Chemical reactions of the elements
Reaction of osmium with air
Osmium is largely immune to atmospheric attack. On heating with oxygen, osmium metal gives the rather volatile (melting point 30°C, boiling point 130°C) osmium (VIII) oxide, OsO4. Apparently, in air, finely divided osmium metal gives off a characteristic smell of OsO4 - bad news given that OsO4 is highly toxic.
Os(s) + 2O2(g) → OsO4(s)
Normally second and third row d-block elements show similar chemistries, but in this case, ruthenium (immediately above osmium in the periodic table) burns to give ruthenium (IV) oxide, RuO2.
Reaction of osmium with water
Osmium does not react with water under normal conditions.
Reaction of osmium with the halogens
Osmium reacts with excess of fluorine, F2, at 600°C and 400 atmosphere pressure to form osmium(VII) fluoride, OsF7.
2Os(s) + 7F2(g) → 2OsF7(s) (yellow)
Under milder conditions, the hexafluoride OsF6 is produced.
Os(s) + 3F2(g) → OsF6(s) (yellow)
Osmium reacts with either chlorine, Cl2, or bromine, Br2, with heating under pressure to form the tetrahalides osmium(IV) chloride, OsCl4, or osmium(IV) bromide, OsBr4.
Os(s) + 2Cl2(g) → OsCl4(s) (red)
Os(s) + 2Br2(l) → OsBr4(s) (black)
Reaction of osmium with acids
Reaction of osmium with bases