Osmium commonly forms Os3+ Os4+ in introductory ionic compounds.
| Element | Osmium |
|---|---|
| Symbol | Os |
| Atomic number | 76 |
| Common ionic charge | +3, +4 |
| Common ions | Os3+, Os4+ |
Images are used as visual references; charge rules still depend on the compound.
Osmium is [Xe]4f14 5d6 6s2. Group 8's heaviest member can engage all eight valence electrons — the +8 of OsO4 is the highest oxidation state routinely met in a bottle (only ruthenium and xenon match it). Relativistic stabilization of its lower orbitals makes this extreme reachable.
This is a classroom reference range, not an exhaustive list of all oxidation states.
Handling 'the noble metal osmium' casually. The metal is noble; its dust is not — finely divided osmium slowly forms OsO4 in plain air. The +8 oxide's 'smell' gave the element its name (osme, Greek for odor). Museum-grade caution applies.
Four O at -2 give Os = +8. Lipid double bonds reduce it to black OsO2 (+4), simultaneously staining membranes and stitching them rigid — contrast and fixation from one charge drop of four units.
Osmium chloride
Os3+ balances chloride ions.
Osmium oxide
Osmium can form oxides where total positive and negative charge balances.
No — 22.59 g/cm³ comes from relativistically contracted orbitals packing neutral atoms tightly. The same relativistic physics does, separately, help its high charge states exist.
Early lightbulb filaments (the 'Os' in Osram) used the neutral metal; fountain-pen tips still use osmium-iridium alloy. Its ionic chemistry stays mostly in research and microscopy labs.
Both are +8 tetroxides, but ruthenium's is fiercer and less selective; osmium's is stable enough to sell in ampoules. Descending a group tames the top charge — the Re/Mn story repeated one column over.
Combine positive and negative ions so the total charge is zero — or let the ionic compound calculator do the crossing for you. The full chart lives on the periodic table with charges.
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