The elements found in Group 7 of the periodic table are known as the Halogens.

The Halogens are a group of non-metal elements that include Fluorine ($F$), Chlorine ($Cl$), Bromine ($Br$), Iodine ($I$), and Astatine ($At$). The term “halogen” translates to “salt-former,” derived from the Greek words “hal” meaning “salt” and “gen” meaning “to form.” This nomenclature arises from the fact that these elements produce salts when they react with metals.

Each halogen possesses seven electrons in its outermost electron shell, which contributes to their high reactivity. They tend to gain an additional electron to achieve a stable electron configuration, resulting in the formation of diatomic molecules in their natural state, such as $Cl_2$ and $Br_2$.

The physical and chemical properties of halogens vary significantly across the group. At room temperature, Fluorine and Chlorine exist as gases, Bromine is a liquid, while Iodine and Astatine are solids. Each halogen exhibits distinct colors and is characterized as a poor conductor of heat and electricity.

When it comes to reactivity, Fluorine is the most reactive of all the halogens, with reactivity decreasing as one moves down the group. This trend can be attributed to the increasing atomic size and the growing number of energy levels, making it more difficult for the outer shell electrons to attract and capture electrons from other elements.

Halogens have numerous applications in various fields. For instance, Fluorine is commonly used in toothpaste to help prevent tooth decay, Chlorine is employed in water treatment processes to eliminate bacteria, and Iodine serves as an effective disinfectant. However, it is important to note that, despite their beneficial uses, halogens can be harmful or even lethal to living organisms in large quantities, necessitating careful handling.