Group 17 includes fluorine, chlorine, bromine, iodine, and astatine. They are collectively known as halogens, meaning salt producers. The members of this group highly resemble each other. There is a regular gradation in physical and chemical properties as we move down the group. Astatine is the only radioactive element of the group. There are seven electrons in their valence shell (ns2 np5), one electron short from the nearest noble gas configuration. Halogens have small size due to their effective nuclear charge. Hence they do not have a tendency to lose electrons, rather they readily gain an electron to complete their octet. Halogens form several oxoacids (they are acids which contain oxygen in the acidic group).
Fluorine has a very small size and high electronegativity. Therefore, it forms only one oxoacid, HOF which is known as fluoric(I) acid or hypofluorous acid. The other elements of the halogen family form several oxoacids. They cannot be isolated in the pure state. They are stable in aqueous solution or in the form of salts. Halogens generally form four series of oxoacids namely hypohalous acids (+1 oxidation state), halous acids (+3 oxidation state), halic acids (+5 oxidation state) and perhalic acids (+7 oxidation state).
Chlorine forms four types of oxoacids. That is HOCl (hypochlorous acid), HOClO (chlorous acid), HOClO2 (chloric acid) and lastly HOClO3 (perchloric acid). Bromine forms HOBr (hypobromous acid), HOBrO2 (bromic acid) and HOBrO3 (perbromic acid). Iodine forms HOI (hypoiodous acid), HOIO2 (iodic acid) and HOIO3 (periodic acid).
The central atom in the oxoacids is sp3 hybridized. Every oxoacid has essentially one X-OH bond. Whereas most oxoacids have X=O bonds present in them. This double bond between oxygen and halogen is d pi-pi in nature. In the series of oxoacids, the first member possesses high acidic strength. This is only due to high electronegativity and small size of the halogen atom. The acidic strength increases with increase in the oxidation number of halogens.
This article explains the oxoacids of halogens. For any further detail on this topic please install Byju’s the learning app.