Themes > Science > Chemistry > Inorganic Chemistry > More Information about Chemical Bonding > Chemical Bonding Index > Valence Bond Theory


In the mid 1930's, the American chemist Linus Pauling developed a theory that helped to explain covalent bonding. In the valence bond model, a covalent bond is a pair of electrons of opposite spin that reside in an atomic orbital.

For example, a hydrogen atom has the electron configuration 1s1, or

H: 1s(u)
If it shares an electron with another atom, the 1s orbital fills up
H: 1s(uu)
This forms a single covalent bond between the hydrogen and the other atom.

This is true for more complex atoms as well: for example, the fluorine atom has the electron configuration

F: 1s(uu) 2s(uu) 2p(uu)(uu)(u)
Adding an electron from another atom gives a single covalent bond and a full set of orbitals
F: 1s(uu) 2s(uu) 2p(uu)(uu)(uu)

We would expect that an atom could form a bond for every unpaired electron that is has in its valence orbitals. This is basically true, but consider an atom like carbon. Using Hunds rule, we can draw out the electron configuration as

C: 1s(uu) 2s(uu) 2p(u)(u)()
This would imply that carbon can form only two bonds, but we know it forms four. To understand why this is, we have to introduce hybrid orbitals.


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