The data obtained show that at pH 7 copper(II) ions are adsorbed on a SiO2 surface as polymeric species of hydroxide nature. The structure of these species is similar to that of the bulk amorphous copper hydroxide, The amorphous state of supported Cu(OH)(2) is caused by a small (ca. 11 Angstrom) size of the surface particles. In contrast, the overstoicheometric water molecules seem to act as "amorphizers" of the bulk copper hydroxide. The structures of the bulk and dispersed amorphous copper(IT) hydroxide were determined. The amorphous Cu(OH)(2) has a layered structure close to the structure of the crystalline hydroxide, but the layers in the amorphous hydroxide are shifted toward one another approximately for 1/4 of the "c" period of the lattice,