A metal ion in aqueous solution or aqua ion is a cation, dissolved in water, of chemical formula [M(H2O)n]z+. The solvation number, n, determined by a variety of experimental methods is 4 for Li+ and Be2+ and 6 for elements in periods 3 and 4 of the periodic table. Lanthanide and actinide aqua ions have a solvation number of 8 or 9. The strength of the bonds between the metal ion and water molecules in the primary solvation shell increases with the electrical charge, z, on the metal ion and decreases as its ionic radius, r, increases. Aqua ions are subject to hydrolysis.
A metal ion is a type of atom compound that has an electric charge. Such atoms willingly lose electrons in order to build positive ions called cations. Ions are essentially enclosed by delocalized electrons which are responsible for processes like conductivity. The logarithm of the first hydrolysis constant is proportional to z2/r for most aqua ions. Metal aqua ions are complexes composed of a metal cation coordinated to six water molecules (except in the case of copper, but that’s another topic). You will often see aqueous metal cations written as M+2 (aq) and M+3 (aq). Because water can function as a Lewis base and transition metal ions can function as Lewis acids, most salts containing transition metals form coordination complexes when they are dissolved in water.
The aqua ion is associated, through hydrogen bonding with other water molecules in a secondary solvation shell. A metal ion is a type of atom compound that has an electric charge. Such atoms willingly lose electrons in order to build positive ions called cations. Ions are essentially enclosed by delocalized electrons which are responsible for processes like conductivity. The solvent molecules (water in this case) surround the ions removing them from the crystal and forming the solution. As the dissolving process proceeds, the individual ions are removed from the solid surface becoming completely separate, hydrated species in the solution. Water molecules in the first hydration shell exchange with molecules in the second solvation shell and molecules in the bulk liquid. The residence time of a molecule in the first shell varies among the chemical elements from about 100 picoseconds to more than 200 years. Aqua ions are prominent in electrochemistry. In general, a substance will be insoluble if the energy expended to break apart the solvent and solute particles is significantly greater than the energy given off when solute-solvent interactions are established.
