Editing Erbium (section)

===Chemical properties===
Erbium metal retains its luster in dry air, however will tarnish slowly in moist air and burns readily to form [[erbium(III) oxide]]:<ref name="emsley" />
:4 Er + 3 O<sub>2</sub> → 2 Er<sub>2</sub>O<sub>3</sub>

Erbium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form [[erbium hydroxide]]:<ref>{{cite journal | url=https://iopscience.iop.org/article/10.1088/0957-4484/19/18/185606/meta | doi=10.1088/0957-4484/19/18/185606 | title=Synthesis of erbium hydroxide microflowers and nanostructures in subcritical water | year=2008 | last1=Assaaoudi | first1=H. | last2=Fang | first2=Z. | last3=Butler | first3=I. S. | last4=Kozinski | first4=J. A. | journal=Nanotechnology | volume=19 | issue=18 | page=185606 | pmid=21825694 | bibcode=2008Nanot..19r5606A | s2cid=24755693 | url-access=subscription }}</ref>
:2 Er (s) + 6 H<sub>2</sub>O (l) → 2 Er(OH)<sub>3</sub> (aq) + 3 H<sub>2</sub> (g)

Erbium metal reacts with all the halogens:<ref name="Webelements" />
:2 Er (s) + 3 F<sub>2</sub> (g) → 2 ErF<sub>3</sub> (s) [pink]
:2 Er (s) + 3 Cl<sub>2</sub> (g) → 2 ErCl<sub>3</sub> (s) [violet]
:2 Er (s) + 3 Br<sub>2</sub> (g) → 2 ErBr<sub>3</sub> (s) [violet]
:2 Er (s) + 3 I<sub>2</sub> (g) → 2 ErI<sub>3</sub> (s) [violet]

Erbium dissolves readily in dilute [[sulfuric acid]] to form solutions containing hydrated Er(III) ions, which exist as rose red [Er(OH<sub>2</sub>)<sub>9</sub>]<sup>3+</sup> hydration complexes:<ref name="Webelements">{{cite web| url =https://www.webelements.com/erbium/chemistry.html| title =Chemical reactions of Erbium| publisher=Webelements| access-date=2009-06-06}}</ref>

:2 Er (s) + 3 H<sub>2</sub>SO<sub>4</sub> (aq) → 2 Er<sup>3+</sup> (aq) + 3 {{chem|SO|4|2-}} (aq) + 3 H<sub>2</sub> (g)