Electron-Group Arrangements and Molecular Shapes

It s important to realize that we use the VSEPR model to account for the molecular shapes observed by means of various laboratory instruments. In almost 

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Follow the four-step procedure that helps to predict molecular shape. Use Table 4.2 for names of the electron-group arrangements and molecular shapes. 

Valence-Shell Electron-Pair Repulsion (VSEPR) Theory and Molecular Shape Electron-Group Arrangements and Molecular Shapes... 

In the following ExpressLab, you will make models of the five electron-group arrangements, and measure their bond angles. Afterwards, you will consider some of the variations in molecular shapes that can occur... 

However, this Lewis structure seems to indicate that the five atoms are all located in the same plane and that the angles between the atoms are all 90° or 180°. This is not true. The aaual shape of a molecule can be more accurately predicted by recognizing that the negatively charged electrons that form covalent bonds and lone pairs repel each other. Therefore, the most stable arrangement of the electron-groups is the molecular shape that keeps the groups as far away from each other as possible. 

Describe the five electron-group arrangements and associated molecular shapes, predict molecular shapes from Lewis structures, and explain deviations from ideal bond angles ( 10.2) (SPs 10.6-10.8) (EPs 10.25-10.49)... 

Table 4.2 Common Molecular Shapes and Their Electron Group Arrangements... 

Figure 10.3 Electron-group repulsions and the five basic molecular shapes. A, As an analogy for electron-group arrangements, two to six attached balloons form five geometric orientations such that each balloon occupies as much space as possible. B, Mutually repelling...

Figure 10.4 The single molecular shape of the linear electron-group arrangement. The key (bottom) for A, X, and E also refers to Figures 10.5, 10.6, 10.8, and 10.9.

Determine the electron-group arrangement, molecular shape, and ideal bond angle(s) for each of the following ... 

To account for other molecular shapes within a given electron-group arrangement, we postulate that one or more of the hybrid orbitals contains lone pairs. In ozone (O3), for example, the central O is sp hybridized and a lone pair fills one of its three sp orbitals, so ozone has a bent molecular shape. 

Figure 11.5 shows the bonding in other molecular shapes with the tetrahedral electron-group arrangement. The trigonal pyramidal shape of NH3 arises when a lone pair fills one of the four sp orbitals of N, and the bent shape of H2O arises when lone pairs fill two of the sp orbitals of O. 

VB theory explains that a covalent bond forms when two atomic orbitals overlap and two electrons with paired (opposite) spins occupy the overlapped region. Orbital hybridization allows us to explain how atomic orbitals mix and change their characteristics during bonding. Based on the observed molecular shape (and the related electron-group arrangement), we postulate the type of hybrid orbital needed. 

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