Methane tetrahedral geometry

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... 

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. 

The conformation and configuration of the polymer molecules have a great influence on the properties of the polymer component. The conformation describes the preferential spatial positions of the atoms in a molecule. It is described by the polarity flexibility and regularity of the macromolecule. Typically, carbon atoms are tetravalent, which means that they are surrounded by four substituents in a symmetric tetrahedral geometry. The most common example is methane, CH4, schematically depicted in Fig. 1.9. As the figure demonstrates, the tetrahedral geometry sets the bond angle at 109.5°. 

Fig. 4.6 Hybridization is not needed to explain bonding, e.g. the tetrahedral geometry of methane...

Therefore, AX4 molecules exhibit a tetrahedral geometry. Methane (CH4, Figure 7.10), the major component in natural gas, and chloroform (CHC13), which was once used as an anesthetic, both have tetrahedral geometries. 

In the MO picture, there will be a bonding MO (and an antibonding MO) for each bond in die Lewis structure. Furthermore, the MO model must be in accord with experimental observations. Experiments have shown that the bonds in methane are all identical, with tetrahedral geometry. Therefore, methane must have four equivalent bonding MOs, with a tetrahedral arrangement. 

Let s consider ethane, C2H6, a slightly more complex example, shown in Figure 3.8. The geometry of the molecule tells the hybridization of the atoms involved. In simple organic compounds, any atom that has tetrahedral geometry will be sp3 hybridized. Thus, both carbons are sp3 hybridized in ethane. The CFI bonds are formed in the same way as they were in methane. The CC bond is formed by the overlap of sp3 AOs on each carbon, as shown here. 

The four bonding MOs for methane have a tetrahedral geometry. 

Several views of methane. Methane has tetrahedral geometry, using four sp3 hybrid orbitals to form sigma bonds to the four hydrogen atoms. 

In this structure, there are three sigma bonds and one pair of nonbonding electrons. Four hybrid orbitals are required, implying sp3 hybridization and tetrahedral geometry around the nitrogen atom, with bond angles of about 109.5°. The resulting structure is much like that of methane, except that one of the sp3 hybrid orbitals is occupied by a lone pair of electrons. 

All of the four-coordinated molecules we have discussed so far have tetrahedral geometry around the central atom. Methane, CH4, is the most well known example. It may come as something as a surprise, then, to discover that the tetrachlorplatinum (II) ion [PtCl4]2- has an essentially two-dimensional square-planar configuration. This... 

The Cp2Zrl- C2H2-B interaction is probably electrostatic. It corresponds to an internal ion pair situation (Zrl-C2 2.600(3) A, C1-C2-B 119.2(2)° and Zrl-C2-B 155.0(2)°) analogous of the complexes described previously (see Section 3.1). It seems that this distorted C2v - methane-like coordination geometry is ca. 5 kcal moH less stable than ideal tetrahedral geometry. Certainly the gain of energy afforded by the ion pair formation is responsible for the stability of homodinuclear complex (59). 

The tetrahedral geometry usually found in 4-coordinate compounds of carbon also occurs in a different form in some inorganic molecules. Methane contains four hydrogens in a regular tetrahedron around carbon. Elemental phosphorus is tetratomic (P4) and also is tetrahedral, but with no central atom. Examples of some of the geometries foimd for inorganic compounds are shown in Figure 1-4. 

The concept of hybridization of atomic orbitals was subsequently introduced, in an attempt to interpret the difference between the actual bond angle for the water molecule and the value of 90° considered in the previous model. This concept had already been introduced to interpret, for example, the tetrahedral geometry of the methane molecule. We shall come back to this subject later in the chapter, to conclude that, although it is possible to establish a correlation between molecular geometry and hybrid orbitals, it is not correct to take the latter as the basis of an explanation of the former. This distinction is very important in teaching. 

A molecule such as dimethyl ether, CH3—O—CH3, has two different central atoms oxygen and carbon. We could picture the parts of the molecule containing the CH3 group (commonly referred to as the methyl group) as exhibiting tetrahedral geometry (analogous to methane) ... 

The valence bond description of methane, ammonia, and water predicts tetrahedral geometry. In methane, where the carbon valence is four, all the hybrid orbitals are involved in bonds to hydrogen. In ammonia and water, respectively, one and two nonbonding (unshared) pairs of electrons occupy the remaining orbitals. While methane... 

The answer is B. Methane has a tetrahedral geometry. So the hydrogen-carbon-hydrogen bond angle is closest to 109.5°. 

One commonly encountered geometry is that of a tetrahedron. Methane has the molecular formula CH4 and exists in a tetrahedral geometry with angles of approximately 109 degrees between each pair of C-H bonds. 

The next alkane is ethane, which has the molecular formula C2H5 and the structural formula CH3—CH3. This molecule may be thought of as a methane molecule with one hydrogen removed and a —CH3 put in its place. Again, the carbon bonds have a tetrahedral geometry as shown in I Figure 1.10. Ethane is a minor component of natural gas. 

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