Group 17 Elements – What are Halogens?

On the periodic table, the elements Fluorine, Chlorine, Bromine, Iodine, Astatine, and Tennessine together form a group known as Group 17. These elements are not metals (non-metals) but are highly reactive and somewhat similar in terms of their properties, which are not found in other groups of elements on the periodic table. Each of these elements has been discovered by chemists and physicists at different timelines and was named differently than what we know of them today.

What are Halogens?

The elements that collectively form Group 17 are Halogens derived from Greek words wherein ‘halo’ means salt, and ‘genes’ means to produce, as Halogens have salt when they react with metals. Among the six elements in Group 17, Astatine is the only radioactive element known to be the rarest element that forms on the earth’s crust. Halogens react with both metals and nonmetals and, thus, have strong oxidation, with the reaction decreasing from top to bottom in the list of elements.

General Characteristics of Halogen Family

The elements of the Group 17 of the periodic table – Fluorine, Chlorine, Bromine, Iodine, Astatine and Tennessine are non-metals and the only elements that exist in three states of solid, liquid, and gas at room temperature. Because of the high reactivity of Halogens, these are used as disinfectants such as Chlorine bleach and iodine tincture and are also used as flame retardants. When the Halogens react with metals, they form salts that are sodium fluoride and hydrochloric acid, of which Chlorine ion is obtained from common table salt (NaCl). The general characteristics of Halogens also include having a relatively weak intermolecular force, and when reacted with atoms, they gain an electron.

Compounds of Halogens

Other than the characteristics of Halogens that we have discussed above, like their reactivity, there are a few different reactions that form compounds of Halogens.

There are two types of halides: one is hydrogen halides and the other is metal halides.

Hydrogen Halides – this Halogen compound is acid in aqueous form and is diatomic and inorganic. This functions as Arrhenius acids, and the formula is HX, where X is one of the Halogens of the Group 17 elements (Fluorine, Chlorine, Bromine, Iodine, or statine) and are in gaseous form at standard pressure and temperature and do not tend to ionise in this form. This is why chemists differentiate a hydrogen chloride from hydrochloric acid, wherein the former is in a gaseous state at room temperature and is reactive to water and forms acid. It is difficult to regenerate the diatomic molecule once it has turned into acid.

Metal Halides – metal halides tend to have a very high boiling and melting point and freely dissolve in water, while some are deliquescent and do not solute well with organic solvents. The metal halides that dissolve in water are ferrous chloride, cupric chloride, and nickelous chloride and are low-oxidation state transitions. Although these metals have high boiling and melting point, these are still lower than ionic metal halides, unlike having higher than monomeric metal halides.

PolyHalogenated – also known as PHCs, have multiple substitutions of Halogens and bioaccumulate in humans as these belong to a group of several carcinogenic and toxic chemicals used in industries. These are used in making materials for automobiles, clothes, paints, pesticides, etc., and are notoriously dangerous, even the non-pesticide ones. Although there have been efforts to minimise the amount of PHCs that come in contact with humans, it cannot be prevented to a great extent. For this reason, anaerobic bacteria are used during manufacture to reduce the amount of PHCs.

InterHalogens – the interHalogen bonds are more reactive than diatomic bonds. Thus, they get converted to Halide and Oxyhalide ions as they are weaker than diatomic bonds except for F₂ while being explosive if reacted with BrF₅. For producing larger interHalogens such as CIF₃, the smaller interHalogens like CIF are exposed to pure diatomic Halogens, F₂, which help generate Halogen Fluoride. InterHalogens are created when two pure Halogens are combined under different conditions, which can also generate any interHalogen save for IF₇.

Conclusion

In the above paragraphs, we have answered the fundamental question – what are Halogens? Halogens are the six elements on the periodic table that together form a group called Group 17 as they have some unique characteristics compared to other elements on the table. These Halogens are highly reactive and cause physical and chemical changes within the elements and their atomic structure. These are more reactive than any other elements because of which these are used for several purposes like pesticides, disinfectants, in industries, etc., and bioaccumulate, which means these are harmful to the living organisms. Measures have been taken to reduce the number of Halogen compounds that flow into the ecosystem. However, our dependency on these elements for various purposes is still a long way from being at a safe distance.