Electron-domain geometry

TABLE 9.1 Electron-Domain Geometries as a Function of Number of Electron Domains... 

The arrangement of electron domains about the central atom of an AB molecule or ion is called its electron-domain geometry. In contrast, the molecular geometry is the arrangement of only the atoms in a molecule or ion—any nonbonding pairs in the molecule are ot part of the description of the molecular geometry. 

Determine the electron-domain geometry by arranging the electron domains about the central atom so that the repulsions among them are rninirnized, as shown in Table 9.1. 

Because the trigonal-pyramidal molecular geometry is based on a tetrahedral electron-domain geometry, the ideal bond angles are 109.5°. As we will soon see, bond angles deviate from ideal values when the surrounding atoms and electron domains are not identical. 

Determine electron-domain geometry by coimting all electron domains, then use Table 9.1 to determine appropriate electron domain geomtiy. 

Two electron domains orient in a linear electron-domain geometry (Table 9.1). Because neither domain is a nonbonding pair of electrons, the molecular geometry is also linear, and the O—C— O bond angle is 180°. 

Plan To predict the molecular geometries, we draw their Lewis structures and count electron domains around the central atom to get the electron-domain geometry. We then obtain the molecular geometry fiom the arrangement of the domains that are due to bond ... 

We can refine the VSEPR model to explain slight distortions from the ideal geometries summarized in Table 9.2. For example, consider methane (CH4), ammonia (NH3), and water (H2O). All three have a tetrahedral electron-domain geometry, but their bond angles differ slightly ... 

Section 8.7) Molecules with five or six electron domains around the central atom have molecular geometries based on either a trigonal-bipyramidal (five domains) or octahedral (six domains) electron-domain geometry ( TABLE 9.3). 

Plan We first draw Lewis structures and then use the VSEPR model to determine the electron-domain geometry and molecular geometry. 

The iodine has six electron domains around it, one of which is nonbonding. The electron-domain geometry is therefore octahedral, with one position occupied by the nonbonding pair, and the molecular geometry is square pyramidal (Table 9.3) ... 

Although the electron-domain geometry around the right 0 is tetrahedral, the C—0—H bond is slightly less than 109.5°. Explain. 

Electron-domain geometry tetrahedral, molecular geometry tetrahedral... 

Electron-domain geometry trigonal planar, molecular geometry trigonal planar... 

Electron-domain geometry Tetrahedral Trigonal planar Tetrahedral... 

Overall, hybrid orbitals provide a convenient model for using valence-bond theory to describe covalent bonds in molecules in which the molecular geometry conforms to the electron-domain geometry predicted by the VSEPR modeb The picture of hybrid orbitals has limited predictive value. When we know the electron-domain geometry, however, we can employ hybridization to describe the atomic orbitals used by the central atom in bonding. 

Determine electron-domain geometry about central atom from VSEPR model and Table 9.1... 

Plan To determine the central atom hybrid orbitals, we must know the electron-domain geometry around the atom. Thus, we draw the Lewis structure to determine the number of electron domains around the central atom. The hybridization conforms to the number and geometry of electron domains around the central atom as predicted by the VSEPR model... 

Because there are four electron domains around N, the electron-domain geometry is tetrahedral The hybridization that gives a tetrahedral electron-domain geometry is sp (Table 9.4). Two of the sp hybrid orbitals contain nonbonding pairs of electrons, and the other two are used to make bonds with the hydrogen atoms. 

Predict the electron-domain geometry and hybridization of the central atom in 803 Answer tetrahedral, sp ... 

In each structure, the electron-domain geometry at nitrogen is trigonal planar, which implies sp hybridization of the N atom. The sp hybrid orbitals are used to constmct the three N — O (7 bonds present in each resonance stmcture. 

SECTION 9.5 To extend the ideas of valence-bond theory to polyatomic molecules, we must envision mixing s, p, and sometimes d orbitals to form hybrid orbitals. The process of hybridization leads to hybrid atomic orbitals that have a large lobe directed to overlap with orbitals on another atom to make a bond. Hybrid orbitals can also accommodate nonbonding pairs. A particular mode of hybridization can be associated with each of three common electron-domain geometries (linear = sp trigonal planar = sp -, tetrahedral = sp ). 

For each molecule (a)-(f), indicate how many different electron-domain geometries are consistent with the molecular geometry shown. [Section 9.2]... 

Describe the characteristic electron-domain geometry of each of the following numbers of electron domains about a central atom (a) 3, (b) 4, (c) 5, (d) 6. 

What is the difference between the electron-domain geometry and the molecular geometry of a molecule Use the water molecule as an example in your discussion. Why do we need to make this distinction ... 

An AB3 molecule is described as having a trigonal-bipyramidal electron-domain geometry. How many nonbonding domains... 

Consider the molecule PF4CI. (a) Draw a Lewis structure for the molecule, and predict its electron-domain geometry, (b)... 

Which would you expect to take up more space, a P—Fbond or a P—Cl bond Explain, (c) Predict the molecular geometry of PF4CL How did your answer for part (b) influence your answer here in part (c) (d) Would you expect the molecule to distort from its ideal electron-domain geometry If so, how would it distort ... 

The Lewis structure shows that each atom has two electron domains. (Each nitrogen has a nonbonding pair of electrons and a triple bond, whereas each carbon has a triple hond and a single bond.) Thus, the electron-domain geometry around each atom is linear, causing the overall molecule to be linear. 

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