Atoms form chemical bonds to satisfy the OCTET rule and to become STABLE.
The noble gases are the only set of elements that have 8 electrons in their outermost shells and that is why they are stable and unreactive. Other elements in the periodic table have less than 8 electrons in their valence shells and thus, they usually undergo chemical reactions in order to have 8 electrons in their valence shells and to attain stability. The octet rules states that an element must have 8 electrons in its outermost shell in order to be stable.