1) The shapes of molecules are determined by electron pair repulsion theory (VSEPR), which predicts molecular geometry based on the number of electron pairs around a central atom. 2) Electron pairs repel one another, seeking positions as far apart as possible to minimize repulsion. The greatest repulsions are between lone pairs, followed by lone pairs and bond pairs, with the weakest being between bond pairs. 3) Common molecular geometries predicted by VSEPR include tetrahedral for 4 electron pairs, trigonal planar for 3 pairs, and linear for 2 pairs. Deviations from the ideal angles can occur due to unequal repulsions between different types of electron pairs.