Osmium (Os)


Osmium is a chemical element with the atomic number 76 in the periodic table. It’s one of the rarest chemical elements that occur in Earth’s crust, with 1.5×10-3 ppm of natural abundance. 

Being a member of the platinum group metals (PGM), this noble metal with a pungent odor and high toxicity has many applications in medicine and various industries. As a part of the platinum metals group, osmium is often alloyed with the other precious metals. In this way, osmium alloys are used for an added durability, firmness, and anti-corrosive protection of manufactured items. 

Fact Box

Chemical and Physical Properties of Osmium

The symbol in the periodic table of elements: Os

Atomic number: 76

Atomic weight (mass): 190.2 g.mol-1

Group number: 8 (PGM)

Period: 6 (d-block)

Color: A bluish-white color with a silvery luster

Physical state: Solid at room temperature

Half-life: From 0.64(6) milliseconds to 2.0(11)×1015 years

Electronegativity according to Pauling: 2.2

Density: 22.5 g.cm-3 at 20°C

Melting point: 3033°C, 5491°F, 3306 K

Boiling point: 5008°C, 9046°F, 5281 K

Van der Waals radius: 0.136 nm

Ionic radius: 0.067 nm (+4)

Isotopes: 37

Most characteristic isotope: 192Os

Electronic shell: [Xe] 4f14 5d 6s2

The energy of the first ionization: 838 kJ.mol-1

The energy of the second ionization: N/A

Discovery date: In 1803 by Smithson Tennant and William Hyde Wollaston

With the periodic table symbol Os, atomic number 76, atomic mass of 190.2 g.mol-1, and electron configuration [Xe] 4f14 5d6s2, osmium is a hard and brittle bluish-white metal with a silvery lustre and pungent odor.

Osmium reaches its boiling point at 5008°C, 9046°F, 5281 K, while the melting point is achieved at 3033°C, 5491°F, 3306 K. In this regard, this chemical element has one of the highest melting and boiling points. 

This member of the platinum metals family of elements has an electronegativity of 2.2 according to Pauling, whereas the atomic radius according to van der Waals is 0.136 nm. Osmium metal has an excellent anti-corrosive property, and is resistant to wear and tear. Even after exposure to high temperatures, osmium does not lose its silvery luster.

How Was Osmium Discovered?

Osmium was discovered by the English chemists Smithson Tennant and William Hyde Wollaston in 1803. At that time, some scientists believed that crude platinum powder was actually graphite (C), archaically known as plumbago. However, Tennant’s and Wollaston’s curiosity spurred them to conduct additional experiments to obtain more valid evidence on this claim. 

These two discoverers then decided to implement the method for the isolation of palladium and rhodium out of platinum ore that had been conceptualized by Wollaston. Namely, Tennant and Wollaston tried to dissolve a sample of crude platinum in aqua regia (a mixture of hydrochloric acid and nitric acid) in a London laboratory. 

This experiment resulted in a metallic black powder. But, the English chemists were still convinced that there’s something more to this graphite-resembling substance. So, they attempted mixing the powder with sodium hydroxide after which they heated the mixture. By adding water to the residue, the alkali was removed and mixed with hydrochloric acid. 

This step of the experiment proved to be revolutionary because Tennant and Wollaston discovered an unknown metal element exactly in this solution. From the new element referred to as ‘ptene’, they succeeded in isolating a substance with an extremely strong smell – osmium tetroxide (OsO4). 

How Did Osmium Get Its Name?

As a result of its exceptionally strong and unpleasant smell, element 76 was given the name ‘osmium’. The term is derived from the Greek word  ‘osme‘, which means ‘smelly’.

Where Can You Find Osmium?

Osmium is the rarest and least abundant transition metal that naturally occurs in Earth’s crust. It’s mainly traced in alloys together with other platinum metals. Furthermore, element 76 is also traced in the mineral osmiridium (also known as iridosmine – an alloy of osmium and iridium). Osmiridium deposits are most often found in the gold-bearing conglomerates located in the Ural Mountains (Russia), Witwatersrand (South Africa), and California and Oregon (United States). 

This toxic chemical element can also be found in the minerals siserskite, aurosmiridium, as well as in native platinum ores. For commercial purposes, osmium is mostly obtained as a byproduct of nickel refining, i.e. from the processing of platinum and nickel ores.

Osmium in Everyday Life

As a member of the platinum metals group, the main application of this transition metal is in the making of very hard alloys that characterize with great resistance to wear. Osmium can be also applied in the following instances:

  • In medicine, osmium is used for making surgical implants, such as pacemakers and replacement heart valves;
  • Due to its toughness and resistance to wear, osmium is used in the manufacturing of fountain pen tips and phonograph needles, instrument pivots, electrical contacts, and compass needles;
  • Osmium tetroxide is often used as a fingerprint detection chemical, as well as in microscopy as a stain for fatty tissue;
  • Synovectomy is a technique in medicine used for treatment of arthritis in which osmium is applied;
  • In transmission electron microscopy (TEM), osmium is used as an intensifier of the image contrast;
  • Together with iridium and rhenium, the 188Os isotope is applied in the dating of both terrestrial and meteoric rocks. 

How Dangerous Is Osmium?

Osmium tetroxide (OsO4) is considered as a highly toxic compound that may cause severe health problems, such as lung decongestion, eye irritation and inflammation, as well as skin damage. 

Upon inhalation of osmium fumes or metal dust particles, the following symptoms of osmium toxicity are typically  experienced:


  • Severe headaches;
  • Loss of breath and difficulty breathing;
  • Wheezing;
  • Abdominal cramps;
  • Lung oedema;
  • Kidney problems;
  • Gastrointestinal problems;
  • Eye damage;
  • Blurred vision;
  • Loss of vision;
  • Skin burn and discoloration;
  • Shock or collapse;
  • Death.

Environmental Effects of Osmium

Osmium tetroxide is the main source of element 76 in the environment. It forms due to the fact that some compounds of this toxic chemical element are converted to tetroxide upon their exposure to air. For this reason, this osmium compound is referred to as an airborne toxin. 

Isotopes of Osmium

Naturally occurring osmium (76Os) is made up of seven isotopes:

  • 184Os (0.02% of abundance);
  • 186Os (1.6% of abundance); 
  • 187Os (2.0% of abundance);
  • 188Os (13.2% of abundance); 
  • 189Os (16.1% of abundance);
  • 190Os (26.3% of abundance);
  • 192Os (40.8% of abundance).

There are 37 observed isotopes of osmium, with atomic masses ranging from osmium-161 to osmium-197. Among them, 30 are synthetically produced radioactive isotopes. Osmium-186 is the longest living form of element 76, with a half-life of 2.0(11)×1015 years. 


[n 1]

Z N Isotopic mass (Da)

[n 2][n 3]


[n 4]



[n 5]



[n 6]

Spin and


[n 7][n 8]

Natural abundance (mole fraction)
Excitation energy Normal proportion Range of variation
161Os 76 85 0.64(6) ms α 157W
162Os 76 86 161.98443(54)# 1.87(18) ms α 158W 0+
163Os 76 87 162.98269(43)# 5.5(6) ms α 159W 7/2−#
β+, p (rare) 162W
β+ (rare) 163Re
164Os 76 88 163.97804(22) 21(1) ms α (98%) 160W 0+
β+ (2%) 164Re
165Os 76 89 164.97676(22)# 71(3) ms α (60%) 161W (7/2−)
β+ (40%) 165Re
166Os 76 90 165.972691(20) 216(9) ms α (72%) 162W 0+
β+ (28%) 166Re
167Os 76 91 166.97155(8) 810(60) ms α (67%) 163W 3/2−#
β+ (33%) 167Re
168Os 76 92 167.967804(13) 2.06(6) s β+ (51%) 168Re 0+
α (49%) 164W
169Os 76 93 168.967019(27) 3.40(9) s β+ (89%) 169Re 3/2−#
α (11%) 165W
170Os 76 94 169.963577(12) 7.46(23) s β+ (91.4%) 170Re 0+
α (8.6%) 166W
171Os 76 95 170.963185(20) 8.3(2) s β+ (98.3%) 171Re (5/2−)
α (1.7%) 167W
172Os 76 96 171.960023(16) 19.2(5) s β+ (98.9%) 172Re 0+
α (1.1%) 168W
173Os 76 97 172.959808(16) 22.4(9) s β+ (99.6%) 173Re (5/2−)
α (.4%) 169W
174Os 76 98 173.957062(12) 44(4) s β+ (99.97%) 174Re 0+
α (.024%) 170W
175Os 76 99 174.956946(15) 1.4(1) min β+ 175Re (5/2−)
176Os 76 100 175.95481(3) 3.6(5) min β+ 176Re 0+
177Os 76 101 176.954965(17) 3.0(2) min β+ 177Re 1/2−
178Os 76 102 177.953251(18) 5.0(4) min β+ 178Re 0+
179Os 76 103 178.953816(19) 6.5(3) min β+ 179Re (1/2−)
180Os 76 104 179.952379(22) 21.5(4) min β+ 180Re 0+
181Os 76 105 180.95324(3) 105(3) min β+ 181Re 1/2−
182Os 76 106 181.952110(23) 22.10(25) h EC 182Re 0+
183Os 76 107 182.95313(5) 13.0(5) h β+ 183Re 9/2+
184Os 76 108 183.9524891(14) Observationally Stable[n 9] 0+ 2(1)×10−4
185Os 76 109 184.9540423(14) 93.6(5) d EC 185Re 1/2−
186Os[n 10] 76 110 185.9538382(15) 2.0(11)×1015 y α 182W 0+ 0.0159(3)
187Os[n 11] 76 111 186.9557505(15) Observationally Stable[n 12] 1/2− 0.0196(2)
188Os[n 11] 76 112 187.9558382(15) Observationally Stable[n 13] 0+ 0.1324(8)
189Os 76 113 188.9581475(16) Observationally Stable[n 14] 3/2− 0.1615(5)
190Os 76 114 189.9584470(16) Observationally Stable[n 15] 0+ 0.2626(2)
191Os 76 115 190.9609297(16) 15.4(1) d β 191Ir 9/2−
192Os 76 116 191.9614807(27) Observationally Stable[n 16] 0+ 0.4078(19)
193Os 76 117 192.9641516(27) 30.11(1) h β 193Ir 3/2−
194Os 76 118 193.9651821(28) 6.0(2) y β 194Ir 0+
195Os 76 119 194.96813(54) 6.5 min β 195Ir 3/2−#
196Os 76 120 195.96964(4) 34.9(2) min β 196Ir 0+
197Os 76 121 2.8(6) min

Source: Wikipedia

List of Osmium Compounds 

When osmium participates in a compound, it can occur in the oxidation states of +2 to +8. However, this transition metal most commonly adopts the +2, +3, +4, and +8 oxidation states. 

Osmium forms unstable compounds with alkali elements, while it produces the highly toxic chlorine gas in reaction with hydrochloric acid. Osmium also reacts with base compounds, fluorine, and halogens. 

When osmium powder is exposed to air, osmium tetra-oxide is formed. Osmium(VIII) oxide (OsO4) is a powerful oxidizing agent and highly toxic osmium compound with a pale-yellow color. It carries the characteristic pungent smell associated with this chemical element. 

The list of most commonly prepared osmium compounds contains the following items:


  • Osmocene
  • Osmiridium
  • Osmium borides
  • Osmium dioxide
  • Osmium hexafluoride
  • Osmium pentacarbonyl
  • Osmium pentafluoride
  • Osmium tetroxide
  • Osmium(IV) chloride
  • Potassium osmate
  • Triosmium dodecacarbonyl

5 Interesting Facts and Explanations

  1. 1803 was a fruitful year for English scientists. While Smithson Tennant discovered the chemical elements osmium and iridium the same year, Wollaston also succeeded to discover two other chemicals – palladium and rhodium. 
  2. While performing his chemical experiments and studies, Tennant also became the first scientist to determine that diamonds are pure carbon
  3. Osmium is the densest naturally occurring stable chemical element on Earth. 
  4. Out of all elements that comprise the PMG – platinum metals group (ruthenium, rhodium, palladium, iridium, and platinum), osmium has the highest melting point and the lowest vapor pressure. 
  5. Element 76 has no known biological role.

Chemical Property and physical property of element Osmium

Symbol of Osmium: Os
Name: Osmium
Atomic Number of Osmium: 76
Atomic Mass of Osmium: 190.23
Uses of Osmium: Used to tip gold pen points, instrument pivots, to make electric light filaments. Used for high temp. alloys and pressure bearings. Very hard and resists corrosion better than any other.
Description of Osmium: Heavy, brittle, white metal.
Melting Point of Osmium:
Boiling Point of Osmium:
Group of Osmium: Transition Metal
Shells of Osmium: 2,8,18,32,14,2
Orbitals of Osmium: [Xe] 4f14 5d6 6s2
Valence of Osmium: 0,3,4,6,8
Crystal Structure of Osmium: Hexagonal
Electro Negativity of Osmium: 2.2
Covalent Radius of Osmium: 1.26 Å
Ionic Radius of Osmium: .63 (+4) Å
Atomic Radius of Osmium: 1.92 Å
Atomic Volume of Osmium: 08.49 cm³/mol
Name Origin of Osmium: Greek: osmê (odor).
Discovered of Osmium By: Smithson Tenant
Year: 1804
Location: England
Pronounced of Osmium: OZ-mi-em
Oxydation States of Osmium: 2,3,(4),6,8
Density of Osmium: 22.40 g/cm³