Thulium

Element 69 · Lanthanide

Specimen

Atomic number: 69
Atomic mass: 168.934
State at room temperature: Solid
Melting point: 1,545 °C
Boiling point: 1,950 °C
Density: 9.32 g/cm³
Discovered: 1879

Physical data from PubChem.¹

Can I eat it?

In food and water: Not needed, little harm known. Thulium has no known function in the body. The RSC calls it non-toxic. In rats, half died only at 6.25 g of thulium chloride per kg of body weight. There are few studies of it in food. ²³

The atom

Shell	Electrons
1 (K)	2
2 (L)	8
3 (M)	18
4 (N)	31
5 (O)	8
6 (P) outermost	2
Total	69

Configuration [Xe] 4f¹³ 6s²

4f ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑

6s ↑ ↓

A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 69 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Xe core, with one arrow per electron.

Related elements

Sources

1

National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

Atomic mass, electron configuration, melting and boiling points, density and discovery year for all 118 elements.
2
Royal Society of Chemistry, 2026. Thulium - Element information, properties and uses .
- Thulium has no known biological role. It is non-toxic.
3
Toxicology Excellence for Risk Assessment (TERA), for the US Bureau of Land Management, 1999. Development of Reference Doses and Reference Concentrations for Lanthanides , Section 2.4 (oral toxicity data in experimental animals).
- 6250 mg/kg for thulium chloride

Specimen

Can I eat it?

The atom

Related elements

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Sources