The signal intensity monitored in surface-sensitive electron spectroscopies is frequently simulated using Monte Carlo algorithms. Elastic interactions of electrons with atoms in the solid are usually described using differential elastic-scattering cross sections calculated for isolated neutral atoms. In reality, the interaction of an electron with bound atoms should be different than the interaction with isolated atoms. In the present paper, we study the effect of atomic aggregation on calculated elastic electron backscattering probabilities. It has been found that the differential elastic scattering cross-section is strongly affected in the region of small scattering angles; the cross sections for isolated atoms are larger, by a factor of up to five than the cross section obtained with a muffin-tin model potential simulating the solid. However, the elastic backscattering probability resulting from the Monte Carlo simulations is affected very weakly by the change of the cross section. At energies of 500 and 1000 eV, the mean percentage difference is comparable with the statistical uncertainty of the Monte Carlo calculations. The results obtained here support the use of the elastic scattering cross sections for free atoms in theoretical models and calculations of electron transport in the surface region of solids.