Thulium is a lanthanide used in specialized lasers and radiation sources. Irradiating it can produce an isotope useful in compact X-ray equipment. It occurs in small amounts in monazite, linking the separation of rare-earth minerals to applications where the particular isotope or optical material matters.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
How does thulium’s laser role differ from the use of thulium-170 as a radiation source?
Thulium-doped glass or crystal
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Prepare a doped optical host
Thulium is incorporated into a glass or crystal gain material. The useful optical centers occupy the host rather than forming a bulk metal object.
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TmFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
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Which energy account belongs to the thulium laser case?
Atomic identity, reference properties and structure models
INTERACTIVE 3D69 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Xe] 4f13 6s2. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
Per Teodor Cleve identified thulium as an in 1879 while investigating erbium-containing rare-earth material. Its separation joined a sequence in which apparently single substances repeatedly yielded additional elements. Later applications depended on choosing a specific form: a 1956 paper investigated thulium-170 as a radiographic source. That development involved a radioactive , not a revision of the identity or behavior of ordinary stable thulium.
1879
Thulium oxide separated
Cleve distinguished thulium within rare-earth material.
1956
Radiographic source investigated
Published research examined thulium-170 for radiography.
Thulium occurs in small amounts within rare-earth such as monazite. It accompanies other lanthanides and requires separation from them before use. Natural occurrence of the element does not imply that an application isotope is mined directly: radioactive thulium sources require nuclear production in addition to chemical preparation.
Thulium is a rare-earth metal, but its optical and nuclear applications use different forms. Thulium in a host can support laser action, while thulium-170 supplies radiation through nuclear . Stable thulium-169 and radioactive thulium-170 have the same atomic number but different nuclear compositions and application behavior.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
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Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
solid
293.15 K, 101.325 kPa
Melting point in K
1818 K
at standard pressure unless noted
Boiling point in K
2223 K
101.325 kPa
Density in g/cm³
9.32 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
1.25 Pauling
Pauling scale
First ionization energy in kJ/mol
596.7 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
190 pm
single-bond covalent radius
Common oxidation states
+3
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust in mg/kg
0.52 mg/kg
upper continental crust, mass fraction
Has stable isotopes
Yesderived
Discovery year in CE
1879 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 6
Tm 1.25 Pauling · Thulium
Electronegativity across period 6. Exact values.
Cs
0.79
Ba
0.89
La
1.1
Ce
1.12
Pr
1.13
Nd
1.14
Sm
1.17
Eu
1.2
Gd
1.2
Tb
1.1
Dy
1.22
Ho
1.23
Er
1.24
Tm
1.25
Yb
1.1
Lu
1.27
Hf
1.3
Ta
1.5
W
2.36
Re
1.9
Os
2.2
Ir
2.2
Pt
2.28
Au
2.54
Hg
2
Tl
1.62
Pb
2.33
Bi
2.02
Po
2
At
2.2
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
