The noble gases have neutral charges. Because these elements have full outer electron shells, they are resistant to bonding with other elements. Scientists long thought that these elements were completely inert.
Reactivity of elements derives from the number of unfilled electrons in the outermost valence shell. The noble gases comprise the column of the periodic table with completely filled outer shells. All of the noble gases have eight electrons in their outermost valence shells, except for helium, which has just two. Because much of an element's behavior is governed by its reactivity, the noble gases behave in very similar ways.