oxoacid

Many of the most important inorganic acids are built around a central atom wearing oxygen atoms, with the acidic hydrogens hanging off some of those oxygens. Nitric acid, sulfuric acid, phosphoric acid, perchloric acid, carbonic acid — these are oxoacids: acids of the general form (HO)mEOn, where E is a central atom (often a nonmetal or a high-oxidation-state metal), some oxygens carry an OH (the acidic protons), and the rest are terminal, double-bonded-style E=O oxygens.

Sulfuric acid, H2SO4, makes the pattern concrete. The sulfur sits at the center; two oxygens are terminal (S=O), and two are hydroxyl oxygens (S-OH), and it is those OH protons that ionize in water. Writing it as (HO)2SO2 with m=2 OH groups and n=2 terminal oxygens captures this. The acidic proton is never bonded directly to the central atom in a true oxoacid — it sits on an oxygen, and the O-H bond is what breaks. The more terminal O atoms, the more the negative charge of the conjugate base can spread out, and the easier the proton leaves.

Oxoacids dominate the descriptive chemistry of the p-block. Their strengths span an enormous range, from very weak (boric acid, hypochlorous acid) to extremely strong (perchloric acid), and the trend is so regular that Pauling captured it in two simple counting rules. They also come in families differing by oxidation state of the central atom — chlorine alone gives HOCl, HOClO, HOClO2, and HOClO3 (hypochlorous to perchloric), and acidity climbs sharply along that series as more oxygens are added.