Five Electron Groups with Lone Pairs

Five Electron Groups with Lone Pairs 

I The seesaw molecular geometry Is sometimes I called an irregular tetrahedron. 

Three 90° lone pair-bonding pair repulsions 

When three of the five electron groups around the central atom are lone pairs, as in Xep2, the lone pairs occupy all three of the equatorial positions, and the resulting molecular geometry is linear. 

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Five Electron Groups with Lone Pairs... 

When the nitrogen atom of the amide belongs to an azole (aromatic five-membered ring) the lone pair is less available to conjugate with the carbonyl group because it is part of the aromatic sextet [33], In some way the barrier in azolides (18) is an indirect measure of the aromaticity of the azole, or more precisely of the ability of the N1 lone pair to share its electrons. The calculated and experimental values of a series of barriers of azolides are reported in Table 1 [34],... 

Ligands with lone pairs such as R, R2N, X, and O groups can use their lone pairs to make 77 bonds to the metal, as in M OR <—> M=OR. (Again, formal charges are usually not drawn.) Thus, these groups can be three- (R, R2N, X), four-(O), or even five-electron donors (RO, X), if the metal needs the extra electron density and it has orbitals of the right symmetry to overlap with the donor orbitals. 

For the trigonal bipyramidal shape of the PCI5 molecule, for example, the VB model proposes that the one 35, the three 3p, and one of the five 3d orbitals of the central P atom mix and form five sp d hybrid orbitals, which point to the vertices of a trigonal bipyramid (Figure 11.6). Seesaw, T-shaped, and linear molecules have this electron-group arrangement with lone pairs in one, two, or three of the central atom s sp d orbitals, respectively. 

When there are five electron groups around the central atom, it is sp d hybridized. AB5 molecules and ions with no lone pairs on the central atom have trigonal bipyramidal electronic geometry, trigonal bipyramidal molecular geometry, and sp d hybridization on the central atom. 

The central atom, S, is bonded to four atoms and has one lone pair. This is an example of the general formula AB4U. Sulfur has five electron groups, so we know that the electronic geometry is trigonal bipyramidal and the bonding orbitals are sp d hybrids. But now a new question arises Is the arrangement more stable with the lone pair in an axial (a) or in an equatorial (e) position If it were in an axial position, it would be 90° from the three closest... 

Five electron-group arrangements are possible when two, three, four, five, or six electron groups surround a central atom. Each arrangement is associated with one or more molecular shapes, depending on the numbers of bonding and lone pairs. 

Which molecule geometry results when a central atom has five total electron groups, with three of those being bonding groups and two being lone pairs ... 

With a steric number of 5, chlorine has trigonal bipyramidal electron group geomehy. This means the inner atom requires five directional orbitals, which are provided hymsp d hybrid set. Fluorine uses its valence 2 p orbitals to form bonds by overlapping with the hybrid orbitals on the chlorine atom. Remember that the trigonal bipyramid has nonequivalent axial and equatorial sites. As we describe in Chapter 9, lone pairs always occupy equatorial positions. See the orbital overlap view on the next page. 

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