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An oxyacid, also known as an oxoacid or ternary acid, is an acid-containing oxygen. It contains oxygen, hydrogen, and at least one other element, with at least one hydrogen atom bound to oxygen. An oxyacid is capable of dissociating to create an H+ cation and anion.

What are Oxoacids? 

  • When an acid contains oxygen (an oxoacid), the suffixes –ous and –ic are used to signify the lower and higher number of oxygens in the acid formula, respectively. 
  • Oxoacids are acids that contain hydrogen, oxygen, and another element.

Halogens

  • Fluorine, chlorine, bromine, iodine, and astatine are all members of Group 17. They’re known as halogens or salt producers.
  • Oxides are formed by the complete halogen family. Although many halogen oxides have been discovered, the majority of them are unstable. Because halogens and oxygen have similar electronegativity, halogen-oxygen bonds are extremely covalent. 
  • Because fluorine is more electronegative than oxygen, fluorine-oxygen compounds are referred to as fluorides of oxygen rather than fluorides of fluorine. As we progress down the group, the physical and chemical properties positively change.
  • Astatine is the group’s only radioactive element. In their valence shell (ns2np5), they have seven electrons, one less than the nearest noble gas configuration. 

Oxoacids of Halogens

  • Several oxoacids are formed by halogens (they are acids that contain oxygen in the acidic group).
  • The only halogen oxide that is stable (with respect to dissociation into elements) is I2O5.
  • The thermal stability of halogens decreases as the atomic number of the halogen increases. As a result, among the hypohalous acids, HOCl is the most stable, whereas HOI is the least stable. 
  • The terminal oxygen atom pulls the electrons of the O-X bond towards itself since oxygen is more electronegative than halogens (Cl, Br, and I), leaving a small positive charge on the halogen atom. The halogen atom then attracts the X-OH bond’s electrons to itself, making the O-H bond more easily ionisable.
  • As we move down the group, the acid strength of oxoacids with halogen in a similar oxidation state decreases.

Preparation of Halogen Oxides

  • Fluorine is dissolved in a 2 percent NaOH solution to produce oxygen difluoride:

2F2 + 2NaOH → 2NaF + H2O + OF2

  • It is a colourless, stable gas. It produces fluorides and oxides when it reacts strongly with metals, halogens, sulphur, phosphorus, etc. It produces F– ion and free oxygen when it combines with bases.
  • Cl2O and Br2O are made up by heating freshly precipitated mercuric oxide.

2X2 + 2HgO → HgX2·HgO + X2O, where X = Cl/Br (at 573 K)

Properties of Halogen oxoacid

  1. They are unable to be isolated in their natural state. In aqueous solution or in the form of salts, they are stable. Hypohalous acids (+1 oxidation state), halous acids (+3 oxidation state), halic acids (+5 oxidation state), and perhalic acids (+7 oxidation state) are the four types of oxoacids formed by halogens.
  1. Chlorine produces four different types of oxoacids. HOClO2 (chloric acid), HOCl (hypochlorous acid), HOClO (chlorous acid), and HOClO3 (perchloric acid).
  1. HOBr (hypobromous acid), HOBrO2 (bromic acid), and HOBrO3 (hypobromous acid) are the three forms of bromine (perbromic acid). HOI (hypoiodous acid), HOIO2 (iodic acid), and HOIO3 (hypoiodic acid) are all forms of iodine (periodic acid).

Structures of the Oxoacids of Halogens

  1. Each oxoacid contains an X-OH bond. “X = O” bonds are available in the majority of these oxoacids. Hypofluorous acid, hypochlorous acid, hypobromous acid, and hypoiodous acid are all hypohalous acids. In hypohalous acids, the halogen has an oxidation state of +1.
  2. The structures of OF2, Cl2O, Br2O, Cl2O7, and I2O5 are the only ones that are certain. The VSEPR theory can be used to depict the structures of monoxides. These oxides have a tetrahedral structure with two oxygen lone pairs. As a result, the molecule has a ‘V’ or angular form. In the order FOF ClOCl BrOBr, the bond angle EOE varies.

Conclusion

Oxyacids are chemicals that contain halogen atoms and oxygen atoms. F, Cl, Br, I, and astatine make up group 17. As the last differentiating electron enters the p orbital of the n shell, these are p-block elements. These are the non-metallic elements that are the most reactive. Astatine, the family’s last member, is a radioactive (short-lived) substance (artificially prepared).