The H Ion in Water

The first ionization energy of H atom (1311kJmoU ) is very high in comparison with that of many other elements, such as alkali metals. Removal of the Is electron leaves a bare proton, which, having a radius of only about 1.5 x 10 pm, never exists in the condensed phase. However, when bonded to other species it is well known in solutions and in solids (e.g. H3O+, NH4+, etc.). The proton affinity of water and the solvation energy of the H+ ion in water have been estimated... 

Compounds that furnish solvated H+ ions in snitable polar solvents, snch as water, are protonic acids. The natnre of the H+ ions in water, which should more correctly be called the hydroxonium ion, H3O+, is customarily referred to as the hydrogen ion . 

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