Lewis structures VSEPR theory

These questions and other aspects concerning energy considerations, molecular orbital theory, Lewis structures, VSEPR theory and orbital hybridization theory will be answered and covered in this section. 

Tutorials Animated examples and interactive activities Lewis Structures VSEPR Theory... 

The Lewis structures encountered in Chapter 2 are two-dimensional representations of the links between atoms—their connectivity—and except in the simplest cases do not depict the arrangement of atoms in space. The valence-shell electron-pair repulsion model (VSEPR model) extends Lewis s theory of bonding to account for molecular shapes by adding rules that account for bond angles. The model starts from the idea that because electrons repel one another, the shapes of simple molecules correspond to arrangements in which pairs of bonding electrons lie as far apart as possible. Specifically ... 

Draw Lewis structures for the following molecules and ions, and use VSEPR theory to predict the molecular shape. Indicate the examples in which the central atom has an expanded octet. 

CD If possible for your material, draw a Lewis structure of the molecule or molecules on which your material is based. Predict the molecular shape using VSEPR theory. 

Use Lewis structures and VSEPR theory to predict the geometry of the following molecules. 

The interhalogen compounds obey the expectations based on the VSEPR theory, and typical structures are giver in Chapter 6. Ore compound not included there is the dimeric iodine trichloride, in which the iodine atom of the monomeric species appears to act as a Lewis acid and accept an additional pair of electrons from a chlorine atom (Fig. 17.5). 

Using Lewis structures and VSEPR theory, predict the shape of each of the following species (a) sulfur tetrachloride (b) iodine trichloride (c) IF4 (d) xenon trioxide. Give the VSEPR AX Em designation for each. 

Using Lewis structures and VSEPR theory, predict the shape of each of the following species (a) PF4 ... 

Solid phosphorus pentachloride exists as PC14+PC16. Write the Lewis structures for the two ions and predict their shapes from VSEPR theory. 

Xenon hexafluoride exists as the ionic solid XeFs+F. Write the Lewis structure for XeF5+ and, from VSEPR theory, predict its shape. 

An advantage of VSEPR is its foundation upon Lewis electron-pair bond theory. No mention need be made of orbitals and overlap. If you can write down a Lewis structure for the molecule or polyatomic ion in question, with all valence electrons accounted for in bonding or nonbonding pairs, there should be no difficulty in arriving at the VSEPR prediction of its likely shape. Even when there may be some ambiguity as to the most appropriate Lewis structure, the VSEPR approach leads to the same result. For example, the molecule HIO, could be rendered, in terms of Lewis theory as ... 

Now, what about carbon dioxide Well, when we draw a Lewis structure of carbon dioxide, and consider VSEPR theory, we arrive at a linear molecule, as illustrated in Figure 7.15. Each C-O bond is polarized towards the oxygen. However, the two bond dipoles are pointing in exactly opposite directions, and cancel each other out. Therefore, carbon dioxide is a nonpolar molecule. 

Valence Bond Theory 157 Bond Length and Bond Energy 158 Lewis Structures 159 VSEPR Theory 161... 

In all the three molecules, the central atom has four shared pairs of electrons like AB4 discussed in (c) above. The favourable geometrical arrangement according to VSEPR theory, which keeps the shared pairs of electrons as far as possible, should be tetrahedral like CH4, CC14, etc. But the actual geometry is different which can be easily followed when we look at their Lewis structures given above. 

The shapes of molecules are determined by actual experiments, not by theoretical considerations. But we do not want to have to memorize the shape of each molecule. Instead, we would like to be able to look at a Lewis structure and predict the shape of the molecule. Several models enable us to do this. One of the easiest to use is valence shell electron pair repulsion theory, which is often referred to by its acronym VSEPR (pronounced vesper ). As the name implies, the theory states that pairs of electrons in the valence shell repel each other and try to stay as far apart as possible. You probably remember this theory from your general chemistry class. The parts of VSEPR theory that... 

Obviously, the formulas CO2 and SO2 do not provide any information about the shapes of these molecules. However, there is a model that can be used to predict the shape of a molecule. This model is based on the valence shell electron pair repulsion (VSEPR) theory. Using this model, you can predict the shape of a molecule by examining the Lewis structure of the molecule. 

According to the VSEPR theory, the shape of a molecule is determined by the valence electrons surrounding the central atom. For example, examine the Lewis structure for CO2. 

Predict the structure of hydrazine (H2NNH2) by writing down its Lewis diagram and using the VSEPR theory. What is the hybridization of the two nitrogen atoms ... 

Discuss the nature of the bonding in the nitrite ion (NO2). Draw the possible Lewis resonance diagrams for this ion. Use the VSEPR theory to determine the steric numbeg the hybridization of the central nitrogen atom, and the geometry of the ion. Show how the use of resonance structures can be avoided by introducing a de-localized 77 MO. What bond order does the MO model predict for the N—O bonds in the nitrite ion ... 

This chapter provides a substantial introduction to molecular structure by coupling experimental observation with interpretation through simple classical models. Today, the tools of classical bonding theory—covalent bonds, ionic bonds, polar covalent bonds, electronegativity, Lewis electron dot diagrams, and VSEPR Theory—have all been explained by quantum mechanics. It is a matter of taste whether to present the classical theory first and then gain deeper insight from the... 

A provisional Lewis structure may contain the correct bonding framework, but the distribution of the valence electrons may not be the one that gives the maximum stability. The correct stereochemistry is predicted by the valence shell configuration using VSEPR theory, as shown in Chapter 6. A concept called formal charge (FC) can be used to predict which structure of a number of alternative structures is the most reasonable for a Lewis structure. The formal charge (FC) on any atom in a Lewis structure can be defined as ... 

---