Osmium

Osmium is the densest naturally occurring element, a cubic centimetre of it weighs 22.59 grams, twice as much as lead. It was once used in the tips of fountain pen nibs and the points of gramophone styluses, where its extreme hardness prevented wear. Today it is used in specialised high-durability alloys and some chemical catalysts.

• Atomic Number7676 protons, 76 electrons
• Atomic Mass190.2 u76× heavier than hydrogen
• State at Room TempSolidSolid
• Density22.57 g/cm³
• Melting / Boiling3032.8°C / 5011.9°C
• Discovered1803

What is Osmium?

Osmium is a brittle, blue-white platinum group metal in Group 8. With 76 protons and a density of 22.59 g/cm³, it edges out iridium for the title of densest element. Osmium tetroxide (OsO₄) is extremely toxic and volatile. Named from the Greek osme meaning smell, its tetroxide has a sharp, acrid odour.

Discovered in 1803 by Smithson Tennant in London, in the residue left after dissolving platinum in aqua regia: the same residue that yielded iridium.

Fact Osmium tetroxide (OsO₄) is one of the most toxic industrial chemicals used in science. It stains and permanently damages the cornea of the eye at concentrations too low to smell. Yet it is indispensable in biological electron microscopy, where its affinity for lipid membranes makes cell structures visible at nanometre resolution.

Where you find Osmium

On Earth

By-product of platinum group metal mining. South Africa and Russia are primary sources.

How we use Osmium

• High-wear alloy tips for fountain pen nibs and electrical contacts.. Pen nibs and contacts
• Osmium tetroxide is used as a biological stain in electron microscopy, where its heavy atoms provide contrast for imaging cell structures.. Electron microscopy
• H. a
• P. r

Did you know? Osmium tetroxide (OsO₄) is one of the most toxic industrial chemicals used in science. It stains and permanently damages the cornea of the eye at concentrations too low to smell. Yet it is indispensable in biological electron microscopy, where its affinity for lipid membranes makes cell structures visible at nanometre resolution.

How it was discovered

Discovered in 1803 by Smithson Tennant in London, in the residue left after dissolving platinum in aqua regia: the same residue that yielded iridium.

Deeper dive: osmium properties and applications

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Moving to 77 protons on the periodic table takes us to the next element.