Osmium (Os)
Element 76 · Transition metal · atomic mass 190.23 u · group 8, period 6
Electron shells: 2, 8, 18, 32, 14, 2
Osmium is the densest naturally occurring element — a litre of it weighs over 22 kg. Its oxide is volatile and dangerously toxic, which is how it got its name.
A one-litre bottle of osmium would weigh about the same as a full carry-on suitcase.
- Atomic number
- 76
- Atomic mass
- 190.23 u
- Electron configuration
- [Xe] 6s² 4f¹⁴ 5d⁶
- Group · period · block
- 8 · 6 · d
- Oxidation states
- +3, +4
- Electronegativity
- 2.2 (Pauling)
- Melting point
- 3,033 °C
- Boiling point
- 5,012 °C
- Density
- 22.57 g/cm³
- State at 20 °C
- Solid
- Appearance
- Lustrous, bluish-white metal
- Discovered
- Smithson Tennant, 1803
76 protons, and 76 electrons when neutral
IUPAC standard atomic weight
Iron group
What Osmium is used for
- Extremely durable instrument pivots
- Fountain-pen nib tips
- Electron microscopy staining
- Hard platinum alloys
Atomic structure of Osmium
A neutral osmium atom has 76 protons and 76 electrons. Its most common isotope carries about 114 neutrons, which is where the mass number 190 comes from. Change the neutron count and you have a different isotope of osmium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 14, 2. In orbital notation that is [Xe] 6s² 4f¹⁴ 5d⁶. As a d-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Osmium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Osmium sits in the periodic table
The d-block. Multiple stable oxidation states give them coloured compounds, catalytic ability and the strength that makes them the working metals of industry.
Discovery and naming
Osmium was discovered by Smithson Tennant in 1803. Its name comes from Greek osme, "smell".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Osmium?
The standard atomic weight of Osmium is 190.23 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Osmium have?
Osmium has 76 protons, because the atomic number is the proton count and that is what makes an atom Osmium at all. A neutral Osmium atom has the same number of electrons, 76. The neutron count varies by isotope; the most common one has about 114, since 190 − 76 = 114.
What is the electron configuration of Osmium?
The electron configuration of Osmium is [Xe] 6s² 4f¹⁴ 5d⁶. Its electrons are arranged 2, 8, 18, 32, 14, 2 across 6 shells.
Is Osmium a metal?
Yes. Osmium is classified as a transition metal, on the metallic side of the table.
What group and period is Osmium in?
Osmium is in group 8 (the iron group), period 6, in the d-block. The group is its column and the period is its row.
What is the charge of Osmium?
Osmium most commonly forms a 4+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound. Across all its compounds it shows oxidation states of +3, +4.
What is the melting point of Osmium?
Osmium melts at 3,033 °C and boils at 5,012 °C. That puts it in the solids at everyday temperatures.
What is Osmium used for?
Extremely durable instrument pivots, Fountain-pen nib tips, Electron microscopy staining, Hard platinum alloys. Osmium is the densest naturally occurring element — a litre of it weighs over 22 kg.
Who discovered Osmium, and where does its name come from?
Osmium (Os) was discovered by Smithson Tennant in 1803. The name comes from Greek osme, "smell".