Element 69 · Lanthanide
Thulium (Tm) — Element 69
Thule — mythical north
Thulium (Tm) is a lanthanide in Period 6 (f-block) of the periodic table with atomic number 69, standard atomic weight 168.93 u, and ground-state electron configuration [Xe] 4f¹³ 6s². At standard temperature and pressure it is classified as a solid with 3 valence electrons and common oxidation states +3.
Portable X-ray devices
What are the atomic properties and physical constants of Thulium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 69
- Standard atomic mass
- 168.93 u
- Chemical family
- Lanthanide
- Ground-state configuration
- [Xe] 4f¹³ 6s²
- Electrons per shell
- 2, 8, 18, 31, 8, 2
- Valence electrons
- 3
- Common ion charges / oxidation states
- +3
- Phase at STP
- Solid
- Pauling electronegativity
- 1.25 Pauling
- First ionization energy
- 597 kJ/mol
- Atomic radius
- 222 pm
- Melting point
- 1,545 °C
- Boiling point
- 1,950 °C
- Discovery year
- 1879
- Table coordinate
- Period 6, f-block
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Thulium’s shells?
A neutral Thulium atom contains 69 electrons distributed across 6 occupied principal energy shells ([Xe] 4f¹³ 6s²). The table below compares Thulium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Tm | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 31 e⁻ | 32 e⁻ |
| n = 5 | O | 8 e⁻ | 50 e⁻ |
| n = 6 | P | 2 e⁻ | 72 e⁻ |
Frequently Asked Questions about Thulium (Tm)
What is the atomic mass and atomic number of Thulium (Tm)?
Thulium (Tm) has atomic number Z = 69 (69 protons in its nucleus) and an IUPAC standard atomic weight of 168.93 u. It sits in Period 6 in the f-block and is classified as a lanthanide.
What is the ground-state electron configuration of Thulium?
The neutral ground-state electron configuration of Thulium (Z = 69) is [Xe] 4f¹³ 6s². Across its 6 occupied principal shells (n = 1 to n = 6), the electrons per shell are 2, 8, 18, 31, 8, 2, with 3 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Thulium?
Thulium commonly forms +3 oxidation states or ion charges in compounds. Its Pauling electronegativity is 1.25 and its first ionization energy is 597 kJ/mol.
When was Thulium discovered and what is it used for?
Thulium was discovered in 1879 (Thule — mythical north). Portable X-ray devices
How does Thulium compare to neighboring elements?
Other lanthanide elements: