A lot of Chemistry can be understood by the fact that atoms cannot have more than $$8$$ electrons in the outermost orbit. In fact, atoms try to make their outermost orbit have 8 electrons. It is almost like the goal of atoms.
Some elements like Neon, Argon, etc naturally have $$8$$ electrons in their outermost orbits. They are called inert or noble, because they hardly interact with other elements. They have already attained their goal of $$8$$ electrons in their outermost orbit.