Space-filling models methane

FIGURE 1 6 Molecular models of methane (CH4) (a) Framework (tube) models show the bonds connecting the atoms but not the atoms themselves (b) Ball and stick (ball and spoke) models show the atoms as balls and the bonds as rods (c) Space filling models portray overall molecular size the radius of each sphere approximates the van der Waals radius of the atom (d) An electrostatic potential map of methane... 

As useful as molecular models are, they are limited in that they only show the location of the atoms and the space they occupy. Another important dimension to molecular structure is its electron distribution. We introduced electrostatic potential maps in Section 1.5 as a way of illustrating charge distribution and will continue to use them throughout the text. Figure 1.6(d) shows the electrostatic potential map of methane. Its overall shape is similar to the volume occupied by the space-filling model. The most electron-rich regions are closer to carbon and the most electron-poor ones are closer to the hydrogens. 

Representations of tetrahedral methane (a) space-filling model (b) ball-and-stick model (c) ball-and-stick model, highlighting the tetrahedral faces (d) ball-and-stick drawing using wedge representations for the out-of-plane bonds. 

Note that 1 have used several models for methane, beginning with CH4. This representation of methane is clearly incomplete but it does communicate one essential feature of the molecule its composition. 1 have also introduced a ball-and-stick model for methane. There is another useful model for methane that 1 have not intfoduced— a space-filling model. Here it is ... 

Ball-and-stick model of methane Space-filling model of methane... 

Space-filling model of the methane molecule. This type of model shows both the relative sizes of the atoms in the molecule and their spatial relationships. 

In a compound composed of molecules, the individual molecules move around as independent units. For example, a methane molecule is represented in Fig. 2.15 using a space-filling model. These models show the relative sizes of the atoms, as well as their relative orientation in the molecule. Figure 2.16 shows other examples. Ball-and-stick models are also used to represent molecules. The ball-and-stick model of methane is shown in Fig. 2.17. 

FIGURE 10.10 (a) Space-filling models, (b) 0.002 e/(ao) electron density isosurfaces, and (c) electrostatic potential energy surfaces for water, ammonia, and methane. 

Figures 10.10a and b show, respectively, space-filling models and electron density isosurfaces plotted at 0.002 e/(tZo) for water, ammonia, and methane. The electron densities plotted here include all of the electrons in the molecule. They are calculated using state-of-the-art ab initio quantum chemical methods (see discussion in Chapter 6).

Figure 21-2 Representations of a molecule of methane, CH4. (a) The condensed and Lewis formulas for methane, (b) The overlap of the four sp carbon orbitals with the s orbitals of four hydrogen atoms forms a tetrahedral molecule, (c) A ball-and-stick model, (d) a space-filling model of methane, and (e) a three-dimensional representation that uses the wedged line to indicate a bond coming forward and a dashed line to represent a bond projecting backward.

The space-filling model of methane displays the symmetry of the molecule. 

Compare and contrast the information given in the Lewis structure, the space-filling model, the hall-and-stick model, and the geometric sketch of a methane molecule, CH4. 

FIGURE 12.5 The structure of methane, as represented by (a) its structural formula, (b) a ball-and-stiek model, (e) a space-filling model, and (d) a wedge-dash projection showing the geometry of the molecule. 

A Figure 2.17 Different representations of the methane (CH4) moiecuie. Structural formulas, perspective drawings, ball-and-stick models, and space-filling models. 

Note that the four hydrogen atoms are distributed to the corners of an imaginary tetrahedron in three-dimensional space around the carbon of 4d, which is buried in the center of the tetrahedron. In addition, a three-dimensional molecular model of methane is shown where cylinders represent the bonds and spheres represent the atoms (4e), which is the so-called ball-and-stick model. The bonds represented by wedges and dashed lines in the two-dimensional model are marked in 4e. A so-called space-filling model, 4f, is also shown to illustrate the relative size of the atoms. Both types of molecular models (ball and stick or space filling) will be used for other molecules in various places in the book. 

Figure 3-1 Three representations of the reaction of methane with oxygen to form carbon dioxide and water. Chemicai bonds are broken and new ones are formed in each representation. Part (a) iiiustratesthe reaction using baii-and-stick modeis, (b) uses chemical formulas, and (c) uses space-filling models.

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