Octahedral electronic geometry

This polyatomic ion (type AB6), like (c), does not obey the octet rule without modification since 12 electrons must be shared to form 6 Sb-F bonds. Sb is a 5 A element, but the charge on the ion gives an extra electron which participates in bonding. The Lewis formula predicts 6 electron groups around the central Sb atom and an octahedral electronic geometry. There are no lone pairs on the Sb atom, so the ionic geometry is the same as the electronic geometry (Section 8-12). 

By similar reasoning, VSEPR theory predicts octahedral electronic geometry and octahedral molecular geometry for the PFg ion, which has six valence shell electron pairs and six F atoms surrounding one P atom. 

D. Unshared Valence Electron Pairs in Octahedral Electronic Geometry... 

If the Lewis formula for a molecule or ion shows only one lone pair In Unear, trigonal planar, tetrahedral, or octahedral electronic geometry, all positions are equivalent, so it doesn t matter where we place the lone pair. In trigonal bipyramidal electronic geometry, place the lone pair in the equatorial position where it is least crowded, and put the bonded atoms in the other positions. 

Figure 8-3 Arrangements of bonded atoms and lone pairs (six regions of high electron density—octahedral electronic geometry).

When there are six electron domains around a central atom, the lowest energy configuration is an octahedron. In the octahedral electron geometry, there are four domains that lie in a square plane that is perpendicular to the paper at 90° angles from one another, whereas the two other domains are equidistant above and below the plane and at a 90° angle. Thus, all six sites in the octahedral geometry are equivalent by symmetry and there will be no special preferences for any particular site. 

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

The xenon atom has six electron groups and therefore has an octahedral electron geometry. An octahedral electron geometry corresponds to hybridization (refer to Table 10.3). 

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