A - Electronic energy levels in organic solids

Summary

Bonding in organics

Carbon has an atomic number of six and a valency of four. Its electron configuration is 1s², 2s², 2p², i.e., the inner s shell is filled and the four electrons available for bonding are distributed two in s orbitals and two in p orbitals. The s orbital is spherically symmetrical, as shown in figure A.1(a), and can form a bond in any direction. In contrast, the p orbitals, figure A.1(b), are directed along mutually orthogonal axes and will tend to form bonds in these directions. When two or more of the valence electrons of carbon are involved in bonding with other atoms, the bonding can be explained by the construction of hybrid orbitals by mathematically combining the 2s and 2p orbitals. In the simplest case, the carbon 2s orbital hybridizes with a single p orbital. Two sp hybrids result by taking the sum and difference of the two orbitals, as shown in figure A.2, and two p orbitals remain. The sp orbitals are constructed from equal amounts of s and p orbitals; they are linear and 180° apart.

Other combinations of orbitals lead to different hybrids. For example, consider three groups bonded to a central carbon atom. From the 2s orbital and two p orbitals (e.g., a p_x and a p_y), three equivalent sp²hybrids may be constructed.