Halogen Elements and Properties

The halogens are a group of elements on the periodic table. It is the only element group that includes elements capable of existing in three of the four main states of matter at room temperature: solid, liquid, and gas.

The word halogen means "salt-producing," because halogens react with metals to produce many important salts. In fact, halogens are so reactive that they do not occur as free elements in nature. Many, however, are common in combination with other elements Here is a look at the identity of these elements, their location on the periodic table, and their common properties.

Location of the Halogens on the Periodic Table

The halogens are located in Group VIIA of the periodic table, or group 17 using IUPAC nomenclature. The element group is a particular class of nonmetals. They can be found toward the right-hand side of the table, in a vertical line.

List of Halogen Elements

There are either five or six halogen elements, depending on how strictly you define the group. The halogen elements are:

• Fluorine (F)
• Chlorine (Cl)
• Bromine (Br)
• Iodine (I)
• Astatine (At)
• Element 117 (ununseptium, Uus), to a certain extent

Although element 117 is in Group VIIA, scientists predict it may behave more like a metalloid than a halogen. Even so, it will share some common properties with the other elements in its group.

Properties of the Halogens

These reactive nonmetals have seven valence electrons. As a group, halogens exhibit highly variable physical properties. Halogens range from solid (I₂) to liquid (Br₂) to gaseous (F₂ and Cl₂) at room temperature. As pure elements, they form diatomic molecules with atoms joined by nonpolar covalent bonds.

The chemical properties are more uniform. The halogens have very high electronegativities. Fluorine has the highest electronegativity of all elements. The halogens are particularly reactive with the alkali metals and alkaline earths, forming stable ionic crystals.

Summary of Common Properties

• They have very high electronegativities.
• They have seven valence electrons (one short of a stable octet).
• They are highly reactive, especially with alkali metals and alkaline earths. Halogens are the most reactive nonmetals.
• Because they are so reactive, elemental halogens are toxic and potentially lethal. Toxicity decreases with heavier halogens until you get to astatine, which is dangerous because of its radioactivity.
• The state of matter at STP changes as you move down the group. Fluorine and chlorine are gases, while bromine is a liquid and iodine and astatine are solids. It is expected that element 117 will also be a solid under ordinary conditions. The boiling point increases moving down the group because the Van der Waals force is greater with increases size and atomic mass. 

Halogen Uses

The high reactivity makes halogens excellent disinfectants. Chlorine bleach and iodine tincture are two well-known examples.

Organobromine compounds—also referred to as the organobromides—are used as flame retardants. Halogens react with metals to form salts. The chlorine ion, usually obtained from table salt (NaCl) is essential for human life. Fluorine, in the form of fluoride, is used to help prevent tooth decay. The halogens are also used in lamps and refrigerants.