c. Why are Group 1A (1) and Group 2A (2) elements found in many compounds, but not Group 8A (18) elements?

Group 1A (alkali metals) and Group 2A (alkaline earth metals) elements are highly reactive due to their electronic configurations. Alkali metals have one electron in their outermost shell, while alkaline earth metals have two. This makes them eager to lose electrons and form positive ions, allowing them to easily combine with nonmetals to create various compounds.

Group 8A (noble gases) elements are characterized by their complete valence electron shells, which confer a high degree of stability. This stable configuration makes them largely unreactive and less likely to form compounds. As a result, noble gases do not readily participate in chemical reactions like the more reactive alkali and alkaline earth metals.

The formation of compounds involving Group 1A and 2A elements typically occurs through ionic bonding, where these metals lose electrons to form cations. These cations then attract anions (negatively charged ions) to create stable ionic compounds. In contrast, noble gases do not form ions or compounds due to their lack of reactivity, further explaining their absence in compound formation.