Monatomic gases

Introduction

The term “monatomic” is used both in physics and chemistry. Monatomic is a combination of two words, “mono” and “atomic,” which means “a single atom.” There are many monatomic gases present in the atmosphere. Every chemical element in the gaseous phase at a high temperature is monatomic gas. Specific examples of monatomic gases are helium (He), argon (Ar), and neon (Ne). 

Monatomic gases are widely different from diatomic, triatomic, and polyatomic gases. Their thermodynamic nature is comparatively more straightforward than the other gases. In an average temperature range, the gases do not have the right rotational energy and the vibrational components that can make them behave like other polyatomic gases. Even their heat capacity depends on certain factors such as temperature, molecular or atomic weight, and entropy. 

Examples of monatomic gases

The most prominent examples of monatomic gases include noble gases. Noble gases can be found in the Group 18 of the periodic table. The noble gases consist of helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganesson (Og). These are inert gases tasteless, colourless, odourless, and non-flammable. These fall under the monatomic gases category because they are primarily unreactive. 

Uses of noble gases

• Helium is used to fill up balloons for party decorations. 
• Laser processing requires helium. 
• Electrical instruments require neon to shield them from heavy lighting. 
• Argon gas is used for welding. 
• Xenon gas is useful for photography. 
• Radon can treat tumours. 

What is a monatomic ideal gas?

The behaviour of gas is judged according to the general law of gases. An ideal gas’s physical behaviour corresponds to a specific idealised relationship between pressure, volume, and temperature, known as the public gas law. This law is a generalisation that includes both Boyle’s and Charles’ laws as particular instances that work for a given quantity of gas. A monatomic ideal gas has particles that do not interact and react with the resting centre of mass. 

What are degrees of freedom?

The phrase “degrees of freedom” refers to the number of free or independent motions in the system. In other terms, the degree of freedom is the quantity equal to the number of different sorts of independent movements that a system can have. 

• Monatomic gases have three degrees of freedom. 
• The degrees of freedom in diatomic gases can increase up to five. 
• Triatomic molecules can have around five or six degrees of freedom. 

What are diatomic molecules?

The prefix “di” comes from Greek , which means “two”. Diatomic molecules consist of only two atoms, which can be of the same or distinct chemical elements. A diatomic molecule is considered homonuclear if it contains two atoms of the same component, hydrogen or oxygen. 

Specific examples of diatomic molecules include:

• Hydrogen (H2)
• Nitrogen (N2)
• Fluorine (F₂)
• Oxygen (O₂)
• Chlorine (Cl₂)

What are polyatomic ions?

Ions are molecules or substances that are positively or negatively charged. They are characterised as monatomic when just one atom with either a positive or negative charge is present, diatomic when two particles are present, and polyatomic when more than two atoms are present. For example, nitrate or NO3- has one nitrogen and three oxygen atoms. Hence it is a polyatomic ion. 

An ion that has more than one atom is called a polyatomic ion. It can be either positively or negatively charged. It is a molecular ion. It is formed when two covalent atoms bond with each other. Polyatomic ions are also known as radicals in some cases. 

Specific rules are followed when writing the formula for polyatomic ions. The cation comes first, followed by the anion. 

These are a few examples of polyatomic ions: 

Chlorite ClO₂⁻

Mercury Hg⁺²

Nitrite NO2-

Ammonium NH₄⁺

Bisulfate HSO₄⁻

Phosphonium PH₄⁺

Conclusion

The concept of monatomic gases is relevant both in physics and chemistry. Reading Avogadro’s number, kinetic theory of gases and Newton’s law of motion can help in further understanding the concepts of gases. There are many uses of monatomic or noble gases in our daily lives. Monatomic gases are different from diatomic and polyatomic gases.