What group of elements is characterized by having seven valence electrons?

The group of elements characterized by having seven valence electrons is the halogens. This group includes fluorine, chlorine, bromine, iodine, and astatine. The presence of seven valence electrons means that halogens are highly reactive, as they require only one additional electron to achieve a stable electron configuration, often resembling that of noble gases.

This reactivity is a defining feature of halogens, leading them to readily form bonds with other elements, particularly metals, to create ionic compounds. The characteristics of halogens also contribute to their classification in Group 17 of the periodic table.

In contrast, noble gases have a complete octet of eight valence electrons, making them mostly inert and unreactive. Alkaline earth metals possess two valence electrons, which they readily lose to form cations, while transition metals have varying valence electron counts that can lead to a complex chemistry. Understanding the valence electron structure is crucial in predicting the chemical behavior and reactivity of different groups of elements.