Equatorial electron domains

Fig. 30 A—C. The Berry mechanism for electron-pair-coordination-number 5. (A) Trigonal bipyramidal coordination. Ligands bonded through shaded electron-domains are in axial positions. (B) Tetragonal pyramidal coordination. A slight distortion of structure A. (C) Trigonal bipyramidal coordination. A slight distortion of structure B. Ligands bonded through shaded electron-domains are now in equatorial positions...

The sulfur has five electron domains around it four fiom the S — F bonds and one from the nonbonding pair. Each domain points toward a vertex of a trigonal bipyramid The domain from the nonbonding pair will point toward an equatorial position. The four bonds point toward the remaining four positions, resulting in a molecular geometry that is described as seesawshaped ... 

Removing an atom from the equatorial plane of the trigonal bipyramid in Figure 9.3 creates a seesaw shape. 93 (a) 2 electron-domain geometries, linear and trigonal bipyramidal (b) 1 electron-domain... 

The trigonal bipyramidal electron geometry for five electron domains. The three equatorial (eq) positions lie in a trigonal plane along the equator of the molecule, whereas the two axial (ax) domains lie along the vertical axis of the molecule. [E. Generalic,... 

Lastly, the BrF3 molecule has five electron domains, predicting a trigonal bipyramidal electron geometry. The two lone-pair domains will occupy more space around the central Br atom than will the shared Br-F single-bond domains. The lone pairs will therefore prefer two of the equatorial sites in the trigonal... 

This theory can also be applied to molecules and ions that have five and six electron domains. The basic shapes (Figure 14-1) adopted by molecules with five or six electron pairs are trigonal bipyramidal and octahedral, respectively. These shapes minimize the repulsion between electron pairs in the valence shell. The trigonal bipyramid has three equatorial bonds and two axial bonds the octahedron has six equivalent bonds. 

For species with five electron domains there are alternative positions for any lone pairs of electrons. The favoured positions will be those where the lone pairs are located furthest apart, thus minimizing the repulsive forces in the molecule. Consequently, lone pairs will usiuxlly occupy equatorial positions. 

The valence shell of the sulfur atom contains ten electrons six from the sulfur and one each from the four fluorine atoms. There are four bonding pairs and one lone pair. The basic shape adopted by the electron pairs In the molecule Is trigonal bipyramidal. In this arrangement, the electron pairs at the equatorial positions experience less repulsion compared to axial electron pairs. Flence the lone pair occupies an equatorial position and thus the shape of the molecule Itself resembles a see-saw (Figure 14.5). As a general rule, for a molecule where the electron domains adopt a trigonal bipyramidal structure, any lone pairs will occupy equatorial positions. 

With five identical electron domains around the central atom, the electron-domain and molecular geometries are trigonal bipyramidal. The equatorial bond dipoles will cancel one another, just as in the case of BF3, and the axial bond dipoles will also cancel each other. 

Delocalized. 352 Diamagnetic, 342 Electron domain, 314 Electrcn-domain geometry, 316 Equatorial, 316 Hybridization, 327... 

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