Thulium

Chaitra 26/06/2026 19:58:08 Updated 26/06/2026 19:58:08

Property	Value
Atomic Number	69
Element	Thulium
Symbol	Tm
Atomic Mass	168.934 u
Number of Neutrons	100 (most common isotope, Thulium-169)
Number of Protons	69
Number of Electrons	69
Period	6
Group	Lanthanide (no fixed group number)
Phase	Solid
Radioactive	No
Natural	Yes
Metal	Yes
Nonmetal	No
Metalloid	No
Type	Lanthanide
Atomic Radius	222 pm
Electronegativity	1.25 (Pauling scale)
First Ionization Energy	6.184 eV
Density	9.32 g/cm³
Melting Point	1545 °C
Boiling Point	1950 °C
Number of Isotopes	1 stable (Thulium-169)
Discoverer	Per Teodor Cleve
Year	1879
Specific Heat	0.160 J/g·K
Number of Shells	6
Number of Valence Electrons	3