S orbital combination

In this case since carbon has only two unpaired electrons, it seems likely that it will only form only two covalent bonds, but it is known that carbon can form four covalent bonds. To form four bonds, one electron is promoted from the 2s orbital to the 2pz orbital. Then the one 2s orbital and three 2p orbitals mix together to form four new sp3 hybrid orbitals as shown in Figure 5. So in this case of hybridization, three p and one s orbital combine to give four identical sp3 orbitals. 

These same principles can be extended to systems, such as H3+, with delocalized multicenter er-bonding derived solely from the radial s-orbital combinations. The descriptive term, in-plane aromaticity, [44] includes such cases (see Chapter 3.2.1 for further discussion). 

As the valence electrons s and p are not equivalent to one another, a molecule that is nonsymmetrical and energetically disadvantaged would result if the electrons fill their nonequivalent orbitals. Hence, one of the 2s electrons is promoted to the 2p level, which results in four half-filled atomic orbitals. The s orbital combines... 

Pauling showed that the quantum mechanical wave functions for s and p atomic orbitals derived from the Schrodinger wave equation (Section 5.7) can be mathematically combined to form a new set of equivalent wave functions called hybrid atomic orbitals. When one s orbital combines with three p orbitals, as occurs in an excited-state carbon atom, four equivalent hybrid orbitals, called sp3 hybrids, result. (The superscript 3 in the name sp3 tells how many p atomic orbitals are combined to construct the hybrid orbitals, not how many electrons occupy each orbital.)... 

The 2a MO has mainly a central atom s AO character, but is stabilized through interaction with a radial halogen p orbital combination (Hal = F, Cl, Br), and can be identified as [Pg.801]

Since we are beginning to talk about lots of different MOs, we shall need to label them with a little more thought. When s orbitals combine, the resulting MOs, both bonding and antibonding, are totally symmetrical about the axis joining the two nuclei. 

When an atom is sp hybridized, one s orbital combines with one p orbital. This allows an atom like carbon to make two double bonds or one single and... 

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