Methane VSEPR model

The tetrahedral geometry of methane is often explained with the valence shell electron pair repulsion (VSEPR) model The VSEPR model rests on the idea that an electron pair either a bonded pair or an unshared pair associated with a particular atom will be as far away from the atom s other electron pairs as possible Thus a tetrahedral geomehy permits the four bonds of methane to be maximally separated and is charac terized by H—C—H angles of 109 5° a value referred to as the tetrahedral angle... 

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),... 

Organic molecules have specific three-dimensional shapes, which can be predicted by the VSEPR model (Section 7.9). When carbon is bonded to four atoms, as in methane, the bonds are oriented toward the four corners of a tetrahedron with carbon in the center and with H-C-H angles near 109.5° ... 

To see how the VSEPR model works, examine the methane (CH4) molecule. The first step is to write its Lewis structure. 

One of the most familiar compounds of carbon is methane, CH, the main component of natural gas. The methane molecule consists of a carbon atom with four hydrogen atoms bound to it in a tetrahedral fashion. That is, as predicted by the VSEPR model (see Chapter 12), the four pairs of bonding electrons around the carbon have minimum repulsions when they are located at the corners of a tetrahedron. 

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 ... 

According to the VSEPR model, the molecular geometry about each carbon atom in an alkane is tetrahedral. -= (Section 9.2) The bonding may be described as involving sp -hybridized orbitals on the carbon, as pictured in FIGURE 24.3 for methane. (Section 9.5)... 

The VSEPR model, simple as it is, does a surprisingly good job at predicting molecular shape, despite the fact that it has no obvious relationship to the filling and shapes of atomic orbitals. For example, we would like to understand how to account for the tetrahedral arrangement of C—H bonds in methane in terms of the 2s and 2p orbitals of the central carbon atom, which are not directed toward the apices of a tetrahedron. How can we reconcile the notion that covalent bonds are formed from overlap of atomic orbitals with the molecular geometries that come from the VSEPR model ... 

Methane is the simplest hydrocarbon. Physical and chemical studies show that all four C—H bonds are identical in length and strength and the molecule has a tetrahedral geometry with bond angles of 109.5°—consistent with the VSEPR model. How can we explain the tetravalency of carbon within the VB approach In its ground state, the electron configuration of carbon is [He]2/2p. Because the carbon... 

The three molecules of interest are methane (4A), ammonia (6A), and water (7A), shown first in the Lewis electron dot representations. Using the VSEPR model, these three molecules are drawn again using the wedge-dashed line notation. Methane (CH4, 4B) has no unshared electrons on carbon but there are electrons in the C-H covalent bonds. Assume that repulsion of the electrons in the bonds leads to a tetrahedral arrangement to minimize electronic repulsion. Ammonia (H3N, 6B) has a tetrahedral array around nitrogen if the electron pair is taken into account. If only the atoms are viewed, however, 6B has the pyramidal shape shown. Water (HOH, 7B) has two electron pairs that occupy the corners of a tetrahedral shape, as shown. 

Methane, CH4, has steric number 4, and VSEPR predicts a tetrahedral structure, which is confirmed by experimental results. Starting with the electron configuration C (ls) (2s) (2p), the VB model cannot account for the formation of CH4 and predicts that CH2 would be the stable hydride, which is again contrary to the... 

We can use the example of the balloons to model the shapes that methane (CH4), ammonia (NH3), and water (HgO) assume. As you look at each of these molecules in Figures 1.6-1.8, take note of (1) the number of regions of electron density shown by the Lewis structure, (2) the geometry that is required to maximize the separation of these regions of electron density, and (3) the names of the shapes that result from this treatment using VSEPR. 

Examine the ball-and-stick models for water and methane as drawn in Figure 6.23. In terms of the VSEPR theory, how are these models the same and how are they different ... 

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