Stokesian dynamics computer simulations were performed on monolayers of equally sized spheres. The influence of repulsive and attractive forces on the rheological behavior and on the microstructure were studied. Under specific conditions shear thickening could be observed in the simulations, usually together with a change in the microstructure from ordered layers to a state with large clusters. These clusters are responsible for the high viscosities in shear thickening conditions. The shear thickening results show qualitative agreement with the theoretically expected behavior and with experiments. Van der Waals forces are found to sharpen the shear thickening transitions by inducing even stronger clusters and thus higher viscosities.