Molecular shapes VSEPR

Electronegativity and bond type (Bl) Molecular shapes VSEPR (C2)... 

Guide to Predicting Molecular Shape (VSEPR Theoiy)... 

Calculations for Percent Yield 293 Calculations Using the Heat of Reaction (AW) 297 Drawing Electron-Dot Formulas 308 Predicting Molecular Shape (VSEPR Theory) 317... 

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 ... 

STRATEGY For the electron arrangement, draw the Fewis structure and then use the VSEPR model to decide how the bonding pairs and lone pairs are arranged around the central (nitrogen) atom (consult Fig. 3.2 if necessary). Identify the molecular shape from the layout of atoms, as in Fig. 3.1. 

Give the VSEPR formula, molecular shape, and bond angles for each of the following species (a) I, (b) SbCl5 ... 

Having introduced methane and the tetrahedron, we now begin a systematic coverage of the VSEPR model and molecular shapes. The valence shell electron pair repulsion model assumes that electron-electron repulsion determines the arrangement of valence electrons around each inner atom. This is accomplished by positioning electron pairs as far apart as possible. Figure 9-12 shows the optimal arrangements for two electron pairs (linear),... 

Tetrahedral geometry may be the most common shape in chemistry, but several other shapes also occur frequently. This section applies the VSEPR model to four additional electron group geometries and their associated molecular shapes. 

The carbon atom in CO2 has two groups of electrons. Recall from our definition of a group that a double bond counts as one group of four electrons. Although each double bond includes four electrons, all four are concentrated between the nuclei. Remember also that the VSEPR model applies to electron groups, not specifically to electron pairs (despite the name of the model). It is the number of ligands and lone pairs, not the number of shared eiectrons, that determines the steric number and hence the molecular shape of an inner atom. 

First we must draw the Lewis structure for all of the species listed. Following this, we will deduce their electron-group geometries and molecular shapes following the VSEPR... 

C3V o shape (Fig. 4.5(a)), ReH5 (Fig. 4.7(b)) resembles the idealized ML5 Cs shape (Fig. 4.4(a)), OsH4 (Fig. 4.7(c)) is the idealized ML4 Td shape (Fig. 4.3(a)), and so forth. Thus, the rather unusual hydride geometries immediately suggest the role of sdM hybridization and covalency, leading to molecular shapes quite unlike those expected from simple ionic or packing ( VSEPR-like 15) forces.16... 

You can use soap bubbles to simulate the molecular shapes that are predicted by VSEPR theory. The soap bubbles represent the electron clouds surrounding the central atom in a molecule. 

Table 4.2 summarizes the molecular shapes that commonly occur. The VSEPR notation used for these shapes adopts the letter A to represent the central atom, the letter X to represent a bonding pair, and the letter E to represent a lone pair of electrons. For example, the VSEPR notation for NH3 is AX3E. This indicates that ammonia has three BPs around its central atom, and one LP. 

Number of electron groups Geometric arrangement of electron groups Type of electron pairs VSEPR notation Name of Molecular shape Example... 

This molecular shape corresponds to the VSEPR notation for this ion, AXgE. 

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. 

Use VSEPR theory to predict the shape of each of the following molecules. From the molecular shape and the polarity of the bonds, determine whether or not the molecule is polar. 

Q iai f For the compound, GeH4, use VSEPR theory to determine its molecular shape and indicate whether or not this molecule is polar. 

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 VSEPR theory to predict the molecular shape of CH2CI2. Draw a sketch to indicate the polarity of the bonds around the central atom to verify that this is a polar molecule. 

The basis of the VSEPR theory is that the shape of a molecule (or the geometry around any particular atom connected to at least two other atoms) is assumed to be dependent upon the minimization of the repulsive forces operating between the pairs of sigma (a) valence electrons. This is an important restriction. Any pi (7t) or delta (8) pairs are discounted in arriving at a decision about the molecular shape. The terms sigma , pi and delta refer to the type of overlap undertaken by the contributory atomic orbitals in producing the molecular orbitals, and are referred to by their Greek-letter symbols in the remainder of the book. 

Two major theories of the covalent bond are described in this book the main features of valence bond theory are treated in terms of the VSEPR theory of molecular shapes, and MO theory which is based on the symmetry properties of the contributing atomic orbitals. The latter theory is applied qualitatively with MO diagrams being constructed and used to interpret bond orders and bond angles. The problems associated with bond angles are best treated by using the highest symmetry possible for a molecule of a particular stoichiometry. 

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