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Information valid for Tm-169 unless otherwise noted

Basic Information

Symbol: Tm
Atomic Number: 69
Mass: 168.9342
Melting Point: 1545.0 C
Boiling Point: 1727.0 C
Number of Protons/Electrons: 69
Number of Neutrons: 100
Classification: Rare Earth
Crystal Structure: Hexagonal
Density @ 293 K: 9.321 g/cm3
Color: silverish

Atomic Structure

[Bohr Model of Thulium]
Number of Energy Levels: 6

  1. First Energy Level: 2
    Second Energy Level: 8
    Third Energy Level: 18
    Fourth Energy Level: 31
    Fifth Energy Level: 8
    Sixth Energy Level: 2


Isotope Half Life
Tm-168 93.1 days
Tm-169 Stable
Tm-170 128.6 days
Tm-171 1.92 years
Tm-172 2.65 days


Date of Discovery: 1879
Discoverer: Per Theodor Cleve
Name Origin: From Thule (ancient name of Scandinavia)
Uses: power for portable x-ray machines
Obtained From: gadolinite, euxenite, xenotime