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Osmium is an element with the symbol Os and atomic number 76 which is a hard, brittle, bluish-white platinum-group transition metal found as a trace element in alloys, mostly platinum ores. Discovered by Smithson Tennant in 1803, Osmium is a very dense, blue-white hard metal. The oxides of Osmium give off highly toxic gases and form easily when the metal is exposed to air. As such, there are few commercial uses for osmium other than as a minor alloying agent where it reduces frictional wear. Most osmium is obtained as a by-product from the refining of platinum and nickel ores.
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Key Terms: Osmium, Element, Atomic Number, Melting Point, Boiling Point, Platinum Metals, Oxidation State, Alkalis, Temperature, Periodic Table
What is Osmium?
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Osmium is the densest naturally occurring element. Osmium is a lustrous and silvery metal with an atomic number of 76 on the periodic table. It tends to be a dense metal. It appears as a bluish metal and is found in the platinum group.
Osmium
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| Chapter Related Topics | ||
|---|---|---|
| Lanthanide Contraction | Ammonium Persulfate | Gadolinium |
| Ammonium Acetate | Hydrogen Chloride | Actinoids |
Chemical Properties of Osmium
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Compounds are formed from osmium, whose oxidation states range from -2 to +8. The major natural oxidation states are +2, +3, +4, and +8 of which +8 is notable because it is the highest attained by any chemical element other than iridium +9, and is found only in ruthenium, xenon, iridium, and hassium.
Although there is a wide range of compounds in multiple oxidation states, at standard pressure and temperature, osmium forms in large quantities, which can resist attack by all acids (including aqua regia), although molten alkalis will attack osmium.
Physical Properties of Osmium
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The physical properties of Osmium are:
- Osmium is twice as dense as lead and slightly denser than iridium.
- It is a shiny metal that shines even at high temperatures.
- It has a high bulk modulus of between 395 and 462 GPa.
- It is quite hard and has low vapour pressure.
- For these reasons, solid osmium metal is difficult to shape.
The main properties of Osmium are tabulated below:
| Atomic Number | 76 |
| Atomic Weight | 190.2 |
| Melting Point | 3,000°C (5,432° F) |
| Boiling Point | Around 5,000° C (9,032° F) |
| Specific Gravity | 22.48 (20° C) |
| Oxidation States | +2, +3, +4, +6, +8 |
| Electron Configuration | [Xe]4f145d66s2 |
Uses of Osmium
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Some of the major applications of Osmium are as follows:
- Osmium in its pure form is rarely used; rather, this element is alloyed with other metal elements for high-wear applications.
- Osmium alloy tips are mre durable than chrome and steel and more expensive than diamond and sapphire tips. Therefore, its use has been discontinued.
- Osmium tetroxide is used to detect fingerprints and to stain adipose tissue for electron and optical microscopy.
- The Osmium Lamp was constructed in 1898 by Auer von Welsbach using a filament made from osmium. Tetroxide and potassium osmate (the former derivatives) are essential oxidising agents in organic synthesis.
- Similar to palladium, osmium in powder form absorbs hydrogen atoms and can aid in the manufacture of metal hydride battery electrodes.
- Osmium has a clinical application in Scandinavia called synovectomy in patients with arthritis.
- In 2011, two compounds, osmium (II) and osmium (VI) were reported to show anticancer activities in vivo. Therefore, using compounds of osmium as anti-cancer medicines hinted at a hopeful future.
Uses of Osmium
Health Effects of Osmium
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The health issues related to Osmium are given below:
- Health Effects of Osmium Tetroxide, OsO4, is highly toxic. Airborne concentrations as low as 10-7 gm-3 can cause lung congestion, skin damage, and serious eye damage.
- The oxide, in particular, should only ever be handled by a suitably qualified chemist.
- Osmium tetroxide can be ingested into the body by inhaling its vapour, inhaling its aerosol, or ingestion. When evaporating this substance at 200C, harmful contamination of the air can be reached very quickly.
- The substance decomposes on heating, producing osmium fumes. The substance is a strong oxidizer and will react with combustible and reducing substances. Chlorine reacts with hydrochloric acid to form toxic chlorine gas.
- When combined with alkali, it produces unstable compounds. Effects of short-term exposure create tears.
- It turns out to be corrosive to the eyes, skin and respiratory tract. Inhalation of this substance can cause pulmonary edema. Exposure to high levels can cause death. effects may be delayed.
- Repeated or prolonged skin contact may cause dermatitis. The substance may cause kidney effects.
Things to Remember
- Osmium (Os) is the densest naturally occurring element with atomic number 76.
- It is one of the platinum metals of Groups 8–10 (VIIIb) and Periods 5 and 6 of the periodic table.
- Osmium was first discovered in England in 1803 by William Hyde Wollaston and Smithson Tennant.
- Osmium is a grey-white metal, which is very hard, brittle, and difficult to work, even at high temperatures.
- Osmiridium and Iridosmine are the ores of osmium, and this metal is rare in some parts of North America, South America, and also Russia.
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Sample Questions
Ques. What are the uses of Osmium? (3 Marks)
Ans. The uses of Osmium are mentioned below.
- It is used in industry as a catalyst.
- Due to its high reflectivity, it is also of great use in the field of space travel.
- It is used in light bulbs and incandescent lamps to increase light output.
- Osmium tetroxide is used in fingerprint recognition.
- It is used as an electrolyte in battery applications because of its ability to absorb hydrogen atoms. It is used in fountain pen nibs.
Ques. Which countries are the top producers of Osmium? (3 Marks)
Ans. The three top producers of Osmium are
- South Africa
- Russia
- Zimbabwe
Also, these countries are the top reserve holders of the Osmium element.
Ques. What are the oxidation states of Osmium? (3 Marks)
Ans. Osmium exhibits oxidation states from 0 to +8 in its compounds, with the exception of +1; well-characterised and stable compounds contain the element in +2, +3, +4, +6, and +8 states. Also, there are carbonyl and organometallic compounds in the low oxidation states of 2, 0, and +1. Ruthenium is the only other element known to have an oxidation state of 8.
Ques. What are the Isotopes of Osmium? (3 Marks)
Ans. There is a mixture of seven stable isotopes in Natural osmium:
- osmium-184 (0.02 percent)
- osmium-186 (1.58 percent)
- osmium-187 (1.6 percent)
- osmium-188 (13.3 percent)
- osmium-189 (16.1 percent)
- osmium-190 (26.4 percent)
- osmium-192 (41.0 percent)
Ques. What is the Boiling Point of Osmium? (1 Mark)
a) 5027 degree Celsius
b) 5720 degree Celsius
c) 5207 degree Celsius
d) 5072 degree Celsius
Ans. C. 5207 degree Celsius
Ques. Name the densest stable element on the earth? (1 Mark)
a) Osmium
b) Tungsten
c) Aluminium
d) Rhodium
Ans. A. Osmium.
Ques. Can Osmium be melted? (1 Mark)
Ans. Osmium has the highest melting point of any platinum metal. It is unworkable as metal and cannot be melted and shaped like most metals easily. Osmium has very few practical uses owing to its properties.
Ques. Does osmium occur in its pure form? (1 Mark)
Ans. No, the pure osmium metal does not occur in nature as Osmium has a low crystal abundance of about 0.001 parts per million. Although it is rare, osmium is found in native alloys with other platinum metals in siserskite (up to 80 per cent), iridosmine, and in aurosmiridium (25 per cent), and in slight amounts in native platinum.
Ques. Explain the reactions of osmium with air. (1 Mark)
Ans. Osmium is the most rapidly attacked by air out of all platinum metals. The powdered osmium exudes the characteristic odour of the poisonous, volatile tetroxide, OsO4, even at room temperature. Since the solutions of OsO4 are reduced to black dioxide, OsO2, by some biological materials, is used to stain tissues for microscopic examinations sometimes.
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