The Halogens and Their Properties

The elements found in group 17 of the modern periodic table are referred to as halogens. The term halogen has Greek roots (halo – salt, genes – born; halogens – salt producers). Interestingly, chlorine, bromine, and iodine formed one of Dobereiner’s Triads, a method for the classification of elements before the genesis of the periodic table of elements. The members of the halogen family include – fluorine, chlorine, bromine, iodine, astatine, and tennessine.

General Properties of Halogens

The Halogens are a highly reactive group of non-metals. They exhibit similar properties when compared to each other. However, it can be noted that astatine and tennessine are radioactive elements, whereas the rest of the halogens are not.

Halogens have the general electronic configuration of ns2np5 and contain seven electrons in their outermost shell. Due to the maximum effective nuclear charge, the halogens have the smallest atomic and ionic radii in their respective periods. However, it can be noted that the atomic radius of the elements increases down the group due to the addition of new quantum shells.

Electronegativity of Halogens

The halogens are highly electronegative. While comparing the electronegativity of different halogens, it can be observed that the electronegativity reduces down the group. It can be noted that fluorine, the first halogen, is the most electronegative element in the periodic table. Due to their high

electronegativity, halogens do not tend to lose their electrons and therefore have high ionization enthalpies. As the atomic size increases down the group, the corresponding ionization enthalpy decreases. The halogens also have highly negative electron gain enthalpies, which becomes less negative down the 17th group of the periodic table.

Due to the high electronegativity of fluorine, hydrofluoric acid acts as a weak electrolyte since the hydrogen-fluorine bond is a very strong bond. The dissociation constant of such an electrolyte can be calculated using Kohlrausch’s Law. However, hydrochloric acid is a strong acid since it ionizes completely.

To learn about the oxoacids of halogens and their properties, visit: