Reaction of erbium with air

Erbium metal tarnishes slowly in air and burns readily to form erbium (III) oxide, Er₂O₃.

4Er + 3O₂ → 2Er₂O₃

Reaction of erbium with water

The silvery white metal erbium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form erbium hydroxide, Er(OH)₃, and hydrogen gas (H₂).

2Er(s) + 6H₂O(g) → 2Er(OH)₃(aq) + 3H₂(g)

Reaction of erbium with the halogens

Erbium metal reacts with all the halogens to form erbium(III) halides. So, it reacts with fluorine, F₂, chlorine, Cl₂, bromine, I₂, and iodine, I₂, to form respectively erbium(III) bromide, ErF₃, erbium(III) chloride, ErCl₃, erbium(III) bromide, ErBr₃, and erbium(III) iodide, ErI₃.

2Er(s) + 3F₂(g) → 2ErF₃(s) [pink]

2Er(s) + 3Cl₂(g) → 2ErCl₃(s) [violet]

2Er(s) + 3Br₂(g) → 2ErBr₃(s) [violet]

2Er(s) + 3I₂(g) → 2ErI₃(s) [violet]

Reaction of erbium with acids

Erbium metal dissolves readily in dilute sulphuric acid to form solutions containing the yellow aquated Er(III) ion together with hydrogen gas, H₂. It is quite likely that Er³⁺(aq) exists as largely the complex ion [Er(OH₂)₉]³⁺

2Er(s) + 3H₂SO₄(aq) → 2Er³⁺(aq) + 3SO₄^2-(aq) + 3H₂(g)

Reaction of erbium with bases