Helium (He) and Neon (Ne) are both classified in the same group, Group 18 or Group 8A, in the periodic table. This group is also known as the noble gases or inert gases.
While it is true that helium has only 2 valence electrons and neon has 8 valence electrons, the group assignment is based on the similarity in their electron configurations and their stable electronic structure.
Both helium and neon have completely filled electron shells, which gives them high stability. Helium has its first energy level filled with 2 electrons (1s²), and neon has its second energy level filled with 8 electrons (2s² 2p⁶). This stable electron configuration makes both helium and neon unreactive and chemically inert, which is a characteristic of noble gases.
The grouping of elements in the periodic table is primarily based on the patterns and trends observed in their electron configurations, chemical properties, and reactivity. In the case of helium and neon, despite having different valence electron counts, their overall similarities in electron configuration and chemical behavior place them in the same group.