Number of electrons in the anti-bonding orbitals = 0 Number of electrons in the bonding orbitals = 2 The number of bonds formed between H-atoms in hydrogen molecule may be calculated as follows: The variety of bonds formed between 2 atoms after the atomic orbitals overlap, is called the bond order and is taken as half of the difference between the number of bonding electrons and anti-bonding electrons. These energy differences have actually been calculated by spectroscopic techniques.

These values are 554kJmol -1 for boron, 846kJmol -1 for carbon, and 1195kJmol -1 for nitrogen. 15 kJmol -1, for O 2 and F 2, respectively. The reason is the high energy difference of their 2s and 2p i.e. Since πp-orbitals are not associated with mixing, so the energy of π2p y= π2p z stays unchanged.σ 2p xis raised to such an extent that it ends up being greater in energy than π bondings.Īnyways, O 2 and F 2 do not do so. All the 4 MOs get sp-character.ĭue to this mixing, their energies change in such a manner in which MOs σ2s and σ * 2s become more stable and are reduced in energy MOs as σ2p x and σ* 2p x become less stable and are raised in energy. Similarly, σ2p x and σ * 2p x MOs do not have pure p-character. hybridization of A.O.) as a result of which σ2s and σ * 2s MOs do not keep pure s-character. There is a possibility of mixing of these orbitals (i.e. This reversal is because of mixing of 2s and 2p x atomic orbitals.Īctually, the energy difference of 2s and 2p atomic orbitals is small. It has been observed that in case of B 2, C 2 and N 2, σ2p x is higher in energy than π2p y= π2p z. The diatomic molecules, such as N 2 and other -lighter molecules like B 2, C 2show slightly different energy order. The molecular orbitals of diatomic molecules such as O 2, F 2 and their negative and positive ions can be arranged in the following-increasing order of energy The energies of the molecular orbitals are determined by spectroscopic measurements. The relative energies of the molecular orbitals formed from 2s and 2p atomic orbitals in the case of homonuclear di-atomic molecules. Relative Energies of the Molecular Orbitals As there are 3 bonding molecular orbitals, the p-orbitals overlap can result in the formation of at the most three bonds: one sigma and 2 π-bonds.

The bond formed as a result of direct overlap is σ bond, while that formed as a result of sideways overlap is called a π (pi) bond. Total six molecular orbitals (3 bonding and three anti-bonding) are formed from two sets of 2p atomic orbitals. So, are likewise theπ*(2p y) andπ*(2p z) molecular orbitals. π (2p y) and π (2p z) are likewise degenerate. Considering that the 2p y and 2p z atomic orbitals are degenerate (having the very same energy), the π – molecular orbitals i.e. On the other hand, anti-bonding molecular orbitalsπ* (2p y) andπ* (2p z) have the least electron density in the π inter-nuclear area.

Order of atomic orbitals