Which property of alkali metals makes them highly reactive?

Alkali metals are highly reactive primarily due to their electronic configuration. These elements possess one valence electron in their outermost shell. This singular electron is not tightly bound to the nucleus, which makes it relatively easy for the atom to lose it during chemical reactions. When alkali metals lose this valence electron, they achieve a more stable electronic configuration that resembles the nearest noble gas.

The ease of losing this one electron leads to the formation of positive ions and allows alkali metals to readily participate in chemical reactions. This characteristic is a significant factor in their high reactivity, particularly with nonmetals and water. This behavior differentiates alkali metals from other groups, where elements may have different numbers of valence electrons influencing their reactivity.