Chemical element · reference page

76Os

Osmium

Osmium is element 76 (Os), located in period 6, group 8 and the d block. At room temperature its reference phase is solid. Its electron configuration is [Xe] 4f14 5d6 6s2.

Atomic number76

Standard atomic weight190.23(3)

Group8

Period6

Blockd

Electron configuration[Xe] 4f14 5d6 6s2

Electronic structure

What controls its chemistry

The d subshell participates in the chemistry of osmium. Transition metals can use electrons of similar energies in bonding, which is why variable oxidation states, coordination compounds and catalytic behaviour are common across the d block.

Its electron configuration, [Xe] 4f14 5d6 6s2, should be read together with the oxidation state of the compound: removing electrons changes which d orbitals are occupied and can alter colour, magnetism, bonding and reactivity.

Chemical forms

Compounds, ions and materials

For osmium, important chemical forms include metals and alloys, oxides, halides and coordination compounds. Variable oxidation states are common because s and d electrons have similar energies, and ligands around the metal ion can strongly alter colour, magnetism and reactivity.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 22.59 g/cm³. The melting point is 3 328 K (3 055 °C). The boiling point is 5 285 K (5 012 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where osmium is found and used

In practice, osmium is encountered in alloys, catalysts and fountain pen.

In practice

Examples of real uses

Alloys

Osmium is added to metals to change strength, corrosion resistance, melting behaviour or high-temperature performance.

Catalysts

Osmium is used to accelerate chemical reactions without being consumed in the overall reaction.

Fountain pen

Osmium-containing hard, wear-resistant alloys have been used in fine instrument tips and other small components exposed to repeated friction.

Periodic position

What its neighbours tell us

Osmium is in period 6 and group 8. In the neighbourhood shown here, it lies between rhenium and iridium in the same period; ruthenium is above it and hassium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationtransition metal

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 32 · 14 · 2

Density22.59 g/cm³

Melting point3 328 K (3 055 °C)

Boiling point5 285 K (5 012 °C)

Pauling electronegativity2.2

First ionisation energy814kJ/mol

Electron affinity104 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of osmium is associated with Smithson Tennant. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 190.23(3). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Osmium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with osmium depend on chemical form, dose and route of exposure. Pure osmium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.