Question

Please can you explain in detail with diagrams what a bonding and an anti-bonding orbital are, and what the difference is between them?

Answer 1

Atomic orbitals combine to form new molecular orbitals, molecular orbital theory is concerned with this phenomenon. It describes this process using quantum mechanics. Unlike previous theories, this one did not consider electrons as assigned to individual bonds between atoms, rather they were considered to be moving under the influence of the nuclei of the whole molecule.The atomic orbitals undergo linear combination to form bonding and anti-bonding orbitals. Below are two simple examples of H₂ and He₂ molecules.

H₂ molecule

He₂ molecule

The bonding orbitals are at a lower energy than the anti-bonding orbitals, so they are the first to fill up. They are created via the linear combinations of atomic orbitals (LCAOs) approximation, i.e. from the sum and the difference of two atomic orbitals. By figuring out the molecular orbitals, it is easy to calculate bond order.

Below are some differences between bonding and anti-bonding orbitals.

• Bonding orbitals have a lower energy than anti-bonding orbitals.
• Electrons in Bonding orbitals spend most of their time between the nuclei, whereas the ones in anti-bonding orbitals spend most of their time away from the nuclei.
• Bonding orbitals get filled before anti-bonding orbitals. Their energy is less than the energy of the original orbitals whereas the energy of anti-bonding orbitals is more than that of the individual orbitals.
• Placing an electron in the bonding orbital stabilizes it, whereas placing it in the anti-bonding orbital de-stabilizes it.

When two 1s orbitals combine they form bonding orbital and anti-bonding orbital . Similarly two 2pz orbitals combine to form bonding orbital and anti-bonding orbital . Below are their figures