Noble gases

The noble gases, also known as inert gases, are a class of elements that have analogous properties. All noble gases are colourless, odourless, and monatomic gases with low chemical reactivity and stable electronic configurations. The word ‘noble gas’ is derived from a German word called ‘Edelgas’, which means noble gas. Here is an example of noble gases: 

1. Helium
2. Neon
3. Argon
4. Krypton
5. Xenon
6. Radon

They are present in group 18 of the periodic table. Under normal conditions, these elements are in a gaseous state. Noble gases are monatomic gases because they don’t form molecules very easily because of their stable electronic configuration feature. 

Properties of noble gases

Noble gases have several chemical and physical properties, both of which are discussed below.

Chemical properties of noble gases

• They are colourless and odourless. 
• They are monatomic gases.
• They have low chemical reactivity.
• They conduct fluorescence and electricity, which is necessary for certain conditions to sustain a stable environment.
• They are insoluble in water.
• They are very stable because these gases have a complete octet. They rarely react with any other elements because they have a low tendency of losing and gain electrons. However, Xenon is an exception as it can form compounds with oxide or fluoride.

EXAMPLE -XeF4, and XeF6,XeO3

Physical properties of noble gases

Here are some physical properties of noble gases:

Atomic Size or Atomic Radii

Moving down the group from He to Rn, the atomic radii or size increases. This happens because as we move down the group, occupied shells increase in number. 

Melting and boiling point

In normal conditions of atmospheric pressure and temperature, all the noble gas elements are in the gaseous state. All of the noble gases have very low melting and boiling points. However, as we move down the group, the melting and boiling point increases because of the increase in atomic size. 

Density

All the noble gas elements have low densities. However, as we move down the group, the density will increase again due to an increase in atomic size.

Ionisation potential

As we move down the group from He to Rn, atomic size increases which result in an increase in the attractive force and thus, the polarity increases and ionisation potential decreases.

Ionisation energy

On moving top to bottom in a group of the periodic table, the ionisation energy keeps decreasing. These noble gases have the most ionisation enthalpy in the periodic table. This indicated that noble gases are chemically inert.

Heat and electricity conductivity

All of the noble gas elements conduct electricity except neon. All of them are, however, poor heat conductors.

It is important to note that most of the properties of noble gases are correlated to the atomic radii of atomic size. 

We will now discuss some examples of noble gases in detail.

Helium

The first chemical element in group 18 is Helium which is denoted by He. Helium has the lowest boiling point amongst all of the noble gases and it is also the lightest gas in group 18. 

Helium is the second lightest chemical element that is odourless, tasteless and colourless. Helium’s atomic number is 2 and its electronic configuration is 1s2. Thus, Helium has 2 electrons in total in the valence shell. Helium comprises around 23% of the universe’s mass. It’s density is 0.178 X 10-3 g/cm3 at 20°C. It is generally concentrated in stars and is widely used for welding metals like aluminium.

Neon

The second element in the noble gases periodic table is neon which is denoted by Ne. Neon has the atomic number 10. It is a colourless, odourless, tasteless and monatomic gas. Neon is also lighter than air. It has the electronic configuration of [He]2s22p6 and a density of 0.9 g/L. Its melting point is -248.4°C and its boiling point is -246°C. 

Neon is widely used in electrical signs and fluorescent lamps. It is present in less quantity in the earth’s atmosphere. The gas is trapped within the rocks present in the earth’s crust. 

Argon

It is the third element in group 18 in the noble gases periodic table. Argon is denoted by Ar and it has an atomic mass of 18. It is an odourless, tasteless and colourless gas and its electronic configuration is [Ne]3s23p6. It has a density of 1.784 g/L. Argon has a total of 8 elements in its valence shell which is why it is non-reactive. Argon has a melting point of -189.4°C and a boiling point of -185.8°C.

Krypton 

The fourth chemical element in group 18 is Krypton which is denoted by Kr. Krypton has atomic number 36 and it is approximately 3 times heavier as compared to air. Just like other gases in the group, krypton is also colourless, monoatomic, tasteless and odourless gas. Krypton has an electronic configuration of [Ar]3d104s24p6 and a melting point of -157.4°C. It has a boiling point of -153.4°C and a density of 1.784 g/L.

Xenon

The fifth chemical element in group 18 is Xenon which is represented by Xe. Xenon is around 4.5 times heavier than air and like other noble gases, it is colourless, odourless and tasteless. The word Xenon is derived from Xenos, which is a Greek word that means foreign or strange. 

The atomic number of Xenon is 54 and density of 5.761 kg/m3. Its melting point is -157.4°C and a boiling point of -108.1°C. The electronic configuration of this element is [Kr]4d105s25p6.

Radon

The sixth chemical element in group 18 is radon which is represented by Rn. Its atomic number is 86. Radon is a radioactive gas that is produced by the radioactive decay of an element known as radium. Radon is a colourless gas that is approximately 7.5 times heavier than air and around 100 times heavier as compared to hydrogen. The boiling point of radon is -61.7°C and its melting point is -71°C. The electronic configuration of Radon is [Xe]4f145d106s26p6 and density of 9.73 g/litre. Radon is radioactive, which is why it is used to treat cancer.

Conclusion 

Noble gases are present in group 18 of the modern periodic table. They all are colourless, odourless and tasteless. Under normal conditions, they are in a gaseous state. They are monatomic gases because they don’t form molecules very easily, which is because of their stable electronic configuration feature. Now that you have a good idea about noble gases, their physical and chemical properties you are ready to learn about other topics such as properties of alkaline earth metals and more.