Chemistry · Ch 14 — The p-Block Elements
Oxoacids of Halogens
Oxoacids of Halogens
Oxoacids of the Halogens
Because of its high electronegativity and small atomic size, fluorine forms only a single oxoacid: HOF, known as fluoric(I) acid or hypofluorous acid. The other three common halogens, by contrast, form a whole family of oxoacids — though most of these cannot be isolated as pure compounds and exist only in aqueous solution or as their salts.
The oxoacids of the halogens, organised by oxidation state, are:
| Acid type (oxidation state) | F | Cl | Br | I |
|---|---|---|---|---|
| Halic(I) acid — Hypohalous acid | HOF (hypofluorous acid) | HOCl (hypochlorous acid) | HOBr (hypobromous acid) | HOI (hypoiodous acid) |
| Halic(III) acid — Halous acid | – | HOClO (chlorous acid) | – | – |
| Halic(V) acid — Halic acid | – | HOClO₂ (chloric acid) | HOBrO₂ (bromic acid) | HOIO₂ (iodic acid) |
| Halic(VII) acid — Perhalic acid | – | HOClO₃ (perchloric acid) | HOBrO₃ (perbromic acid) | HOIO₃ (periodic acid) |
Reading down a column traces chlorine's, bromine's or iodine's oxoacids through increasing oxidation state; reading across the table shows just how few of these acids fluorine is able to form, compared with the fuller family available to the heavier, less electronegative halogens. …
| Halic (I) acid (Hypohalous acid) | HOF (Hypofluorous acid) | HOCl (Hypochlorous acid) | HOBr (Hypobromous acid) | HOI (Hypoiodous acid) |
|---|---|---|---|---|
| Halic (III) acid (Halous acid) | - | HOClO (chlorous acid) | - | - |
| Halic (V) acid (Halic acid) | - | HOClO2 (chloric acid) | HOBrO2 (bromic acid) | HOIO2 (iodic acid) |
What this figure shows. Four ball-and-stick molecular structure diagrams in a horizontal row (p.205), each drawn with purple/lavender spheres for atoms (labelled H, O, Cl) joined by bond lines (double lines for double bonds), with a name printed below each structure. (1) 'Hypochlorous acid' (leftmost): a bent 3-atom unit with O at the apex/top, connected by a single bond down-left to H and a single bond down-right to Cl — angular V-shape, no double bonds. (2) 'Chlorous acid': H at far left bonded by a single bond to an O; that O is single-bonded to a central Cl positioned lower-right; the Cl is also double-bonded (double line) to a second O placed to the upper-right of Cl — so Cl has one single-bonded (OH) oxygen and one double-bonded oxygen. (3) 'Chloric acid': H at the top bonded down by a single bond to an O; that O is single-bonded down to a central Cl; the Cl is additionally double-bonded to two more O atoms, one positioned to the left of Cl and one positioned below Cl — so Cl has one single-bonded (OH) oxygen plus two double-bonded oxygens, three O neighbours total arranged around Cl. (4) 'Perchloric acid' (rightmost): H at the top bonded down by a single bond to an O; that O is single-bonded down to a central Cl; the Cl is additionally double-bonded to three more O atoms positioned left, right and below Cl — so Cl has one single-bonded (OH) oxygen plus three double-bonded oxygens, four O neighbours total arranged roughly tetrahedrally around the central Cl. Reading left to right the number of terminal …