Group 18 Elements: Noble Gases

Group 18 includes six elements: helium, neon, argon, krypton, xenon, and radon. These elements are all gases characterised by their chemical inertness, forming very few compounds. This unreactivity is why they are termed noble gases. 

The elements in Group 18 have filled valence shell orbitals, which makes them highly unreactive. As a result, they only react with a few elements under specific conditions and are thus referred to as noble gases. The elements in this group have eight electrons in their valence shell, except for helium, which has only two electrons in its valence shell.

1.0Occurrence

All noble gases, except radon, are found in the atmosphere. Their combined abundance is about 1% by volume in dry air, with argon being the most prevalent. Helium and occasionally neon can also be found in minerals of radioactive origin, such as pitchblende, monazite, and cleveite. The commercial source of helium is natural gas. Xenon and radon are the rarest elements in this group, with radon being produced as a decay product of ²²⁶Ra.

2.0Electron configuration

Electron configurations for the noble gases, including their atomic symbols:

• He (Helium): 1s²
• Ne (Neon): [He] 2s² 2p⁶
• Ar (Argon): [Ne] 3s² 3p⁶
• Kr (Krypton): [Ar] 3d¹⁰ 4s² 4p⁶
• Xe (Xenon): [Kr] 4d¹⁰ 5s²5p⁶
• Rn (Radon): [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶

3.0The Atomic and Physical Properties of Noble Gases

4.0Characteristics of Group 18 Elements

Here are the key characteristics of Group 18 elements:

• They have a stable octet configuration with eight valence electrons in the outermost shell, except for helium, which has a duplet configuration with two electrons.
• The atomic radii of noble gases are very small. As you move down the group, the atomic radii increase due to the addition of electron shells.
• Group 18 elements have large positive values of electron gain enthalpy.
• All group members, except helium, have eight electrons in their outermost shell and exhibit an octet configuration, leading to high ionisation enthalpy.
• As you move down the group, the ionisation enthalpy decreases while the atomic size increases.

5.0Physical and Chemical properties of Group 18 elements 

1. Physical Properties:

The physical properties of Group 18 elements are as follows:

• These elements exist in their free state due to their stable nature.
• Noble gases are colourless, tasteless, and odourless.
• They have low solubility in water.
• These gases can be condensed only at very low temperatures
• Helium has the lowest boiling point of all the Group 18 elements.

2. Chemical Properties:

The chemical properties of Group 18 elements are as follows:

• Noble gases are inert due to their stable electronic configuration.
• These elements have high ionisation enthalpy and high positive electron gain enthalpy.
• All Group 18 elements are insoluble in water.
• Noble gases conduct electricity and exhibit fluorescence, which helps maintain a safe environment.
• Krypton forms krypton difluoride, whereas xenon does not, due to krypton's higher ionisation enthalpy.

6.0Uses of Noble Gases

1. Helium is a non-flammable and lightweight gas, making it ideal for filling balloons used in meteorological observations. 

• It is also utilised in gas-cooled nuclear reactors. 
• Liquid helium is used as a cryogenic agent for experiments at extremely low temperatures.
• It is crucial for producing and maintaining powerful superconducting magnets in NMR spectrometers and MRI systems.
•  Helium is also used as an oxygen diluent in modern diving equipment due to its extremely low solubility in blood.

2. Neon is employed in discharge tubes and fluorescent bulbs for advertising, such as neon signs. It is also used in botanical gardens and greenhouses for its distinctive illumination.
3. Argon is mainly used to create an inert atmosphere in high-temperature metallurgical processes, such as arc welding of metals and alloys. It also fills electric bulbs and is used to handle air-sensitive substances in laboratory settings.
4. Xenon and Krypton have fewer significant applications. They are primarily used in light bulbs designed for specialised purposes.