Osmium Chemical Properties (25 Facts You Should Know)

Os or Osmium is the transition metal of the d block element having a partially filled 3d orbital. Let us explain about Osmium in detail.

Osmium is the heavier transition metal of 5d series and is present in the same group of iron. Osmium is a hard metal and brittle in nature. It appears bluish-white in color, which is categorized as a platinum group, as it is found in very trace amounts in the alloy form. Os is also used as a good oxidizing agent.

Like palladium powder, Os can easily absorb hydrogen gas on its surface, so it can participate in the hydrogenation reaction easily. Now we will discuss the basic chemical properties of Osmium with proper explanation in this article.

1. Osmium symbol

Symbols are used to express the element by using one or two letters of the English or Latin alphabet of the chemical name. Let us predict the atomic symbol of Osmium.

“Os” is the atomic symbol of Osmium as the name of the element starts with O letter in the English alphabet. But since, letter O is already taken for the group 16th Oxygen element, we use the first two letters of Osmium that is, “Os” instead of the first letter to distinguish the element.

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Osmium Atomic Symbol

2. Osmium group in the periodic table

Vertical lines or columns of the periodic table are referred to as a group of the periodic table. Let us predict the group of Osmium in the periodic table.

Os belongs to group 8 in the periodic table as it is placed in the 8th vertical series of the periodic table by its atomic number by Mendeleev.

3. Osmium period in the periodic table

A horizontal line or row of the periodic table where every element is placed by its last principle quantum number is called a period. Let us predict the period of osmium.

Os is placed in the 6th period as it contains more than 54 electrons, which are placed in the 5th period. Therefore, the remaining electrons are placed in the 6th period of the periodic table. It is placed next to the lanthanide series.

4. Osmium block in the periodic table

The orbital where the valence electrons of the element are present is called the block of the periodic table. Let us predict the block of osmium.

Osmium belongs to d block as the valence electrons are present in its d orbital. It contains s, p, d and f orbitals but the outermost orbital of Os is d because of 5 principle quantum number.

5. Osmium atomic number

The value of Z, known as the atomic number, is the total number of electrons. Let us find the atomic number of Osmium.

The atomic number of Osmium is 76 which means it has 76 electrons and protons because the number of protons is always equal to the number of electrons. For this reason, they become neutral due to the neutralization of equal and opposite charges.

6. Osmium Atomic Weight

The mass of the element is called weight which is measured with respect to some standard value. Let us calculate the atomic weight of Osmium.

The atomic weight of Osmium is 190 on 12C scale, which means the atomic weight of osmium is 190/12th part. But the actual value is 190.23, which is the average value of different isotopes of Osmium.

7. Osmium Electronegativity according to Pauling

Pauling electronegativity is the power to attract any other element for that particular atom. Let us predict the electronegativity of Osmium.

The Pauling electronegativity is 2.2 for Os, which means it is close to electronegative and less electropositive as its value is greater than 1. So, it has a higher ability to attract any other element like other transition elements and form highly positively charged cations.

8. Osmium atomic Density

The number of atoms present per unit volume is called the atomic density of that respective element. Let us calculate the atomic density of Osmium.

The atomic density of Osmium is 22.5872 g/cm3 which means the weight of atoms per unit volume of Os is calculated to be 22.58. The atomic weight is divided by the standard volume value of the element by Avagardo’s value of 22.4 L at STP.

  • Atomic density = atomic mass / atomic volume
  • The atomic mass or weight of Osmium atom is 44.95 g which is established
  • The volume of Osmium molecule is 22.4 liter at STP as per Avogardo’s calculation 
  • So, the atomic density of Osmium is, 190.23/(8.42) = 22.58  g/cm3

9. Osmium melting point

Changing to a liquid state from its solid state at a particular temperature is called the melting point of an element. Let us find the melting point of Osmium.

The melting point of Osmium is 30330 C or 3306K temperature because Os has a hexagonal close-packed lattice in the crystal form when it exists in a solid state and needs greater energy to break that crystal.

10. Osmium boiling point

Boiling point is that point when the vapor pressure of an element becomes equal to its atmospheric pressure. Let us find the boiling point of Osmium.

The boiling point of Osmium is 50270 C or 5300K because it has a higher melting point, so it needs more energy than the melting point for boiling.

11. Osmium Van der Waals radius

Van der Waal’s radius is the distance between the center of two atomic spheres attached together. Let us find van der Waal’s radius of Osmium.

The Van der Waal’s radius of Os is 200 pm as it contains 5d and 4f orbitals. It also has a shielding effect on the nucleus to the outermost electrons and the radius will decrease because 5d and 4f orbital are subject to poor shielding effect.

  • Van der Waal’s radius is calculated by the mathematical formula considering the distance between two atoms, where atoms are spherical in shape.
  • Van der Waal’s radius is, Rv = dA-A / 2
  • Where RV stands for Van Waal’s radius of the molecule of spherical shape
  • dA-A is the distance between two adjacent spheres of the atomic molecule or summation of sue radius of two atomic

12. Osmium ionic radius

The summation of cation and anion is called the ionic radius of the element. Let us find the ionic radius of Osmium.

The ionic radius of Os is 200 pm which is the same as van der Waal’s radius, because in the ionic form it has the same ionic value.

13. Osmium isotopes

Elements having the same number of electrons but different mass numbers are called isotopes of the original element. Let us discuss the isotopes of Osmium.

Osmium has 46 isotopes based on their neutron numbers which are listed below:

  • 161Os
  • 162Os
  • 163Os
  • 164Os
  • 165Os
  • 166Os
  • 167Os
  • 168Os
  • 169Os
  • 170Os
  • 171Os
  • 172Os
  • 173Os
  • 173Os
  • 174Os
  • 175Os
  • 176Os
  • 177Os
  • 178Os
  • 179Os
  • 180Os
  • 181Os
  • 181m1Os
  • 181m2Os
  • 182Os
  • 183Os
  • 183mOs
  • 184Os
  • 185m1Os
  • 185m2Os
  • 186Os
  • 187Os
  • 188Os
  • 189Os
  • 189mOs
  • 190Os
  • 190m1Os
  • 191Os
  • 191m1Os
  • 192Os
  • 192mOs
  • 193Os
  • 194Os
  • 195Os
  • 196Os
  • 197Os

Stable isotopes are discussed in the below section among 46 isotopes of Osmium:

No. of
184Os  0.02%1.12 * 1013 yα104
183Os  Synthetic93.6 d105
186Os1.59%2* 1015 yα107
189Os  16.15%stableN/A110
190Os  26.26%stableN/A111
191Os  Synthetic15.4 dβ112
192Os  40.78%stableN/A113
193Os  Synthetic30.11 dβ114
194Os  Synthetic6 yβ115
Isotopes of Osmium

Only 11 isotopes are stable of Os among all isotopes, so they also emit any radioactive particles. 183Os,191Os,193Os and 194Os are the only synthetically prepared isotope of Osmium among all and the rest of them are naturally obtained.

14. Osmium electronic shell

The shell surrounding the nucleus as per principal quantum number and holding the electrons is called an electronic shell. Let us discuss the electronic shell of Osmium.

The electronic shell distribution of Osmium is 2 2 6 2 6 10 2 6 10 14 2 6 2 6 because it has s, p, d and f orbitals around the nucleus. Since it has more than 72 electrons and in order to arrange 76 electrons, it need 1s,2s,2p,3s,3p,3d,4s,4p,4d,5s,5p,5d,4f,6s orbitals.

15. Osmium electron configurations

According to Hund’s rule, electrons are distributed to the respective orbitals which are known as electronic configuration. Let us discuss the electronic configuration of Osmium.

The electronic configuration of Os is 1s22s22p63s23p6 3d104s24p65s25p64d146s24f145d6 according to Hund’s rule and the Aufbau principle, as it has 76 electrons. To fill all the 76 electrons, Os need s, p, d and f orbitals having the 1st, 2nd, 3rd, 4th,5th and 6th orbitals.

Due to exchange energy, electrons enter first in 6s orbital then 5d.

16. Osmium energy of first ionization

First I.E. is the energy required for the removal of electrons from the valence orbital of its zero-oxidation state. Let us predict the first ionization energy of Osmium.

The first ionization value of Os is 840 KJ/mol because the electron was removed from the filled 6s orbital and the 6s orbital is subject to relativistic contraction. So the energy required to remove an electron from 6s is lesser than other orbital of Os. Also, 6s has a lower shielding effect.

For other elements, the electrons are removed from p, d or f orbitals depending on their electronic configuration and the last valence orbital.

17. Osmium energy of second ionization

Second I.E. is the energy required for the removal of one electron from the available orbital of +1 oxidation state. Let us see the second ionization energy of Osmium.

The 2nd ionization energy of Os is 1600 KJ/mol which occurred from its 6s orbital, where the remaining electrons after the 1st ionization will be removed. So, when an electron is removed from its excited state, it require higher energy than the previous one.

Generally, 2nd ionization energy is greater than 1st ionization energy because it occurs from a more excited state or inner orbital.

18. Osmium energy of third ionization

Removal of third electrons from the outermost or pre-ultimate orbital of an element having a +2 oxidation state is the third I.E. Let us predict the 3rd I.E. of Osmium.

The third ionization energy of Os is 2220 KJ/mol because the third ionization occurs from partially filled 5d orbital. Due to poor shielding effect and exchange energy of 5d, the attraction of nucleus on the outermost electron is very high and require a higher amount of energy to remove electrons.

For Os, after the removal of the third electron it gains extra stability due to the half-filled 5d configuration.

19. Osmium oxidation states

During bond formation, the charge that appears on the element is called the oxidation state. Let us predict the oxidation state of Osmium.

Os shows variable oxidation states from 0 to +8, but the most common oxidation state of Os are +2,+4,+6 and +8, where it can form stable compounds like OsO4. Due to the presence of 4f, 5d and 6s orbitals, it can show different oxidation states to gain stability.

20. Osmium CAS number

CAS number or CAS registration for any element is used to identify the element which is unique. Let us know the CAS number of Osmium.

The CAS number of Osmium is 7440-04-2 which is given by the chemical abstracts service.

The CAS number of Os is unique and it does not match with other element’s CAS number.

21. Osmium Chem Spider ID

Chem Spider ID is the particular number for a particular element given by the Royal Society of Science to identify their character. Let us discuss it for Osmium.

22379 is the Chem Spider ID for Osmium which is given by the RSC (royal society of chemistry). By using this number we can evaluate all the chemical data related to Osmium atom. Like the CAS number, it is also different for all elements.

22. Osmium allotropic forms

Allotropes are elements or molecules with similar chemical property but different physical properties. Let us discuss the allotropic form of Osmium.

Os has no allotropic form like other transition metals because they cannot show the catenation property like carbon elements.

23. Osmium chemical classification

Based on the chemical reactivity and nature, elements are classified into some special class. Let us know the chemical classification of Osmium.

Osmium is classified into the following categories:

  • Os is a heavier transition element
  • Os is an oxidizing agent
  • Os is also classified as reactive based on the reaction tendency towards carbonyl.
  • Os is more brittle and carry electricity as per electrical conductance.

24. Osmium state at room temperature

The physical state of a particular atom is the state at which an element can exist at room temperature and standard pressure. Let us predict the state of Os at room temperature.

Osmium exists in a solid state at room temperature because it has a crystal lattice that it adopts in the hexagonal structure, where van der Waal’s force of attraction is so high. Also, the layers are present over one another, so it is soft in nature.

25. Is Osmium paramagnetic?

Paramagnetism is the tendency of magnetization in the direction of the magnetic field. Let us see whether Osmium is paramagnetic or not.

Osmium is paramagnetic in nature due to the presence of four unpaired electrons in the valence or outermost 5d orbital and the magnetic value will be 4.89 B.M. which is a spin-only magnetic value. It has a molar magnetic susceptibility value of +11×10−6 cm3/mol.


Os is a 5d transition metal element, due to the presence of four unpaired electrons. It is subject to Jann-Teller distortion in its geometry. It can form many organometallic compounds and due to more d electron, it can bind with soft ligand which can be sigma donor and π acceptor like carbonyl.