069Lanthanide · Group 3 · Period 6

Thulium

Thulium (Tm) is element 69, a lanthanide in the f-block — group 3, period 6. It is a solid at room temperature with 6 electron shells (2, 8, 18, 31, 8, 2) and an atomic mass of 168.934222 u.

Atomic mass: 168.9 u
Phase · STP: solid
Melting: 1818 K · 1545 °C
Boiling: 2223 K · 1950 °C
Electronegativity: 1.25
Density: 9.32 g/cm³

Photograph — Jurii, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/thulium.php

Identity

Atomic number: 69
Standard atomic weight: 168.9 u
Category: Lanthanide
Group: 3
Period: 6
Block: f-block
Oxidation states: +3

Physical properties

Melting point: 1818 K · 1545 °C
Boiling point: 2223 K · 1950 °C
Density: 9.32 g/cm³
Molar heat capacity: 27.03 J/(mol·K)
Atomic radius: 227 pm
Electron affinity: 99 kJ/mol

Atomic structure

69protons

100neutrons

69electrons

2valence e⁻

Noble-gas notation: [Xe] 4f13 6s2
Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f13
Electrons per shell: 2, 8, 18, 31, 8, 2

Periodic trends

Where Thulium ranks across all 118 elements.

Electronegativity1.25

Ionization energy596.7 kJ/mol

Electron affinity99 kJ/mol

Density9.32 g/cm³

Atomic radius227 pm

Ionization energies

Energy to remove each successive electron (kJ/mol).

596.7

1.2k

2.3k

4.1k

Successive ionization energies (kJ/mol, log scale).

Discovery

Discovered: 1879
Discovered by: Per Teodor Cleve
Named by: —
Appearance: silvery gray