Explain that halogens have seven electrons in their outer shell.

Halogens are a group of non-metals found in Group 7 of the periodic table. Each halogen has seven electrons in its outer shell, which is one electron short of a full octet. This configuration makes them highly reactive, as they tend to gain an electron to achieve stability. The presence of seven outer-shell electrons is a key characteristic that defines their chemical behavior, leading to their tendency to form bonds with other elements, particularly metals and non-metals.