Osmium

Osmium (Os) is a transition metal with atomic number 76 and an atomic mass of 190.23. Its electron configuration is [Xe] 4f14 5d6 6s2.

Osmium key data

Symbol	Os
Atomic number	76
Atomic mass (standard atomic weight)	190.23
Molar mass	190.23 g/mol
Protons	76
Neutrons (most abundant isotope, osmium-192)	116
Electrons (neutral atom)	76
Category	Transition metal
Period	6
Group	8
Block	d-block
Noble gas notation	[Xe] 4f14 5d6 6s2
Full electron configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d6 6s2
Electrons per shell	2, 8, 18, 32, 14, 2

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

Measured properties of osmium

From PubChem, the US National Institutes of Health. Public domain. The first ionisation energy is the value for osmium from the NIST Atomic Spectra Database, in place of PubChem’s 8.7 eV.

Melting point	3306 K (3032.9 °C), 4th of 103 by melting point
Boiling point	5285 K (5011.9 °C), 4th of 93 by boiling point
Density	22.57 g/cm³, 1st of 96 by density
State at room temperature	Solid
Electronegativity	2.2 (Pauling), joint 17th of 95 by electronegativity
Van der Waals radius	216 pm, joint 40th of 99 by atomic radius
First ionisation energy	8.4382 eV (814.16 kJ/mol), 29th of 102 by first ionisation energy
Electron affinity	1.1 eV (106 kJ/mol), 22nd of 57 by electron affinity
Common oxidation states	+4, +3
Discovered	1803

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Osmium electron configuration

The full electron configuration of osmium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d6 6s2. With the noble-gas core collapsed it is [Xe] 4f14 5d6 6s2, and the outermost subshell is 6s2.

Bohr model of osmium (Os): a nucleus and six shells holding 2, 8, 18, 32, 14 and 2 electrons from the inside out. — Bohr model of osmium (Os). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Orbital box diagram of osmium (Os), [Xe] 4f14 5d6 6s2, with the xenon core drawn as one bar: one box per orbital, filled by Hund’s rule, showing four unpaired electrons, in 5d. — Orbital diagram of osmium (Os). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one osmium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

one atom = 190.23 / (6.02214076 × 10²³)
= 3.1588 × 10⁻²² g

Atoms in one gram

atoms per gram = 6.02214076 × 10²³ / 190.23
= 3.1657 × 10²¹ atoms

Osmium on the periodic table

Osmium is in period 6, group 8, in the d-block.

The other elements of group 8 are iron, ruthenium and hassium.