Transition metalElement 76 · d-block

Osmium (Os)

Osmium (Os) is a transition metal with atomic number 76 and a standard atomic weight of 190.23. At room temperature it is a solid that melts at 3,033 °C and boils at 5,008 °C.

76OsOsmium190.23

Atomic number

protons

Atomic weight

190.23

CIAAW 2024

Melting point

3,033 °C

3,306.15 K

Boiling point

5,008 °C

5,281.15 K

Density

22.587 g/cm³

near room temperature

Electronegativity

2.2

Pauling scale

State at 25 °C

Solid

Discovered

1803

England

Osmium at a glance

Identity

Symbol	Os
Atomic number (Z)	76
Atomic weight	190.23 ± 0.03 (CIAAW 2024)
Category	Transition metal
Group	8
Period	6
Block	d-block
CAS number	7440-04-2

Atomic properties

Electron configuration	[Xe] 4f¹⁴ 5d⁶ 6s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁶ 6s²
Electrons per shell	2, 8, 18, 32, 14, 2
Oxidation states	+4 Less common: -4, -2, -1, 0, +1, +2, +3, +5, +6, +7, +8
Electronegativity (Pauling)	2.2
First ionisation energy	8.438 eV (814.2 kJ/mol) 2nd: 17 eV · 3rd: 25 eV
Electron affinity	1.1 eV
Atomic radius (empirical)	130 pm
Covalent radius	129 pm
Van der Waals radius	216 pm

Physical properties

State at 25 °C	Solid
Melting point	3,033 °C · 5,491.4 °F · 3,306.15 K
Boiling point	5,008 °C · 9,046.4 °F · 5,281.15 K
Density	22.5872 g/cm³
Specific heat capacity	0.13 J/(g·K)
Crystal structure	Hexagonal

Isotopes & abundance

Natural occurrence	Primordial
Radioactive	No
Natural isotopes (abundance)	¹⁹²Os 40.78%, ¹⁹⁰Os 26.26%, ¹⁸⁹Os 16.15%, ¹⁸⁸Os 13.24%, ¹⁸⁷Os 1.96%, ¹⁸⁶Os 1.59% (radioactive)
Stable isotopes	5
Known isotopes	43
Abundance in Earth's crust	0.0015 mg/kg

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Osmium electron configuration

Osmium has 76 electrons. Written in short form, its ground-state configuration is [Xe] 4f¹⁴ 5d⁶ 6s² — the electrons of the noble gas xenon, plus 4f¹⁴ 5d⁶ 6s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁶ 6s².

4f↑↓↑↓↑↓↑↓↑↓↑↓↑↓

5d↑↓↑↑↑↑

6s↑↓

Discovery and name

Discovered

1803 — Smithson Tennant · England.

Name

Greek osmē, smell — for its pungent oxide.

Known for

The densest naturally occurring element (22.59 g/cm³). Used in hard alloys for pen nibs, electrical contacts and instrument pivots.

Isotopes of osmium

Naturally occurring osmium is a mix of 7 isotopes. Each has 76 protons; they differ in the number of neutrons:

Isotope	Protons	Neutrons	Natural abundance	Stability
¹⁹²Os	76	116	40.78%	stable
¹⁹⁰Os	76	114	26.26%	stable
¹⁸⁹Os	76	113	16.15%	stable
¹⁸⁸Os	76	112	13.24%	stable
¹⁸⁷Os	76	111	1.96%	stable
¹⁸⁶Os	76	110	1.59%	radioactive · half-life 2 × 10¹⁵ years
¹⁸⁴Os	76	108	0.02%	radioactive · half-life 11.2 trillion years

43 isotopes of osmium are known in our data set (half-lives as published in nuclear data tables).

Osmium compared with group 8

The other elements in group 8, from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Iron	26	55.845	1,538 °C	2,861 °C	7.87 g/cm³	1.83
Ruthenium	44	101.07	2,333 °C	4,147 °C	12.1 g/cm³	2.2
Osmium	76	190.23	3,033 °C	5,008 °C	22.587 g/cm³	2.2
Hassium	108	[269]	—	—	40.7 g/cm³ (pred.)	—

Frequently asked questions

6 answers

What is the atomic mass of osmium?

The standard atomic weight of osmium is 190.23 ± 0.03 (CIAAW 2024), so one mole weighs about 190.23 grams.

How many protons, neutrons and electrons does osmium have?

A neutral osmium atom has 76 protons and 76 electrons. Its most common isotope, osmium-192, has 116 neutrons.

What is the electron configuration of osmium?

[Xe] 4f¹⁴ 5d⁶ 6s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁶ 6s²).

What are the melting and boiling points of osmium?

Osmium melts at 3,033 °C (5,491.4 °F) and boils at 5,008 °C (9,046.4 °F).

Is osmium a metal?

Osmium is a metal. It is in group 8, period 6, and is a solid at room temperature.

Who discovered osmium?

1803 — Smithson Tennant (England).