Valency of Group 8 elements. Animation of the periodic table, showing the valency of the Group 8 elements, the noble gases. The animation starts by showing the whole periodic table, followed by just the Group 8 elements (light blue). The animation then shows the electron configuration of the first three elements in the group: helium (He), neon (Ne), and argon (Ar). These elements have fully occupied outer electron shells, two electrons for helium and eight each for neon and argon. This is highlighted in red in both the electron shell diagrams and the numerical electron configuration below. The stability of an element's outer (valence) electrons determines its chemical and physical properties. For the groups shown here, the number of electrons in an element's outer electron shell (with the exception of helium) corresponds to its group number in the periodic table. Helium, because it is inert and has a full electron shell, is placed with the noble gases in group 8 (also known as group 0, group 18, and group VIIIA).