|Fig. 1: Walsh Diagram for Molecules AB3|
Analogous to the previously presented cases it is possible to derive a Walsh diagram for molecules AB3 which is depicted in Figure 1). For these molecules, we confine ourselves to the result: The expected geometry of a molecule and the number of electrons.
|2 - 24||planar|
|25 - 27||pyramidal|
|28 - 30||planar|
Examples for planar molecules with 24 valence electrons are BF3, CO32−, NO3− and SO3. In contrast, molecules with 25 and 26 valence electrons, such as CF3, NF3, SO32− and PF3 have pyramidal molecules.
Though IF3 as a compound with 28 valence electrons is planar, note that it has not the threefold symmetry axis of D3h but belongs to point group C2v. This is a situation where the method suggested by Walsh appears inadequate. To solve this problem, we could use a threedimensional diagram were, in addition to the previously considered angles, an additional variable which represents the distortion of the threefold symmetry is introduced.
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