Osmium: Occurrence, Properties, Uses and Isotopes of Osmium

Introduction to Osmium Element

Osmium is the transition metal element located in group 8 and period number 6 of the periodic table. Its atomic number is 76 whereas its atomic mass is 190.23. the single neutral atom of osmium contains 76 electrons. The nucleus of the osmium atom contains 76 protons and 116 neutrons. Osmium is represented by the symbol “Os”.

Naming and History

The name of the element Osmium is derived from the Greek word “osme” which means “the smell”. The name was given by Smithson Tennant due to its characteristic unpleasant smell.

  • Smithson Tennant

In 1803, an English chemist Smithson Tennant discovered the osmium element in London. The element was discovered when he dissolved the platinum in dilute aqua regia (aqua regia: a mixture of hydrochloric and nitric acid).

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He observed that the whole metal was not dissolved and resulting substance was black metallic powder. Some scientists believed that it was graphite but Tennant has working experience with carbon so he knew that it was not graphite.

He performed further experiments. He treated metallic powder with sodium hydroxide and heated it till the solution. Then he removed alkali by adding water from the residue. He added hydrochloric acid to the residue and formed an acidic solution.

He observed that alkaline solution contained the new element osmium and acidic solution contained the element iridium which he discovered later in the same year.

Occurrence of Osmium

Osmium mostly exists in a combined form with platinum and iridium. It is mostly obtained from the platinum sands or the major ores which contain osmium are osmiridium and iridosmine. Some amounts are also found in nickel sands. It is mostly obtained from the Americas, Russia, Urals, etc.

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Properties of Osmium

Osmium is a bluish-white, lustrous, brittle, hard, and rare transition element. It is the densest of all the known metals. It remains unaffected by water and acids but it dissolves in molten alkalies. In powder form, when expose to air, it reacts slowly to give osmium tetraoxide vapor.

The melting point of osmium is 3033 °C and its boiling point is 5012°C. The density of osmium is 22.57 grams per cubic centimeter. It exists in the solid phase at room temperature.


Biological Importance of Osmium

There is no known role of osmium in living systems. It is not considered to be toxic but its volatile vapors are toxic and irritating. The poisonous osmium tetraoxide vapor can cause lungs and skin damage. It causes severe irritation to the eyes.

Uses of Osmium

There are few uses of osmium due to its toxic vapors and hardness.

  1. Previously, it was used in the nibs of high-quality fountain pens.
  2. It is used in needles of gramophones, contacts, and clock bearings.
  3. Today, it is alloyed with the metals of the platinum family to make them hard.
  4. 10% osmium and 90% platinum alloys are used in making surgical implants, dental tools, pacemakers, etc.
  5. Osmium tetraoxide is used in the detection of fingerprints in forensic and as a stain for fatty tissues.
  6. Sometimes, it is used as a catalyst in the chemical industry.
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Isotopes of Osmium

There are almost 34 known isotopes of osmium whose mass number ranges from 162 to 196. The most common and stable isotope of osmium is Os- 192 with an abundance of 40. 8%.