Localized electron model hybrid orbitals

Describe the bonding in SO2 and SO3 using the localized electron model (hybrid orbital theory). How would the molecular orbital model describe the tt bonding in these two compounds ... 

Follow the four-step procedure for the composite model of bonding. Use localized bonds and hybrid orbitals to describe the bonding framework and the inner atom lone pairs. Next, analyze the system, paying particular attention to resonance structures or conjugated double bonds. Finally, make sure the bonding inventory accounts for all the valence electrons and all the valence orbitals. 

Carbon occurs in the allotropes (different forms) diamond, graphite, and the fullerenes. The fullerenes are molecular solids (see Section 16.6), but diamond and graphite are typically network solids. In diamond, the hardest naturally occurring substance, each carbon atom is surrounded by a tetrahedral arrangement of other carbon atoms, as shown in Fig. 16.26(a). This structure is stabilized by covalent bonds, which, in terms of the localized electron model, are formed by the overlap of sp3 hybridized atomic orbitals on each carbon atom. 

By this point in your study of chemistry, you no doubt recognize that the localized electron model, although very simple, is a very useful model for describing the bonding in molecules. Recall that a central feature of the model is the formation of hybrid atomic orbitals that are used for sharing electron pairs to form cr bonds between atoms. This same model can be used to account for the bonding in complex ions, but there are two important points to keep in mind. 

The simplest member of the saturated hydrocarbons, which are also called the alkanes, is methane (CH4). As discussed in Section 14.1, methane has a tetrahedral structure and can be described in terms of a carbon atom using an sp-J hybrid set of orbitals to bond to the four hydrogen atoms (see Fig. 22.1). The next alkane, the one containing two carbon atoms, is ethane (C2H6), as shown in Fig. 22.2. Each carbon in ethane is surrounded by four atoms and thus adopts a tetrahedral arrangement and sp3 hybridization, as predicted by the localized electron model. 

A special class of cyclic unsaturated hydrocarbons is known as the aromatic hydrocarbons. The simplest of these is benzene (C6H6), which has a planar ring structure, as shown in Fig. 22.11(a). In the localized electron model of the bonding in benzene, resonance structures of the type shown in Fig. 22.11(b) are used to account for the known equivalence of all the carbon-carbon bonds. But as we discussed in Section 14.5, the best description of the benzene molecule assumes that sp2 hybrid orbitals on each carbon are used to form the C—C and C—H a bonds, while the remaining 2p orbital on each carbon is used to form 77 molecular orbitals. The delocalization of these 1r electrons is usually indicated by a circle inside the ring [Fig. 22.11(c)]. 

Very similar treatments can be applied to other planar molecules for which resonance is required by the localized electron model. For example, the NO3 ion can be described using the tt molecular orbital system shown In Fig. 9.48. In this molecule each atom is assumed to be sp hybridized, which leaves one p orbital on each atom perpendicular to the plane of the Ion. These p orbitals can combine to form the tt molecular orbital system. 

Localized electron model The central oxygen atom is sp hybridized, which is used to form the two cr bonds and hold the lone pair of electrons. An unchanged (unhybridized) p atomic orbital forms the tt bond with the neighboring oxygen atoms. The actual structure of O3 is an average of the two resonance structures. Molecular orbital model There are two localized cr bonds and a tt bond that is delocalized over the entire surface of the molecule. The delocalized TT bond results from overlap of a p atomic oribtal on each oxygen atom in O3. 59. 

The Localized Electron Model and Hybrid Orbitals 17. Use (he localized electron model to describe die bonding ii... 

Hybridization is a modification of the localized electron model to account for the observation that atoms often seem to use special atomic orbitals in forming molecules. 

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