Valence electrons
All of the elements in Group 18, which are noble gases, have 8 valence electrons because they are stable.
Period 5
Valence electrons differ in the transition metals because they are in the middle and have different characteristics.
electronegativity
Noble gases are unreactive.Electronegativity is defined as the measure of the ability of an atom to attract electrons to itself. Every atom strives to gain 8 electrons, which is the number of atoms in the outermost energy level of an atom. Since the noble gases already have 8 electrons in their outer shells, they dont wan't to attract any more, and since electronegativity measures the amount of attraction between an atom and an electron, noble gases do not have electronegativity.
period 5
Electronegativity differs. The trend isn't smooth throughout the table.