The noble gases are the elements in group 0: helium, neon, argon, krypton, xenon and radon. They are chemically inert, which means they do not react with other elements under normal conditions.
The reason is their electronic configuration. Helium has 2 electrons, which fills its first shell. Neon is 2,8 and argon is 2,8,8, so the other noble gases have 8 electrons in their outer shell. A full outer shell is a very stable arrangement.
Atoms of other elements react by gaining, losing or sharing electrons to get a full outer shell. Noble gas atoms already have one, so they do not need to gain, lose or share electrons. They do not form bonds easily and exist as single atoms, which we call monatomic.
