Osmium
Definition and meaning of Osmium in chemistry.
![Osmium element card: symbol Os, atomic number 76, atomic mass 190.23, electron configuration [Xe] 4f¹⁴ 5d⁶ 6s², oxidation states +4, Transition metal, group 8, period 6, solid at room temperature.](/assets/images/terms/osmium-chemical-element.webp)
Osmium is a chemical element with the symbol Os and atomic number 76. Scientists recognize it as the densest naturally occurring element on our planet. This transition metal is hard, extremely brittle, and bluish-white in color.
In more detail
Osmium sits in group 8 of the periodic table as a transition metal. It proudly belongs to the prestigious platinum group of chemical elements. You will typically find osmium in nature as a completely uncombined metal.
You can also discover it in natural alloys like iridosmine and osmiridium. Miners often extract these specific ores right alongside natural platinum deposits. Osmium boasts an extraordinarily high melting point compared to most other metals.
It also shows a remarkable resistance to both corrosion and harsh chemical attack. The metal has one of the lowest compressibilities of any known element. Compressibility measures how much a substance shrinks when put under extreme pressure.
This very low compressibility makes solid osmium exceptionally stiff and physically hard. Solid bulk osmium remains highly unreactive under normal room temperature atmospheric conditions. However, finely divided osmium powder behaves much differently in the open air.
The powder reacts slowly with atmospheric oxygen at normal room temperatures. This slow chemical reaction forms a new compound called osmium tetroxide (OsO4). Osmium tetroxide is an extremely toxic chemical with a strong, pungent odor.
This compound is highly volatile, which means it evaporates into a gas very easily. Osmium displays an unusually wide range of different chemical oxidation states. An oxidation state describes how many electrons an atom has lost or gained.
These available states range from -2 all the way up to a +8 charge. The +4 and +8 states are the most common in typical osmium compounds. Engineers rarely use pure osmium in its natural elemental form today.
The pure metal is incredibly scarce and very difficult to shape or machine. Furthermore, the highly toxic nature of its oxide makes it dangerous to handle.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Os |
| Atomic number | 76 |
| Atomic mass | 190.23 u |
| Category | Transition-Metal |
| Density near room temperature | 22.59 grams per cubic centimeter |
| Melting point | 3033 degrees Celsius |
| Year of discovery | 1803 by Smithson Tennant |
Manufacturers often combine osmium with other platinum-group metals to create tough alloys. They use these strong alloys to build extremely wear-resistant industrial components. Common examples include electrical contacts, instrument pivots, and high-quality fountain pen tips.
Frequently asked questions
Why does osmium have the highest natural density?
The high density of osmium comes from the lanthanide contraction. This effect pulls the electron cloud tightly toward the highly charged nucleus. It packs a huge amount of mass into a very small volume.
What makes osmium tetroxide particularly hazardous?
Osmium tetroxide is highly toxic because it easily turns into a gas. This gas penetrates biological tissues and destroys vital lipids. It causes severe damage to the human respiratory system and eyes.
Related terms
Sources & references
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