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

Chemical reactivity refers to the tendency of a substance to undergo chemical changes, forming new compounds. Group 1A (alkali metals) and Group 2A (alkaline earth metals) elements are highly reactive due to their desire to lose electrons and achieve a stable electron configuration. In contrast, Group 8A (noble gases) elements have a complete valence shell, making them largely inert and unreactive, which explains their scarcity in compounds.

Electron configuration describes the distribution of electrons in an atom's orbitals. Group 1A and 2A elements have one and two electrons in their outermost shell, respectively, which they readily lose to form positive ions. This loss of electrons leads to the formation of ionic bonds with nonmetals, resulting in a variety of compounds, while Group 8A elements possess a full outer shell, making them stable and unlikely to form bonds.

Ionic and covalent bonding are two primary types of chemical bonds. Group 1A and 2A elements typically form ionic bonds by transferring electrons to nonmetals, resulting in the formation of stable ionic compounds. In contrast, Group 8A elements do not participate in bonding due to their stable electron configuration, which limits their ability to form compounds, thus explaining their absence in many chemical reactions.