Thulium

Thulium dissolves readily in dilute sulphuric acid, forming a pale green solution of Tm(III) ions and hydrogen gas, H₂.

2 Tm(s) + 3 H₂SO₄(aq) 2 Tm³⁺(aq) + 3 SO₄²⁻(aq) + 3 H₂(g)

Thulium tarnishes slowly in air and burns readily, forming thulium(III) oxide, Tm₂O₃.
4 Tm(s) + 3 O₂(g) 2 Tm₂O₃(s)

Thulium reacts with the halogens, forming the corresponding thulium(III) halides:

2 Tm(s) + 3 F₂(g) 2 TmF₃(s) [white]
2 Tm(s) + 3 Cl₂(g) 2 TmCl₃(s) [yellow]
2 Tm(s) + 3 Br₂(g) 2 TmBr₃(s) [white]
2 Tm(s) + 3 I₂(g) 2 TmI₃(s) [yellow]

Thulium reacts slowly with cold water, and quickly with hot water, forming thulium(III) hydroxide, Tm(OH)₃, and hydrogen gas, H₂

2 Tm(s) + 6 H₂O(l) 2 Tm(OH)₃(aq) + 3 H₂(g)