Lewis structures applying VSEPR theory

Deriving Lewis Structures and Applying VSEPR Theory... 

Structure of a molecule with more than one central atom, we look at each atom within the backbone of the molecule and predict the bonding about that atom, using the same procedures that we have just outlined. For example, let s see what happens when we apply VSEPR theory to the structure of tetrafluoroethylene (C2F4, the monomer from which PTFE is produced). The Lewis structure we drew in Example Problem 7.6 is a good place to start. 

Strategy Draw Lewis dot structures and apply VSEPR theory [ HI Section 9.2] to determine whether each molecule is polar or nonpolar. Nonpolar molecules exhibit dispersion forces only. Polar... 

First, determine the empirical formula of nitryl fluoride from the composition data and the molar mass based on that formula. Next, determine the true molar mass from the vapor density data. Now the two results can be compared to establish the molecular formula. Then, write a plausible Lewis structure based on the molecular formula, and apply VSEPR theory to the Lewis structure to predict the molecular shape. Finally, assess the polarity of the molecule from the molecular shape and electronegativity values. 

We can use data from Table 10.2 to estimate the bond order for the two nitrogen-to-nitrogen bonds. From this information we can write plausible Lewis structures, and by applying VSEPR theory to the Lewis structures, we can predict a likely geometric shape of the molecule. Finally, with this information we can propose hybridization schemes for the central atoms and an overall bonding scheme for the molecule. 

If we can draw Lewis structures for covalent molecules, we can predict their shapes by applying a few simple rules. The theory that accounts for the shapes of molecules is called valence shell electron pair repulsion theory (VSEPR theory) and is based on the reasoning that electron pairs attempt to get as far away from other electron pairs as possible because their negative charges repel each other. 

Draw Lewis structures for the following molecules, apply the VSEPR theory, and predict the shape of each molecule ... 

Predict the shape of each of the following molecules by first drawing a Lewis structure, then applying the VSEPR theory ... 

Although molecular orbital theory is in many ways the most powerful of the bonding models, it is also the most complex, so we continue to use the other models when they do an adequate job of explaining or predicting the properties of a molecule. For example, if you need to predict the three-dimensional shape of an AB molecule on an exam, you should draw its Lewis structure and apply the VSEPR model. Don t try to draw its molecular orbital diagram. On the other hand, if you need to determine the bond order of a diatomic molecule or ion, you should draw a molecular orbital diagram. In general chemistry, it is best to use the simplest theory that can answer a particular question. 

Strategy Consider the structure of each solute to determine whether or not it is polar. For molecular solutes, start with a Lewis structure and apply the VSEPR theory [M< Section 9.1]. We expect polar solutes, including ionic compounds, to be more soluble in water. Nonpolar solutes will be more soluble in benzene. 

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