Walsh applied his approach to molecules other than compounds of hydrogen, but the correlation diagrams soon become very complicated. His a roach re resents a valuable i PP P complement to the VSEPR model because it traces the influences on molecular shapes of the occupation of orbitals spreading over the entire molecule and concentrates less on localized repulsions between pairs of electrons. Correlation diagrams like those introduced i by Walsh are frequently encountered in contemporary discussions of the shapes of g complex molecules, and we shall see a number of examples in later chapters. They a illustrate how inorganic chemists can sometimes identify-andweigh competing influences by considering two extreme cases (such as linear and 90° XHQ molecules), and then rationalize the fact that the state of a molecule is a compromise intermediate between the two extremes. In the Walsh model the shape ofa molecule is predicted on the basis ofthe occupation of molecular orbitals that, in a correlation diagram, show a strong dependence on bond angle.