Orbital hybridization methane

Section 2 6 Bonding m methane is most often described by an orbital hybridization model which is a modified form of valence bond theory Four equiva lent sp hybrid orbitals of carbon are generated by mixing the 2s 2p 2py and 2p orbitals Overlap of each half filled sp hybrid orbital with a half filled hydrogen Is orbital gives a ct bond... 

The same kind of orbital hybridization that accounts for the methane structure also accounts for the bonding together of carbon atoms into chains and rings to make possible many millions of organic compounds. Ethane, C2H6, is the simplest molecule containing a carbon-carbon bond. 

Figure 1.12 The hypothetical formation of methane from an sp -hybridized carbon atom. In orbital hybridization we combine orbitals, not electrons. The electrons can then be placed in the hybrid orbitals as necessary for bond formation, but always in accordance with the Pauli principle of no more than two electrons (with opposite spin) in each orbital. In this illustration we have placed one electron...

It is important to realize that methane is not tetrahedral because carbon has sp3, hybrid orbitals. Hybridization is only a model—a theoretical way of describing the bonds that are needed for a given molecular structure. Hybridization is an interpretation of molecular shape shape is not a consequence of hybridization. 

In contrast to the four tetrahedrally oriented elliptic orbits of the Sommer-feld model, the new theory leads to only three, mutually orthogonal orbitals, at variance with the known structure of methane. A further new theory that developed to overcome this problem is known as the theory of orbital hybridization. In order to simulate the carbon atom s basicity of four an additional orbital is clearly required. The only possible candidate is the 2s orbital, but because it lies at a much lower energy and has no angular momentum to match, it cannot possibly mix with the eigenfunctions on an equal footing. The precise manoeuvre to overcome this dilemma is never fully disclosed and appears to rely on the process of chemical resonance, invented by Pauling to address this, and other, problems. With resonance, it is assumed that, linear combinations of an s and three p eigenfunctions produce a set of hybrid orbitals with the required tetrahedral properties. 

Figure 1.21 depicts some of the spatial aspects of orbital hybridization. Each sp hybrid orbital has two lobes of unequal size, making the electron density greater on one side of the nucleus than the other. In a bond to hydrogen, it is the larger lobe of a carbon sp orbital that overlaps with a hydrogen Is orbital. The orbital overlaps corresponding to the four C—H bonds of methane are portrayed in Figure 1.22. Orbital overlap along the intemuclear axis generates a bond with rotational symmetry—in this case a C(2sp )—H(l.y) CT bond. A tetrahedral arrangement of four a bonds is characteristic of sp -hybridized carbon.

The first three alkanes are methane (CH4), ethane (CH3CH3), and propane (CH3CH2CH3). All can be described according to the orbital hybridization model of bonding based on sp hybridization of carbon. 

The universally accepted argument that explains the structure of methane in terms of the well known scheme of sp orbital hybridization derives from several statements and postulates originally formulated by Linus Pauling [1], Some of these... 

The s and p orbitals used in the quantum mechanical description of the carbon atom, given in Section 1.10, were based on calculations for hydrogen atoms. These simple s and p orbitals do not, when taken alone, provide a satisfactory model for the tetravalent— tetrahedral carbon of methane (CH4, see Practice Problem 1.22). However, a satisfactory model of methane s structure that is based on quantum mechanics can be obtained through an approach called orbital hybridization. Orbital hybridization, in its simplest terms, is nothing more than a mathematical approach that involves the combining of individual wave functions for r and p orbitals to obtain wave functions for new orbitals. The new orbitals have, in varying proportions, the properties of the original orbitals taken separately. These new orbitals are called hybrid atomic orbitals. 

In addition to accounting properly for the shape of methane, the orbital hybridization model also explains the very strong bonds that are formed between carbon and... 

In Fig. 1.18 we show a calculated structure for methane where the tetrahedral geometry derived from orbital hybridization is clearly apparent. 

The carbon in methane is hybridized s (25% s character lS%p character) and the four hybrid atomic orbitals are directed toward the corners of a tetrahedron. The Is atomic orbital in each of four hydrogen atoms overlaps with one of the four... 

These bond angles are consistent with the hybridization of the atomic orbitals of the carbon atom involved in the bonds sp hybridization in methane, sp hybridization in ethene (see... 

In addition to accounting properly for the shape of methane, the orbital hybridization model also explains the very strong bonds that are formed between carbon and hydrogen. To see how this is so, consider the shape of an individual sp orbital shown in Fig. 1.14. Because an sp orbital has the character of a p orbital, the positive lobe of an sp orbital is large and extends relatively far from the carbon nucleus. 

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