# I do not know what antibonding means and why those types of molecular orbitals are highly energetic. Please explain me with easiest way so that I can understand?

##### 1 Answer

*This is based on the amount of nuclear repulsion you get if you form a node within a molecular orbital. The more nuclear repulsions, the greater the energy of the overlap and the less favorable it is.*

The **linear combination** (sum of product terms) **of atomic orbitals** (AOs) gives molecular orbitals (MO). If for example we take two

#psi_"b" = 1s_A + 1s_B#

#psi_"a" = 1s_A - 1s_B# where

#psi_b# represents the bonding#sigma_"1s"# MO,#psi_a# represents the antibonding#sigma_"1s"^"*"# MO, and#1s# simply represents a#1s# AO.#A# and#B# simply differentiate one#1s# AO from the other.

This can also be pictorially represented as:

When two AOs overlap in-phase, like for **electron density**, which means that there is a *greater capacity* for the electron to be found in between the two orbitals.

Normally with a **bonding** MO, the increased likelihood of electrons appearing in between two atoms **promotes the interaction of the nuclei with the electrons, not with each other.**

On the other hand, when two AOs overlap out-of-phase, like for **no electron density**. So, you cannot find any electrons in the node (like a void/hole).

Having a region of no electron density within an **antibonding** MO means that there can be no electrons for the nuclei to interact with, and so **the nuclei interact repulsively with each other**, increasing the energy of the orbital overlap.

*The more they try to overlap, the greater the nuclear repulsions become and the higher in energy the overall antibonding MO becomes.*