A quantum chemical analysis of interaction of impurity and alloying elements with grain surface in iron is carried out. The elements of the first five periods (from hydrogen to xenon) are considered. The cluster and slab models are used. Within these models the boundary between grains is imitated by a multilayered system including atoms of two neighboring grains of iron and a layer of the impurity (alloying) atoms between them. Grain surfaces with the Miller indices (100) and (110) are considered. The energy needed for disintegration (decohesion) of the system into two parts is determined. It is shown that dependence of decohesion energy of the system on atomic number of the impurity (alloying) atoms is of the same type for different models. It testifies to opportunity of studying such dependence by means of simple models and carrying out on this basis a classification of elements based on their ability to strengthen grain boundaries. The produced estimates of compatibility of the elements with iron on grain boundaries in steel agree with the known experimental data and correspond to Mendeleev’s periodic law. Possibilities of diffusion introduction of the strengthening elements into steel surface layers with a view to increase their wear resistance are discussed. The discovered dependences can be used for the prediction of wear resistance and strength properties of polycrystalline materials with various alloying additives.