The Group VIII noble gases (Helium, Neon, Argon, Krypton, Xenon, and Radon) are known for their exceptional unreactivity. This unreactivity stems directly from their electronic configuration. Each noble gas possesses a full outermost electron shell, meaning their valence shell (the outermost shell) contains eight electrons, fulfilling the octet rule. This full shell makes them exceptionally stable and prevents them from readily gaining, losing, or sharing electrons with other atoms.

Unlike other elements which tend to react to achieve a stable octet, noble gases have no need to do so. Their electron configuration is already in a very stable state. Therefore, they have very little tendency to form chemical bonds. The high ionization energy required to remove an electron from a noble gas further contributes to their inertness.

In summary, the full valence shell electronic configuration of the noble gases is the fundamental reason for their unreactivity. They are already in a stable, energetically favourable state.

Noble gases are used in lighting for the following reasons:

• Inertness: They are unreactive, so they do not react with the metal components of the light bulb, preventing corrosion and extending the life of the bulb.
• High Ionization Energy: They require a high amount of energy to ionize, meaning they are less likely to lose electrons and create a dull, dark light.
• Low Luminescence at Low Currents: They emit a bright, white light when an electric current passes through them at low voltages.

The principle behind their use is based on electrical conductivity. When a voltage is applied, the noble gas atoms become ionized, meaning they lose electrons and form positive ions. These positive ions, along with the free electrons, create a plasma. The movement of these charged particles results in the emission of light. The specific colour of the light depends on the type of noble gas used. For example, neon produces a reddish-orange light, while argon produces a bluish-white light. The light is brighter and more efficient than that produced by other gases at similar voltages.

The noble gases are typically monoatomic gases because their unreactivity is linked to their stable, filled valence shells. Achieving a stable octet means they have no need to form chemical bonds with other atoms. Chemical bonds typically involve the sharing or transfer of electrons to achieve a full valence shell. Since noble gases already have a full valence shell, there is no benefit to forming a bond.

To form a diatomic molecule, for example, a noble gas would need to gain or lose electrons to achieve a full octet. However, this would disrupt their already stable electronic configuration. Therefore, they exist as individual, independent atoms – hence, monoatomic gases. The stability conferred by their full valence shells makes the energy required to form a bond energetically unfavourable.