Question

What three interactions aid in producing an antibonding molecular orbital?

Answer 1

In chemical bonding theory, an antibonding orbitalis a type of molecular orbital (MO) that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms. Such an orbital has one or more nodes in the bonding region between the nuclei. The density of the electrons in the orbital is concentrated outside the bonding region and acts to pull one nucleus away from the other and tends to cause mutual repulsion between the two atoms.This is in contrast to a bonding molecular orbital, which has a lower energy than that of the separate atoms, and is responsible for chemical bonds.

Both the antibonding orbitals and the bonding ones are obtained in the same way and in the same operation: when the AOs are combined to obtain the MO.

When the combination of two atomic orbitals is generated to obtain molecular orbitals, the most common procedure is to use the LCAO method.

That means that we are going to do a linear combination of two wave functions (the AOs) and that, therefore, we will get two new wave functions (the MOs). One such combination stabilizes the electrons, while the other gives rise to a higher energy.

Therefore, the first will be a bonding orbital, i.e. a molecular orbital in which the electrons will have an energy less than the sum of the energies they had in the separated AOs. In contrast, the second MO obtained will be the antibonding orbital, in which the electrons will have an energy greater than the sum of the energies that they had separately