Types of Hybrid Orbitals

To explain such facts, Linus Pauling proposed that the valence atomic orbitals in the molecule are different from those in the isolated atoms. Indeed, quantum-mechanical calculations show that if we mix specific combinations of orbitals mathematically, we obtain new atomic orbitals. The spatial orientations of these new orbitals lead to more stable bonds and are consistent with observed molecular shapes. The process of orbital mixing is called hybridization, and the new atomic orbitals are called hybrid orbitals. Two key points about the number and type of hybrid orbitals are that 

You can imagine hybridization as a process in which atomic orbitals mix, hybrid orbitals form, and electrons enter them with spins parallel (Hund s rule) to create stable bonds. In truth, though, hybridization is a mathematically derived result from quantum mechanics that accounts for the molecular shapes we observe. 

We postulate the presence of a certain type of hybrid orbital after we observe the molecular shape. As we discuss the five common types of hybridization, notice that the spatial orientation of each type of hybrid orbital corresponds with one of the five common electron-group arrangements predicted by VSEPR theory. 

To account for other molecular shapes within a given electron-group arrangement, we postulate that one or more of the hybrid orbitals contains lone pairs. In ozone (O3), for example, the central O is sp hybridized and a lone pair fills one of its three sp orbitals, so ozone has a bent molecular shape. 

Hybrid orbitals formed two sp three sp four sp five sp d 3 j2 SIX sp a 

SAMPLE PROBLEM 11.1 Postulating Hybrid Orbitals in a Molecule 

---

Now that we know how to determine hybridization states, we need to know the geometry of each of the three hybridization states. One simple theory explains it all. This theory is called the valence shell electron pair repulsion theory (VSEPR). Stated simply, all orbitals containing electrons in the outermost shell (the valence shell) want to get as far apart from each other as possible. This one simple idea is all you need to predict the geometry around an atom. First, let s apply the theory to the three types of hybridized orbitals. 

We generate hybrid orbitals on inner atoms whose bond angles are not readily reproduced using direct orbital overlap with standard atomic orbitals. Consequently, each of the electron group geometries described in Chapter 9 is associated with its own specific set of hybrid orbitals. Each type of hybrid orbital scheme shares the characteristics described in our discussion of methane ... 

The steric number of an inner atom uniquely determines the number and type of hybrid orbitals. 

The diagram shows the electron configuration of a normal carbon atom and the rearrangement of electrons to form four new identical orbits in a hybridized carbon atom. This type of hybrid orbital... 

When the number of electrons in the d orbitals is four, as in the case of Mn3+, there exists more than one possible type of hybrid orbital. For example, if the electrons remain unpaired in the d orbitals, there is only one orbital in the set that is empty. As a result, if an octahedral complex is formed, making... 

In view of the number and types of hybrid orbitals that are exhibited by ions of the transition metals when complexes are formed, it is possible to arrive at a summary of the most important types of complexes that each metal ion should form. Although there are many exceptions, the summary presented in Table 16.5 is a useful starting point for considering the types of complexes that are formed by metals in the first transition series. 

Hybridization occurs between two or more different types of orbitals (generally s, p or d orbitals). For example, there are three types of hybrid orbitals which may occur between the s and p orbitals, these are named as sp, sp2 and sp3 hybrid orbitals. 

The VSEPR theory is only one way in which the molecular geometry of molecules may be determined. Another way involves the valence bond theory. The valence bond theory describes covalent bonding as the mixing of atomic orbitals to form a new kind of orbital, a hybrid orbital. Hybrid orbitals are atomic orbitals formed as a result of mixing the atomic orbitals of the atoms involved in the covalent bond. The number of hybrid orbitals formed is the same as the number of atomic orbitals mixed, and the type of hybrid orbital formed depends on the types of atomic orbital mixed. Figure 11.7 shows the hybrid orbitals resulting from the mixing of s, p, and d orbitals. 

There are a number of different types of hybrid orbital, such as sp, sp2, and sp3. 

Predict the types of hybrid orbitals used in bonding by the central atom, the shape, and the bond angles in (a) In(CH3)3 (b) PC13 (c) IC12 (d) SiF62 . 

In addition to the two types of hybrid orbitals (sp and sp2) discussed so far, there are a number of others, representing different mixtures of atomic orbitals, that are commonly used in the description of directed covalent bonding. For example, one s and three p orbitals will lead to a set of four sp3 hybrid orbitals two dorbitals, one s orbital, and three p orbitals give a set of six d2spz orbitals. The general rule here is as follows ... 

There are several types of hybrid orbitals sp sp2 sp dsp- d spl etc. In order to figure out the type of hybrid orbital formed by an atom on the MCAT, simply count the number of sigma bonds and lone pairs of electrons on that atom. Match this number to the sum of the superscripts in a hybrid name (letters without superscripts are as- H sumed to have the superscript l ). Remember,... 

We conclude this section by discussing systems where there are two types of hybrid orbitals. One such example is NIH, where there are three equivalent bond hybrids and one lone pair hybrid. Another example is the water molecule. As shown in Fig. 3.4.11, hybrids hi and/12 are lone pairs orbitals, while hybrids... 

Magnetic moments provide the most direct way to determine the number of unpaired electrons in a metal ion. When the number of unpaired electrons is known, it is possible to use that information to deduce the type of hybrid orbitals that are used by the metal ion in bonding. 

The d orbitals have orientations as shown in Figure 19.2, and atomic orbitals must have the appropriate orientations (symmetry) for hybrid orbitals to form. For example, no hybrid orbitals are formed between the px and dyz orbital (those orbitals are orthogonal). A few of the common types of hybrid orbitals involved in bonding in complexes are shown in Table 19.4. 

The formation of single, double, and triple bonds in a molecule depends upon the types of hybridized orbitals that are sharing electrons. For example, when two hydrogen atoms bond to form H2(g), there is an overlap of s orbitals as shown in Figure 5.13. 

Figure 5.7 The orbital shapes of different types of hybridized orbitals...

To understand why this is so, we must look at the atomic orbitals used to form each type of hybrid orbital. A single 2s orbital is always used, but the number of 2p orbitals varies with the type of hybridization. A quantity called percent s-character indicates the fraction of a hybrid orbital due to the 2s orbital used to form it. 

Determine the types of hybrid orbitals that are consistent with the symmetry of the central atom in... 

FIGURE 6.44 Exact and approximate representations of the hybrid orbital shapes. For each type of hybrid orbital shown the left column shows typical chemists sketches, the center column shows isosurfaces, and the right column shows contour plots. The top row are the sp hybrid orbitals, the middle row are the sp hybrid orbitals, and the bottom row are the sp hybrid orbitals. 

Given the basic shapes of mononuclear molecules, cations and anions as determined by VSEPR theory, the bonding involved can then be described by the various types of hybrid orbitals, including double and triple bonding. In polynuclear molecules, VSEPR theory can be used to determine the stereochemistry at the separate atom centres present. Consequently the bonding at these separate atom centres can still be described by the appropriate types of hybrid orbitals, including multiple bonding. 

Note p orbitals are shaded in the diagrams. These models are meant to illustrate the locations and angles of hybrid and p orbitals relative to the central atom. A mathematical solution would also show that each type of hybrid orbital (sp3, sp2, and sp) has a slightly different shape from the other two. See Skill 1.2a for an image of electron density in a p orbital. 

The number of electron groups surrounding the central atom determines which types of hybridization orbital that surround the central atom and thus the orbital geometry around the central atom. 

Central Themes of VB Theory Types of Hybrid Orbitals... 

The type of hybrid orbitals obtained varies with the types of atomic orbitals mixed. 

Table 11.1 summarizes the numbers and types of atomic orbitals that are mixed to obtain the fi ve types of hybrid orbitals. Once again, note the similarities between the orientations of the hybrid orbitals proposed by VB theory and the shapes predicted by VSEPR theory (see Figure 10.3). Figure 11.8 (on the next page) shows the three conceptual steps from molecular formula to postulating the hybrid orbitals in the molecule, and Sample Problem 11.1 details the end of that process. 

Plan From the Lewis structure, we determine the number and arrangement of electron groups around each central atom, along with the molecular shape. From that, we postulate the type of hybrid orbitals involved. Then, we write the partial orbital diagram for each central atom before and after the orbitals are hybridized. 

VB theory explains that a covalent bond forms when two atomic orbitals overlap and two electrons with paired (opposite) spins occupy the overlapped region. Orbital hybridization allows us to explain how atomic orbitals mix and change their characteristics during bonding. Based on the observed molecular shape (and the related electron-group arrangement), we postulate the type of hybrid orbital needed. 

---