Noble Gases - Physical and Chemical Properties

Introduction to Physical and Chemical Properties of Noble Gases

In the modern periodic table, group 18 belongs to noble gases. This group consists of a chemical series of gases including Argon, helium, neon, krypton, xenon, and radon. Radon is the only radioactive out of all. As the elements of the group hold the maximum number of electrons in their outermost shell so they are considered as the most stable elements of the periodic table. As they are already stable, they react very rarely with the other elements. Noble gases are also known as inert and rare gases. Group 18 was characterized later on as compared to other groups of elements. 

During Mendeleev's time, noble gases were not discovered. In the late 18th century, Henry Cavendish was the first person to discover noble gases which were given the place of zero groups and were renamed as group 18 in the periodic table by the IUPAC convention.

Chemical Properties of Noble Gas

There are various chemical properties of inert gases that are mentioned below:

1) Characteristics of noble gases are odorless, non-flammable, colorless, and monoatomic gas with low chemical reactivity.

2) All the noble gases conduct electricity and fluorescence which can be needed in many conditions to maintain a constant and safe environment.

3) All noble gases are insoluble in water.

4) As they have a complete octet which makes them highly stable. So, they hardly react with other elements to form chemical bonds because of their less tendency to either gain or lose electrons. But as exceptions are everywhere. Xe is the exception in this case. Xenon is the noble gas that may form compounds either with fluoride or oxide.

For Example

1) Xenon Oxide

Xenon Tetroxide (XeO4) is a yellow crystalline solid which is relatively stable. Xenon can bring up to its highest oxidation state of +8 only by the one element that is known as oxygen.

2) Xenon Fluorides 

Xenon Difluoride (XeF2) is a dense, white crystalline solid having a linear geometry. It is considered as a powerful fluorinating agent. It has low vapor pressure and is sensitive to moisture.

Physical Properties of Noble Gases

Following are several physical properties of inert gases:

1) Atomic Radii (Atomic size)

As we move down the group from helium to radon the atomic size of noble gases keeps on increasing. This is because when going down the group, the number of occupied shells with valence electrons increases.

2)Boiling and Melting Points 

  • At room temperature and pressure, all the elements of group 18 exist in a gaseous state.

  • The melting and boiling point of all the noble gases is very low due to the following reasons:

  •  All consist of monatomic molecules that are held together by weak van der Waal forces of attraction.

  • During melting and boiling of overall noble gases, and only a slight amount of heat is required to resist weak interatomic force.

  • But, As we move down the group, the boiling and melting point of the noble gases increases due to the following reason:

  • When moving down in the group, the atomic radii increases which results in the formation of a strong Van Der Waals force of attraction between the atoms.

  • As to overcome the interatomic force of attraction which becomes stronger, it also requires more energy during melting and boiling.

3) Density

All elements of group 18 have low densities. When going down the group, density increases as the atomic mass keeps on increasing.

4) Ionization Energy

In the periodic table, As we move down the group the first ionization energy keeps on decreasing. Noble gases have the highest ionization enthalpy from all the groups of the periodic table, reflecting that they are chemically inert.

5) Ionization Potential

When going down the group, the atomic radii increase which increases the attractive force and ultimately results in the increase of polarity and decrease in the ionization potential. This is because the larger atom of the group in the valence electrons are held together less tightly by the atom as they are situated far away from the nucleus.

6) Electrical and Heat Conductivity

All noble gas except neon conducts electricity. All the inert gases of group 18 are poor conductors of heat.

Note: Several properties of the noble gases on the periodic table are positively correlated to the atomic size.

The Following Table Shows Some Physical Properties of Inert Gas







Atomic Radius (nm)












Boiling Point (°C)






Melting Point (°C)






FAQ (Frequently Asked Questions)

1.Why Noble Gases are Known as Inert Gases and What are the Properties of Inert Gases?

Under normal conditions, the outermost shell of the noble gases is completely filled which results in less tendency of either gain or loss of electrons by the noble gases to form a chemical bond which makes them chemically inert and non-reactive.

Properties of inert gases are:

  • Except for Helium, all the elements of group 18 have 8 electrons in their outermost shell which makes them highly stable as they do not share, accept, or release electrons. This results in making them chemically inert or chemically unreactive.

  • Helium has only two electrons in its outermost shell which is a duplet electron arrangement that is also very stable.

2. What are the Uses of Noble Gases?

  • Helium is used to fill airships and weather balloons because it has a good flame level and is very light.

  • Neon is used to fill advertising light bulbs and in small neon lights.

  • Argon is used for the purpose of welding for creating an inert environment and filling the electric bulbs.

  • To repair the retina of the eye, krypton is used in lasers.

  • Xenon is used in electron tubes and bubble chambers.

  • Radon being radioactive is used to treat cancer.