We obtained a chemotopological classification of the 17 fourth period monohydrides based on their B3LYP/6-311+G(3df,3pd) properties. This classification has a chemical plentiful sense and it is similar to that of Rayner-Canham, based on experimental data. The topological properties of ionic, metallic and covalent subsets of these hydrides show that the ionic and the covalent subsets are robust subsets since their closures and interiors are the same sets. Moreover, the fact of using topology opens the way for classifications of other compounds. On the other hand, we found that the 6-311+G(3df,3pd) basis set produces bond lengths and harmonic frequencies in agreement with the experimental values for transition-metal and main-group monohydrides. (c) 2006 Elsevier B.V. All rights reserved.