A periodic table is an arrangement of elements based on their atomic numbers and chemical properties.
It is divided into 18 groups and 7 periods running vertically and horizontally respectively.
The atoms of the elements are structured in form of a nucleus and atomic orbitals or shells. The atomic orbitals seat electrons.
The electrons are arranged into the succeeding shells in definite order as 2,8,18, and so on.
The last shell of the atom is known as the valence shell. When an atom is short of electrons or has extra electrons from achieving a stable configuration, this valence shell loses or gains electrons.
Explanation:
Inert gases are nonmetals placed at the extreme right end of the periodic table.
They all together form the 18th group of the period table.
They have stable electronic configuration i.e., all of their electronic orbitals are completely filled.
They have no drive to gain or lose any electrons from their valence orbitals.
Therefore, an atom that can neither gain nor lose electrons is said to be an inert atom.