VSEPR model tetrahedral structures

SOLUTION The Lewis structure of nitrogen trifluoride is shown in (22) we see that the central N atom has four electron pairs. According to the VSEPR model, these four electron-rich regions adopt a tetrahedral arrangement. Because one of the pairs is a lone pair, the molecule is expected to be trigonal pyramidal (23). Spectroscopic measurements confirm this prediction. 

The VSEPR model for predicting structure does not work for complex ions. However, we can safely assume that a complex ion with a coordination number of 6 has an octahedral arrangement of ligands, and that complexes with two ligands are linear. On the other hand, complex ions with a coordination number of 4 can be either tetrahedral or square planar there is no reliable way to predict which will occur in a particular case. 

Methane, CH4, has steric number 4, and VSEPR predicts a tetrahedral structure, which is confirmed by experimental results. Starting with the electron configuration C (ls) (2s) (2p), the VB model cannot account for the formation of CH4 and predicts that CH2 would be the stable hydride, which is again contrary to the... 

The fact that the Group 14 elements form four single bonds is in agreement with the Lewis electron pair model. In these compounds the central atom is surrounded by four bonding electron pairs and the structure is tetrahedral in agreement with the VSEPR model. The observation that the E-Cl bonds in the tetrachlorides are shorter than in the dichlorides is, however, difficult to rationalize in terms of the VSEPR model. 

Water has the structure H-O-H and the VSEPR model assumes that the geometry around oxygen is roughly tetrahedral, so placing two hydrogens and two electron pairs on the oxygen leads to structure 35 for water. The VSEPR model assumes that the electron pairs are invisible, so the atoms will determine the shape. This leads to the conclusion that the H-O-H molecule is bent or angular. 

Section 8.13 molecular structure valence shell electron-pair repulsion (VSEPR) model linear structure trigonal planar structure tetrahedral structure trigonal pyramid trigonal bipyramid octahedral structure square planar structure... 

Finally, it should be noted that the XeF molecule exhibits a definite tendency to donate a fluoride ion and form the XeFj cation, which is isoelectronic and isasmic-tural with IF] as expected from the VSEFR model. The structure of solid XeF is complex, wilh 144 molecules of XeF per unit cell however there are no discrete XeF molecules. The simplest way to view the solid is as pyramidal XeF cations extensively bridged by free fluoride ions. Obviously, these bridges must contain considerably covalent character. They cause the xenon-containing fragments to duster into tetrahedral and octahedral units (Fig. 6.ISa,b). There are 24 tetrahedra and eight octahedra per unit cell, packed very efficiently as pseudospheres into a CujAu structure (Fig, 6.ISc)."-i The structure thus provides us with no information about molecular XeF, but it does reinforce the idea that the VSEPR-correct, square pyramidal XeF] is structurally stable. 

---