Monoatomic gases as the name suggests are gases consisting of single atoms. They are widely studied in physics and chemistry. The elements in the gas exist as stable single atoms and are not bound to each other by any chemical bond. In this article, we discuss the definition, degrees of freedom, and examples of monoatomic gas.
Monoatomic gases definiton
- Monatomic gas exists as a single atom and does not bound to each other.
- They are stable at standard room temperature.
- There is no chemical bond involved in these gases.
- They are very unreactive due to the completely full outer valence shell.
- Since they are inert they don’t react easily to form compounds.
- They are generally odorless, tasteless, and colorless
- They also have low freezing and boiling point
[Note: Nitrogen is an inert gas. It exists in a diatomic form as N2 gas. That means it is only stable when it is bonded to another nitrogen atom]
Example-list of monoatomic gases
- Helium
- Neon
- Argon
- Krypton
- Xenon
- Radon
- Oganesson
Helium (He)
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- Helium gases were first discovered in 1868
- Helium is the second element in the periodic table with an atomic number of 2.
- Helium is a very light gas even lighter than air. That is why air balloons use helium gas to fly. It also has a very low density.
- Helium is used in medicine to treat respiratory ailments and is also a cooling agent for magnets used in MRI
- Helium is used in laser guns used to scan barcodes
- Helium is a major component (~80%) in an artificial diving environment.
Neon (Ne)
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- Neon was first discovered in 1898.
- It is an abundantly available material and widely used in vacuum tubes and other electrical equipment like switching gears, laser guns, etc
Argon (Ar)
- Argon was first discovered in 1894
- It is a very inert gas and is used for high-tech applications where very inert gases are required.
- Argon is also used in welding and in bulbs as an inert gas.
krypton (Kr)
- Krypton was first discovered in 1898 and is a very rare gas.
- Krypton is a highly unreactive gas but is known to have a reaction with fluorine gas.
- Krypton is used in flash lamps for high-speed photography
Xenon (Xe)
- Xenon was first discovered in 1898.
- Xenon is a highly unreactive gas but applications are limited due to the cost of xenon gas.
- Xenon gas is also used in medicine as general anesthesia.
- The radioactive isotopes of xenon gas are used in nuclear reactors.
Radon (Rn)
- Radon was first discovered in 1900.
- Radon is an inert gas but is highly radioactive.
- Radon is widely used in cancer therapy.
- It is not very abundant in nature and hence has limited use.
Oganesson (Og)
- Oganesson was first discovered in 2006.
- Oganesson is a highly radioactive gas
Are monoatomic gases ideal?
An ideal gas is a theoretical case in which the molecules of the gas do not interact with each other. Such a gas follows the ideal gas law PV=nRT at all pressure and temperature. But, all real gases have intermolecular interactions. So, monoatomic gases are not ideal gases.
What are the Degrees of freedom for a monoatomic gas?
The atoms in a monoatomic gas exist in a single-atom form, so they can move in any direction in space. Hence, they have 3 degrees of motion. In comparison, a diatomic gas has 6 degrees of freedom.
What is the difference between monoatomic and diatomic gases?
The monoatomic gas has one atom per molecule like He or Ne etc.
| Monoatomic gases | Diatomic gases |
| Monoatomic gases have one atom per molecule | Diatomic gases have two atoms per molecule |
The internal energy of monatomic gas is (3/2)RT | The internal energy of diatomic gas is (5/2)RT |
| Examples: Helium(He), Neon(Ne) etc | Examples: Nitrogen(N2), oxygen(O2) etc |
