Methane tetrahedral shape

Methane is the simplest molecule with a tetrahedral shape, but many molecules contain atoms with tetrahedral geometry. Because tetrahedral geometry is so prevalent in chemistry, it is important to be able to visualize the shape of a tetrahedron. 

Figure 1.31 A tetrahedral shape for methane allows the maximum separation of the four bonding electron pairs.

Ammonia, (NH3) has a pyramidal shape. Methane, (CH4) has a tetrahedral shape. 

The carbon two-valent state is converted to its four-valent state by unpairing the 2s electrons and promoting one of them to the third 2p orbital. The electrons from the four hydrogen atoms (red) make up four pairs of or bonding electrons, which repel each other to a position of minimum repulsion to give the tetrahedral shape for the methane molecule. 

We still have not explained methane s tetrahedral shape and its four identical bonds. At this stage, it looks as though electron promotion should result in two different types of bonds, one from the overlap of a hydrogen ls-orbital and a carbon 2s-orbital, and three more bonds from the overlap of hydrogen ls-orbitals with each of the three carbon 2p-orbitals. The overlap with the 2p-orbitals should result in three n-bonds at 90° to one another. 

Because valence electron octets are so common, particularly for second-row elements, the atoms in a great many molecules have shapes based on the tetrahedron. Methane, for example, has a tetrahedral shape, with H-C-H bond angles of 109.5°. In NH3, the nitrogen atom has a tetrahedral arrangement of its four charge clouds, but one corner of the tetrahedron is occupied by a lone pair, resulting in a trigonal pyramidal shape for the molecule. Similarly, H20 has two corners of the tetrahedron occupied by lone pairs and thus has a bent shape. 

Make your own clay. Find an area in your community where the soil is tightly packed and resembles clay. Dig out a ball of this soil. Add just enough water to make the soil plastic. Sculpt your clay into a molecular shape. It might be a bent water molecule or a tetrahedral-shaped methane molecule. Let your molecular model dry in sunlight. Paint your molecular model sculpture. 

Considering the tetrahedral shape of methane, construct a multiple-methane-molecule sculpture, or draw a picture of such an arrangement. Explain why the sculpture or drawing is abstract or nonobjective. How do the shapes in the sculpture or drawing evoke a mood or emotion How do the shapes show direction or movement ... 

Drawing the Lewis structure of a molecule can help you determine the molecule s shape. In Figure 3.30, you can see the shape of the ammonia, NH3, molecule. The ammonia molecule has three bonding electron pairs and one lone pair on its central atom, all arranged in a nearly tetrahedral shape. Because there is one lone pair, the molecule s shape is pyramidal. The molecule methane, CH4, is shown in Figure 3.31. This molecule has four bonding pairs on its central atom and no lone pairs. 

Both the tetraarsene, AS4, and the methane, CH4, molecules have tetrahedral shapes (Figure 3-16) and Td symmetry. However, there is an important difference in their structures. In the As4 molecule, all... 

D Methane, because of its tetrahedral shape, is a nonpolar molecule. Nonpolar molecules will not exhibit dipole attractions. 

The isoelectronic molecules CH4, NH3, and H2O (Figure 3-10) illustrate the effect of lone pairs on molecular shape. Methane has four identical bonds between carbon and each of the hydrogens. When the four pairs of electrons are arranged as far from each other as possible, the result is the familiar tetrahedral shape. The tetrahedron, with all H—C — H angles measuring 109.5°, has four identical bonds. 

Because methane has a tetrahedral shape, with the H C-H bond angles 109° 28, the more accurate method of showing the shapes and bond angles of the alkanes is shown in Figure 6.4.1. 

B. H20]—Carbon dioxide and diatomic nitrogen have a linear shape. Methane has a tetrahedral shape. Water is the classic example of a bent shape. 

We consider the shape of the molecule to be determined by the arrangement of only the joined atoms. That is why, although the CH4, NH3 and H2O molecules each have four pairs of electrons around the central atom, methane has the tetrahedral shape, ammonia is trigonal pyramidal, and water is bent. 

The polyhedral description may be useful for widely different systems. Thus, for example, both the tetraarsene, As, and the methane, CH, molecules have tetrahedral shapes (Figure 3-23) and symmetry. However, there is an important difference in their structures. In the As molecule all the four constituent nuclei are located at the vertices of a regular tetrahedron, and all the edges of this tetrahedron are chemical bonds between the As atoms. In the methane molecule, there is a central carbon atom, and four chemical bonds are... 

The simplest hydrocarbon molecule, methane, has a tetrahedral shape, with the carbon atom at the center of the tetrahedron and the four hydrogen atoms at the corners. Every carbon atom in a saturated hydrocarbon molecule has its bonds tetrahedrally arranged. This arrangement allows the hydrogen atoms bonded to carbon atoms to be located as far as possible from one another. 

We have seen that the tetrahedral shape of methane is consistent with a bonding model based on sp hybrid orbitals on carbon. We should not conclude, however, that the geometry is a result of sp hybridization. We... 

The valence shell of methane contains four pairs of bonding electrons. Only a tetrahedral orientation will allow four pairs of electrons to have equal and maximum possible separation from each other (Fig. 1.33). Any other orientation, for example, a square planar arrangement, places some electron pairs closer together than others. Thus, methane has a tetrahedral shape. 

Actually, these compounds have a tetrahedral shape with bond angles of 109.5° (see Figure 19.2), but the bonds are often drawn at right angles. In methane each bond is formed by the sharing of electrons between a carbon and a hydrogen atom. 

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. 

The carbon and hydrogen that compose methane have only slightly different electronegativities, making the bonds between them mostly nonpolar. Any slight polarity present in each bond is canceled by the tetrahedral shape of the molecule, making methane a nonpolar molecule. Every other hydrocarbon is also nonpolar (like methane), resulting in the inability of hydrocarbons to mix with polar substances such as water. 

Representations of methane and ethane have been updated to emphasize the tetrahedral shape. 

For example, to explain the tetrahedral geometry of CH, we say that carbon s 2s and three 2p orbitals blend together, or hybridize, to form four sp hybrid orbitals. (Four atomic orbitals combine to make four hybrid orbitals.) The four sp orbitals, following VSEPR, orient themselves toward the vertices of a regular tetrahedron, hence methane s tetrahedral shape. 

Now let s consider methane. Methane is a nonpolar molecule. This is evident first because there are no nonbonding electron pairs, and secondly because there is relatively httle electronegativity difference between the hydrogens and the central carbon. Furthermore, what little electronegativity difference there is between the hydrogens and the central carbon atom is negated by the symmetrical distribution of the C-H bonds in the tetrahedral shape of methane. The slight polarity of each C H bond is canceled by the symmetrical... 

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