# What is the "acidium species" in water?

Because ${H}^{+}$ is a conception, as is ${H}_{3} {O}^{+}$. The actual species (as far as anyone knows) is a cluster of water molecules ${\left(O {H}_{2}\right)}_{n}$, with an extra ${H}^{+}$, to give ${\left({O}_{n} {H}_{2 n + 1}\right)}^{+}$.
Water molecules are exceptionally proton dense (and also dense in terms of molecules); the charge can pass from molecule to molecule in the cluster rather than an actual proton; in a sense this is proton tunneling. The same type of charge transfer can occur with the hydroxide ion, $O {H}^{-}$. If you have ever played rugby, consider a maul, where the forwards pass the pill from hand to hand while moving forward (and here the ball is the extra ${H}^{+}$; of course rugby is a macroscopic phenomenon).