Conditions for the combination of atomic orbitals
Conditions for the combination of atomic orbitals
The linear
combination of atomic orbitals to form molecular orbitals takes place only if
the following conditions are satisfied:
1. The
combining atomic orbitals must have the same or nearly the same energy. This means that 1s orbital can
combine with another 1s orbital but not with 2s orbital because the energy of
2s orbital is appreciably higher than that of 1s orbital. This is not true if
the atoms are very different.
2. The
combining atomic orbitals must have the same symmetry about the molecular axis. By convention z-axis is
taken as the molecular axis. It is important to note that atomic orbitals
having same or nearly the same energy will not combine if they do not have the same
symmetry. For example, 2pz orbital of one atom can
combine with 2pz orbital of the other atom but not
with the 2pz or 2py orbitals
because of their different symmetries.
3. The
combining atomic orbitals must overlap to the maximum extent. Greater the extent of overlap, the
greater will be the electron-density between the nuclei of a molecular orbital.
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