Noble gases are characterized by having full outer electron shells, which means they possess the maximum number of valence electrons that their outer shell can accommodate.

Also known as inert gases, noble gases occupy Group 18 (VIII) of the periodic table. This group comprises helium ($\text{He}$), neon ($\text{Ne}$), argon ($\text{Ar}$), krypton ($\text{Kr}$), xenon ($\text{Xe}$), and radon ($\text{Rn}$). The defining feature of these elements is their complete outer electron shells, a consequence of their specific electron configurations.

The electron configuration of an atom illustrates how electrons are distributed within its atomic orbitals. The outermost shell, referred to as the valence shell, plays a crucial role in determining the chemical properties of the element. For noble gases, the valence shell is fully occupied by electrons. This configuration allows them to have either two or eight valence electrons, depending on the element. For instance, helium contains two valence electrons in its sole shell, while neon has eight valence electrons in its second shell.

This complete outer shell contributes to the stability of noble gases’ electron configurations. As a result, these elements exhibit a low tendency to gain or lose electrons, rendering them chemically inert. This inertness is why they are commonly referred to as inert gases. The stability associated with a full outer shell corresponds to the lowest possible energy state for an atom, a state that all atoms strive to attain.

In contrast, other elements in the periodic table lack full outer shells and tend to engage in chemical reactions with other elements to achieve a more stable electron configuration. This pursuit of stability is the fundamental driving force behind chemical reactions. However, since noble gases already possess stable electron configurations, they exhibit minimal reactivity. Consequently, they are found in their elemental form in nature and are utilized in various applications where a non-reactive environment is essential, such as in light bulbs and neon signs.