Planar trigonal geometry, VSEPR

Thus, the predicted bond angles in C2H4 are close to 120°, but not exactly equal to the ideal trigonal planar angle because the bonds are not all equivalent. Also, aU six of the atoms in C2H4 lie in the same plane. The planar overall geometry is not predicted by the VSEPR model, but we shall see why the molecule prefers to be planar in Section 4.3. 

Valence shell electron-pair repulsion (VSEPR) model (Section 1.10) Method for predicting the shape of a molecule based on the notion that electron pairs surrounding a central atom repel one another. Four electron pairs will arrange themselves in a tetrahedral geometry, three will assume a trigonal planar geometry, and two electron pairs will adopt a linear arrangement. 

Fig. 5. Geometries detected by TAMREAC according to the Angular Overlap and VSEPR models for four- and five-coordinate complexes. Abbreviations SPL = square planar, Td = tetrahedral, SPY = square pyramidal, TBP = trigonal bipyramidal, Is = low spin, hs = high spin, d" = number of electrons in the d configuration of the metal.

Figure 3.13 also shows the structure for CH20. Because VSEPR theory predicts a trigonal planar geometry for the double bond and the two electron pairs on the oxygen, we will treat it as spr hybridized. Again, the picture is similar to ethene, with one CO sigma bond and one CO pi bond, but with both unshared electron pairs in... 

Recall that in the VSEPR model a double bond acts as one effective pair. Thus in the ethylene molecule each carbon is surrounded by three effective pairs. This model requires a trigonal planar arrangement with bond angles of 120 degrees. What orbitals do the carbon atoms use in this molecule The molecular geometry requires a planar set of orbitals at angles of 120 degrees. Since... 

VSEPR Geometry of Domains tetrahedral tetrahedral trigonal planar... 

Cyclic compounds like benzene are not the only ones with delocalized molecular orbitals. Let s look at bonding in the carbonate ion (CO3 ). VSEPR predicts a trigonal planar geometry for the carbonate ion, like that for BF3. The planar structure of the carbonate ion can be explained by assuming that the carbon atom is ip -hybridized. The C atom forms sigma bonds with three O atoms. Thus the unhybridized 2p orbital of the C atom can simultaneously overlap the 2p orbitals of all three O atoms (Figure 10.29). The result is a delocalized molecular orbital that extends over all four nuclei in such a way that the electron densities (and hence the bond orders) in the carbon-to-... 

A rare example of T-shaped geometry is [Rh(PR3)3]+ (where R = C6H5), which (unlike its trigonal planar Pt analogue) has one P—Rh—P angle close to 180°, and the others near 90°, with Rh—P distances also not identical. Overall, trigonal planar is the dominant shape of three-coordination, and this is the shape predicted by Kepert s amended VSEPR model. 

Use valence shell electron pair repulsion (VSEPR) to predict geometry about any carbon or nitrogen atom. Count the number of other atoms attached to it and add to that the number of lone pair(s) it may contain. Two = linear and sp hybridized 3 = trigonal planar and sp2 hybridized 4 = tetrahedral and sp3. Not complicated. 

The isomers described to this point have had octahedral or square-planar geometry. In this section, we describe other geometries. Explanations for some of the shapes are consistent with VSEPR predictions (Chapter 3), with the general assumption that the metal d electrons are stereochemically inactive. In these cases, 3-coordinate complexes have a trigonal-planar shape, 4-coordinate complexes are tetrahedral, and so forth, assuming that... 

As we examine the common types of hybridization, notice the connection between the type of hybridization and certain of the molecular geometries predicted by the VSEPR model linear, bent, trigonal planar, and tetrahedral. 

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