Transition metalElement 77 · d-block

Iridium (Ir)

Iridium (Ir) is a transition metal with atomic number 77 and a standard atomic weight of 192.22. At room temperature it is a solid that melts at 2,446 °C and boils at 4,428 °C.

77IrIridium192.22

Atomic number

protons

Atomic weight

192.22

CIAAW 2024

Melting point

2,446 °C

2,719.15 K

Boiling point

4,428 °C

4,701.15 K

Density

22.562 g/cm³

near room temperature

Electronegativity

2.2

Pauling scale

State at 25 °C

Solid

Discovered

1803

England

Iridium at a glance

Identity

Symbol	Ir
Atomic number (Z)	77
Atomic weight	192.22 ± 0.01 (CIAAW 2024)
Category	Transition metal
Group	9
Period	6
Block	d-block
CAS number	7439-88-5

Atomic properties

Electron configuration	[Xe] 4f¹⁴ 5d⁷ 6s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁷ 6s²
Electrons per shell	2, 8, 18, 32, 15, 2
Oxidation states	+3, +4 Less common: -3, -2, -1, +1, +2, +5, +6, +7, +8, +9
Electronegativity (Pauling)	2.2
First ionisation energy	8.967 eV (865.2 kJ/mol) 2nd: 17 eV · 3rd: 28 eV
Electron affinity	1.564 eV
Atomic radius (empirical)	135 pm
Covalent radius	122 pm
Van der Waals radius	213 pm

Physical properties

State at 25 °C	Solid
Melting point	2,446 °C · 4,434.8 °F · 2,719.15 K
Boiling point	4,428 °C · 8,002.4 °F · 4,701.15 K
Density	22.5622 g/cm³
Specific heat capacity	0.131 J/(g·K)
Thermal conductivity	147 W/(m·K)
Crystal structure	Face-centred cubic

Isotopes & abundance

Natural occurrence	Primordial
Radioactive	No
Natural isotopes (abundance)	¹⁹³Ir 62.7%, ¹⁹¹Ir 37.3%
Stable isotopes	3
Known isotopes	43
Abundance in Earth's crust	0.001 mg/kg

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

Iridium electron configuration

Iridium has 77 electrons. Written in short form, its ground-state configuration is [Xe] 4f¹⁴ 5d⁷ 6s² — the electrons of the noble gas xenon, plus 4f¹⁴ 5d⁷ 6s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁷ 6s².

4f↑↓↑↓↑↓↑↓↑↓↑↓↑↓

5d↑↓↑↓↑↑↑

6s↑↓

Discovery and name

Discovered

1803 — Smithson Tennant · England.

Name

Iris, Greek goddess of the rainbow — for its colourful salts.

Known for

The most corrosion-resistant metal and among the densest. The 1889 international prototype kilogram was 10% iridium; used in spark plugs.

Isotopes of iridium

Naturally occurring iridium is a mix of 2 isotopes. Each has 77 protons; they differ in the number of neutrons:

Isotope	Protons	Neutrons	Natural abundance	Stability
¹⁹³Ir	77	116	62.7%	stable
¹⁹¹Ir	77	114	37.3%	stable

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

Iridium compared with group 9

The other elements in group 9, from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Cobalt	27	58.933	1,495 °C	2,927 °C	8.86 g/cm³	1.88
Rhodium	45	102.91	1,963 °C	3,695 °C	12.4 g/cm³	2.28
Iridium	77	192.22	2,446 °C	4,428 °C	22.562 g/cm³	2.2
Meitnerium	109	[278]	—	—	37.4 g/cm³ (pred.)	—

Frequently asked questions

6 answers

What is the atomic mass of iridium?

The standard atomic weight of iridium is 192.22 ± 0.01 (CIAAW 2024), so one mole weighs about 192.22 grams.

How many protons, neutrons and electrons does iridium have?

A neutral iridium atom has 77 protons and 77 electrons. Its most common isotope, iridium-193, has 116 neutrons.

What is the electron configuration of iridium?

[Xe] 4f¹⁴ 5d⁷ 6s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁷ 6s²).

What are the melting and boiling points of iridium?

Iridium melts at 2,446 °C (4,434.8 °F) and boils at 4,428 °C (8,002.4 °F).

Is iridium a metal?

Iridium is a metal. It is in group 9, period 6, and is a solid at room temperature.

Who discovered iridium?

1803 — Smithson Tennant (England).