In this Letter Quantum Similarity for Atoms (H-Xe) is investigated using electron densities and shape functions, looking for patterns of periodicity as in Mendeleev's Table. An LS-dependent restricted Hartree-Fock method is used to obtain the wave functions from which the electron densities are calculated. Utilizing the quantum similarity proposed by Carbo a nearest neighbour dominated similarity is retrieved, masking periodicity. Introduction of the information discrimination concept with reference to the noble gas atom of the previous row is found to reveal periodicity, with improved results when densities are replaced by shape functions throughout. This confirms recent literature on the fundamental role of the shape function as carrier of information. (C) 2004 Elsevier B.V. All rights reserved.