What elements have a filled outermost energy level?

Elements with a filled outermost energy level are considered to be stable due to the full complement of electrons. These elements typically fall under the noble gases group in the Periodic Table, such as helium, neon, argon, krypton, xenon, and radon. The filled outermost energy level results in these elements having little to no reactivity with other elements, making them chemically inert.