crystal Structure

structure: hcp (hexagonal close-packed)

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 1818
boiling point: 2223

Enthalpies /kJ mol-1

fusion: 16.8
vaporization: 247

single bond enthalpies:
Tm-F Tm-Cl Tm-Br Tm-I Tm-Tm
no data no data no data 251 no data

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
169Tm168.934212 (4)100

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/Tm.html