Editing Hafnium (section)

===Chemical characteristics===
{{See also|Hafnium#Chemical compounds|label1=&sect;&nbsp;Chemical compounds}}
[[File:Hafnium(IV) oxide.jpg|thumb|left|[[Hafnium(IV) oxide|Hafnium dioxide]] (HfO<sub>2</sub>)]]
Hafnium reacts in air to form a [[Passivation (chemistry)|protective film]] that inhibits further [[corrosion]].  Despite this, the metal is attacked by hydrofluoric acid and concentrated sulfuric acid, and can be oxidized with [[halogen]]s or burnt in air.  Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air. The metal is resistant to concentrated [[alkali]]s.

As a consequence of [[lanthanide contraction]], the chemistry of hafnium and zirconium is so similar that the two cannot be separated based on differing chemical reactions. The melting and boiling points of the compounds and the [[solubility]] in solvents are the major differences in the chemistry of these twin elements.<ref name="Holl">{{cite book|publisher = [[Walter de Gruyter]]|date = 1985|edition = 91–100|pages=1056–1057|isbn = 978-3-11-007511-3|title = Lehrbuch der Anorganischen Chemie|first = Arnold F.|last = Holleman |author2 = Wiberg, Egon |author3=Wiberg, Nils |language = de|doi=10.1515/9783110206845|author-link2=Egon Wiberg}}</ref>