Contribution of the shape factor sigma(r) to atomic and molecular electronegativities

The contribution of the shape factor sigma(r) to the electronegativity is established. This shape factor, measuring the shape of the electron density rho(r), is defined as sigma(r) = rho(r)/N and integrates to unity: integral sigma(r) dr = 1. A new response function is thereby introduced, giving the change of the energy of an atomic or molecular system with respect to the shape factor sigma(r). Finally, a physical interpretation is given for this response function.