Since electrons repel one another, Fermi holes and Fermi heaps have drastic effects on the energy of many-electron atoms, such as the periodic properties of the elements. Since bringing electrons together requires doing work, Fermi heaps have higher energy than Fermi holes. This result is generalized in terms of multiplicity by Hund's rule which states that the higher the spin multiplicity of a state (number of spin states it is allowed to have by the exclusion principle), the lower its energy will be.