The elements found in Group 17 of the Periodic Table are collectively known as the halogens. This family of non-metallic elements includes fluorine, chlorine, bromine, and iodine, all characterized by their intense chemical reactivity. Their strong tendency to combine with other substances is a direct result of their placement in the periodic structure.
The Origin of the Name Salt Former
The designation “halogen” is rooted in two ancient Greek terms that describe the elements’ primary chemical function. The first component is hals, which translates to “salt” or “sea,” referencing the abundance of their compounds in seawater and mineral deposits. The second part, -gen, means “to form” or “to generate,” a suffix often used in chemistry to denote a producer of a substance.
Combining these roots, the name literally signifies a “salt former” or “salt producer.” This descriptor was chosen because the elements readily react with metals to create compounds with properties similar to common table salt. The term was first proposed in 1811 by the German chemist Johann Schweigger.
The functional concept gained widespread use starting in 1826, championed by the influential Swedish chemist Jöns Jacob Berzelius. Berzelius applied the term to the group of elements that included fluorine, chlorine, and iodine. He recognized that these elements consistently produced a sea-salt-like substance when they formed a compound with an alkaline metal. This consistent chemical behavior across the family justified applying the name to the entire group.
Defining the Halogen Family
The elements of the halogen family reside in Group 17 of the periodic table, situated immediately adjacent to the noble gases. Their unique chemical behavior is defined by their electron configuration, as all halogens possess seven valence electrons in their outermost shell. This arrangement leaves them just one electron short of achieving the highly stable, full octet configuration of a noble gas.
This electronic deficiency drives their extreme reactivity, making them powerful oxidizing agents ready to accept an electron from other atoms. Fluorine, in particular, is the most electronegative of all elements, meaning it has the strongest pull for an electron to complete its shell.
The halogen family includes six elements:
- Fluorine (F)
- Chlorine (Cl)
- Bromine (Br)
- Iodine (I)
- Astatine (At), a highly rare and intensely radioactive element
- Tennessine (Ts), a synthetic element whose chemical properties are still largely unknown
The physical states of these elements at standard temperature illustrate a clear trend moving down the group. Fluorine is a pale yellow gas, and chlorine is a distinctly yellow-green gas. Bromine exists as a dark red-brown liquid, while iodine is a lustrous purple-black solid that easily sublimes into a purple vapor. This progression from gas to liquid to solid correlates directly with increasing atomic size and the strength of the intermolecular forces.
Common Everyday Halide Salts
Halogen compounds are known chemically as halide salts. A halide is a compound formed when a halogen atom bonds with a less electronegative element, typically a metal, by gaining an electron to form a negatively charged halide ion.
The most widely recognized example is sodium chloride (NaCl), which is the common table salt used for seasoning and food preservation. This compound is formed by the direct reaction between the metal sodium and the halogen chlorine. The natural mineral form of this salt, called halite, is mined extensively around the globe.
Halide salts are incorporated into many everyday products:
- Potassium chloride (KCl) is used as a salt substitute in foods and as a component in agricultural fertilizers.
- Sodium fluoride (NaF) is routinely added to municipal water supplies and toothpaste formulations to help prevent dental decay.
- Silver bromide (AgBr) and silver iodide (AgI) were historically used in photographic film due to their light-sensitive properties.
- Magnesium chloride (MgCl2) is used widely in de-icing treatments on roads and sidewalks due to its ability to effectively lower the freezing point of water.