Answer – Noble gases are unreactive as their valence shells, or outermost electron shells, are completely filled.
Explanation:
The elements that make up the last group in the periodic table are called noble gases. One of the defining properties of this group is the unreactivity of these elements. This means that they remain inert, and it is very difficult to involve these gases in chemical reactions.
An important feature of the reactivity of elements is the state of their valence shells of their atoms – when these are not filled to their capacity (2 or 8 electrons), the atoms readily engage in reaction with other atoms where electrons are donated, received or shared. This is to ensure that their valence shells are filled, and hence, stable.
The valence shells of the atoms of all noble gases are filled to capacity, i.e. all of them have 8 electrons in their valence shells (an octet configuration), with the exception of helium (He), which has two (a duplet configuration). Since these atoms are already in their most stable states, they do not need to react with other atoms to achieve stability. Thus, noble gases are unreactive.
