What Are Halogens?
Halogen is a term that was derived from the Greek word ‘halo’ which means salt and ‘gen’ meaning producer. The term halogen therefore means salt producer. This is because they produce a wide range of salts when they react with metals. The name halogen was first proposed by a German chemist by the name Johann Schweigger in 1881 Examples of halogens include substances such as fluorine (F), chlorine (Cl), bromine (Br), iodine (I) astatine (At) and tennessine (Ts). The names of all these elements were derived from Greek words with the exception of tennessine which is named after Tennessee, a state in the US. Fluorine is the most abundant of all the halogens in the earth’s surface.
Properties of Halogens
Physical Properties of Halogens
Halogens are generally non-metals belonging to Group VII of the periodic table. The modern IUPAC nomenclature places these chemically related elements in group 17. Halogens are non conductors of heat and electricity because there are no delocalized electrons in their structures
They have seven electrons in the outer energy level. The atomic and ionic radius of the halogens increases down the group because there is an increase in the number of occupied energy levels. However, the atomic radius of a halogen atom is less than the radius of its ion. This is due to the repulsive effect that exists between the existing electrons and the incoming electron resulting in the outer electrons moving further causing an increase in the size of the ion.
When it comes to appearance, fluorine is pale yellow in color, chlorine is greenish-yellow or pale green in color, bromine has a dark reddish-brown appearance while iodine has a shinny purple appearance when in solid form and forms a very dark violet appearance when it’s melted. Very little is known about the artificially produced tennessine element.
Fluorine and chlorine exist as gases at room temperature. Iodine and astatine are solids at room temperature while bromine is a liquid. Astatine is believed to be dark to black in color.
Halogens such as Fluorine are generally insoluble in water. Chlorine, bromine and iodine are slightly soluble in water since water is polar while these halogens are non-polar. Water molecules have stronger intra-molecular forces whereas halogens have weak Vander Waals forces. All halogens are soluble in tetrachloromethane. Solubility of halogens decreases down the group. Chlorine for example, is more soluble in water than bromine and iodine. All halogens are more soluble in non-polar solvents than in water.
When heated, iodine sublimes to form a purple vapor mainly because its particles are held by weak forces which require little energy to break. The melting and boiling point of halogens increases down the group since their molecular size increases and more heat will be required to overcome the strong Vander Waals forces.
The density of halogens increases down the group due to an increase in atomic mass.
Chemical Properties of Halogens
Halogens react by gaining one electron to attain a stable electron configuration and form negatively charged ions (halides). This is because they require very little amount of energy to gain an electron than to lose electrons. This oxidizing ability decreases down the group as the electron affinity decreases. Fluorine is therefore the stronger oxidizing agent in the group due to its low bond energy.
Halogens are highly reactive due to their high electronegativity. Their electron affinity decreases down the group as the size of the atoms increases. Reactivity of halogens decreases down the group because of this. As such, fluorine is the most reactive of all the halogens. It is commonly handled using Teflon since it is highly resistant to thermal and chemical attacks. Other substances used to handle it include dry glass and metals such as steel and copper.
They react with hydrogen to for hydrogen halides such as hydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodide and hydrogen astatide. Hydrogen halides are usually colorless gases at room temperature and dissolve in water to form acids. These acids include; hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid and hydroastatic acid.
A reaction between halogens and metals results in the formation of salt or metal halides such as ferric chloride, sodium chloride, zinc bromide and zinc iodide.
A displacement reaction occurs when a more reactive halogen is placed into a solution containing a less reactive halide. For example, fluorine would displace halides belonging to the halogens.
Use of Halogens
Fluorine is a raw material in the preparation of synthetic fiber known as polytetraflouroethene. This material is used to make non-stick cookware, as a lubricant, making anti corrosive containers and pipes as well as making insulators.
Some compounds of fluorine are added to water and toothpaste in small quantities to reduce tooth decay.
Fluorine is also used to manufacture hydrogen fluoride used to engrave words and photographs in glass. In addition to this, fluorine is used to make hydrofluoric acid used in glass etching.
Bromine and chlorine are used as disinfectants for wounds, drinking water, dishes and dishes and various surfaces. This is due to their ability to kill bacteria and other harmful microorganisms. It is also used in the manufacture of silver bromide used to make the light sensitive photographic paper and film.
Chlorine is used in the manufacture of hydrochloric acid, common salt and bleaches. In addition to that, chlorine is used in the manufacture of polyvinylchloride (PVC).
Iodine is used as an antiseptic due to its ability to kill fungus, bacteria and other microorganisms. It also plays a crucial role in the function of thyroid glands. A deficiency in iodine leads to hypothyroidism. Iodine can be combined with potassium to treat radiation exposure.