Seesaw shape

Because equatorial and axial positions differ, two molecular geometries are possible for SF4. As Figure 9-22 shows, placing the lone pair in an axial position gives a trigonal pyramid, whereas placing the lone pair in an equatorial position gives a seesaw shape. 

SF4 seesaw shape and polar SiF4 tetrahedral shape and non-polar... 

SF4 4 S-F bonds, leaving 2 electrons or 1 lone pair. SF4E trigonal bipyramid with E in one equatorial position. The 4 S-F bonds bend away from the E, giving a seesaw-shaped molecule. 

In (a) the lone pair occupies an equatorial position, and in (b) it occupies an axial position. The axial position has three neighboring pairs at 90° and one at 180°, while the equatorial position has two neighboring pairs at 90° and two more at 120°. The repulsion is smaller for (a), and indeed (a) is the structure observed experimentally. This shape is sometimes described as a distorted tetrahedron (or a folded square, or seesaw shape). The angle between the axial F atoms and S is 186°, and that between the equatorial F atoms and S is 116°. 

From which of the fundamental geometries shown in Figure 9.3 could you remove one or more atoms to create a molecule having this seesaw shape [Section 9.1 ]... 

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 sulfur has five electron domains around it four from 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 wUl point toward an equatorial position. The four bonds point toward the remaining four positions, resulting in a molecular geometry that is described as seesaw-shaped ... 

All bonding groups octahedral shape (AXg). When seesaw-shaped SF4 (discussed above) reacts with more F2, the central S atom expands its valence shell further to form octahedral sulfur hexafluoride (SFg) ... 

Practice Problem B For which molecular geometries (linear, bent, trigonal planar, trigonal pyramidal, tetrahedral, square planar, T-shaped, seesaw-shaped, trigonal bipyramidal, square pyramidal, octahedral) can an AB, molecule be nonpolar if there are (a) two drflerent types of terminal atoms and (b) three different types of terminal atoms ... 

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