The halogens, which include fluorine, chlorine, bromine, iodine, and astatine, have 7 valence electrons. This characteristic is crucial because it influences their reactivity and the types of chemical bonds they can form.
Valence electrons are the electrons in the outermost shell of an atom. Halogens are in Group 17 of the periodic table, and they are known for their high electronegativity and strong tendency to gain one more electron in order to achieve a full outer shell, which is usually 8 electrons (following the octet rule). Thus, with 7 valence electrons, halogens are just one electron short of achieving this stable configuration.
In summary, the correct answer is 7.