Halogens — Overview & Properties

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What are Halogens?

They are elements which can be found in group (column) 7A on the periodic table. These elements share similar chemical characteristics. These elements are fluorine ( $F$ ), chlorine ( $Cl$ ), bromine ( $Br$ ), and iodine ( $I$ ). Astatine ( $At$ ) and Tennessine ( $Ts$ ) are also considered halogens, but do not have all the same characteristics as the first four halogens in the group.

Properties of Halogens

Halogens share similar properties these include:

Non-metals.
Diatomic (two atoms) molecules.
Electrophilic or accept electrons.
Reactive in elemental form.
They are commonly found in ionic compounds as the anion with a -1 charge.
They are also found in covalent compounds. For example, in organic chemistry, they often bond to carbon.
React with hydrogen to form water soluble acids.

Trends in Halogen Group

There are some trends that exist in groups on the periodic table.

As we move down the halogen group ( $F$ to $I$ ) there is an increase in:

Atomic weight
Atomic radius
Ionic radius
Melting point
Boiling point
Density

As we move down the halogen group ( $F$ to $I$ ) there is a decrease in:

Reactivity
Electronegativity (affinity for electrons)
Abundance on Earth

Fun Facts

There are different uses for each halogen.

Fluorine is so reactive that the only elements it doesn't react with are the noble gases. $F$ is widely used to make different polymers or plastics. A well-known use for $F$ is as an additive to toothpaste and water, which helps to prevent tooth decay.

Chlorine is widely used in many different compounds which are called chlorinated compounds. These compounds can be used in plastic, solvents, and more. You probably are familiar with the smell of $Cl$ as it is used in swimming pools to kill bacteria.

Bromine is found in photographic film, flame retardants, pesticides, and more. Salt lakes and other high salt bodies of water contain higher amounts of $Br$ than other places on the planet.

Iodine is the safest halogen to handle and is used as a skin disinfectant. $I$ is essential for human diets and is added to some foods. An example is iodized salt containing table salt and iodine salt compounds. However, too much $I$ in the diet or other exposure can damage the thyroid gland in humans. $I$ can undergo sublimation when left alone in a container. This means that the solid $I$ turns into a gas without moving into the liquid phase.