Halogen

Halogen is the name given to group 17 of the periodic table, a group of elements organized by chemical properties. The most common members are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements share the characteristic of having seven electrons in their outermost shell, which makes them readily reactive with other elements.

Because of their high reactivity, the halogens do not occur naturally in elemental (independent atom) form, but are found in compounds, such as ordinary salt, sodium chloride. When they gain one electron, they form a negative ion called a halide.

General properties

The halogens show a regular pattern of properties as you move down the group. Fluorine and chlorine are gases in their normal state, bromine is a liquid, and iodine is a solid. Color intensity increases from top to bottom. Fluorine is the most reactive, with reactivity decreasing as you move toward iodine and astatine.

Compounds

Halogens form ionic compounds called halides with metals and other electron-donating elements, for example sodium chloride and potassium iodide. They also form hydrogen halides with hydrogen, such as hydrogen chloride, which becomes a strong acid when dissolved in water. Organic compounds containing halogens are used in medicines, pesticides, and plastics.

Uses

Chlorine is used for water purification and in chemical factories. Fluorine and its compounds are obtained from tooth medicine to protect teeth. Iodine is needed by the human body to produce thyroid hormones and is added to salt. Bromine was formerly used as a flame retardant chemical.