Which group has one valence electron?

• A. The alkali metals
• B. The alkaline earth metals
• C. The halogens
• D. The noble gases

Answer: (A)

Valence electrons are the electrons in the outermost shell that participate in bonding. Elements in the alkali metals group have one electron in their outermost shell, which they readily lose to form a stable configuration like the previous noble gas, giving them a +1 charge. That single outer electron is what defines this group. The alkaline earth metals have two valence electrons, the halogens have seven, and the noble gases have a full outer shell (eight, except helium with two). So the group with one valence electron is the alkali metals.