Predicting the Bond Angles

Predicting the bond angles is not as straightforward as predicting bond lengths, since they are more sensitive to steric effects which can only be taken into account once the bond network has been mapped into three-dimensional space. 

If the bonds are all equivalent in the bond graph, they are expected to be tmiformly distributed around the atom. The principle of maximum symmetry (1) predicts that three equivalent bonds will be arranged with threefold (triangular) symmetry as in BF3 and, four equivalent bonds will have tetrahedral 

Nonuniform environments occur if the ligands are different or have different environments in the bond graph so that the bonds are no longer equivalent. The symmetry may also be lost if electronic anisotropies such as stereoactive lone pairs are present (Sect. 7.1). In this section, we assume that lone pairs, if present, are not stereoactive. 

Any part of the flux linking the core of an atom to its valence shell belongs to one of the bonds formed by the atom (see Fig. 4), and because the atom is spherically symmetric, the solid angle, Q, subtended by this flux is a proportionate part of the total solid angle of 4 r steradians surrounding the core, leading to Eq. (15). 

An approach based on this idea has been shown to work well for calculating bond angles in tetrahedral coordination, as for example around the sulfur atom in sulfates [20], and as shown in Sect. 7 it is a useful approach to exploring the extent to which lone pairs are stereoactive. 

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Pyridoxal phosphate, a close relative of vitamin B6, is involved in a large number of metabolic reactions. TeJl the hybridization, and predict the bond angles for each nonterminal atom. 

Predict the bond angles at the central atom of the following molecules and ions (a) ozone, 03 (b) azide ion, N3 ... 

The Lewis structure of caffeine, C8H 0N4O2, a common stimulant, is shown below, (a) Give the hybridization of each atom other than hydrogen and predict the bond angles about that atom, (b) On the basis of your answers in part (a), estimate the bond angles around each carbon and nitrogen atom. 

C09-0031. Predict the bond angles for BCI3, SF4, and S11CI4. Which of these molecules, if any, has a dipole moment ... 

How can the VSEPR model help to predict the bond angles for these substances ... 

Predict the hybridization of the nitrogen atom in ammonia, NH3. Draw a picture of the three-dimensional structure of ammonia, and predict the bond angles. 

As the following examples show, in most cases the presence of lone pairs on the central atom makes it difficult to predict the bond angles accurately. 

Problem Draw the molecular shapes and predict the bond angles (relative to the ideal angles) of (a) PF3 and (b) COCI2. 

Step 3. Predict the bond angle For the tetrahedral electron-group arrangement, the ideal bond angle is 109.5°. There is one lone pair, so the actual bond angle should be less than 109.5°. 

Step 3. Predict the bond angles The ideal bond angle is 120°, but the double bond between C and O should compress the Cl—C—Cl angle to less than 120°. 

Consider the following compounds CO2, SO2, KrF2, SO3, NF3, IF3, CF4, SF4, XeF4, PF5, IF5, and SCIe. These 12 compounds are all examples of different molecular structures. Draw the Eewis structures for each and predict the molecular structure. Predict the bond angles and the polarity of each. (A polar molecule has a net dipole moment, while a nonpolar molecule does not.) See Exercises 105 and 106 for the molecular structures based on the trigonal bipyramid and the octahedral geometries. 

To predict the bond angles for the molecules, you would have to draw the Lew is structure and determine the geometry using the VSEPR model. From the geometry, you can predict tlie bond angles. 

Predict the bond angles around each atom designated with an arrow in glycine (an amino acid). 

Predict the bond angle in H30 . Name the shape of the molecule. 

JO In which of the following molecules can you confidently predict the bond angles about the central atom, and for which would you be a bit uncertain Explain in each case, (a) H2S, (b) BQ3, (c) CH3I, (d) CBr4, (e) TeBr4. 

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