Types of Molecular Orbitals(bonding, antibonding)

A molecular orbital is a method of creating bonds where the orbitals encompass the entire molecule rather than being located between atoms. They are the result of combinations of atomic orbitals. Since orbitals are wave functions, they can combine constructively to form bonding molecular orbitals or divide to form antibonding molecular orbitals.  

Molecular orbitals form when atomic orbitals with similar energies and correct symmetry can overlap. Atomic orbitals of different energies or wrong spatial orientation (orthogonal) do not combine and are called bondless orbitals. 

Orbitals 

Orbitals represent the probability of finding an electron at any random location. These orbitals correspond to different energies. Electrons in orbitals have a certain amount of energy. 

Here is how Quantum mechanics best describe orbits.

Molecular orbitals are formed due to the overlapping of two atomic orbitals occupied by a pair of electrons.

Atomic orbitals represent the region just outside the atom’s nucleus where the probability of finding electrons is greatest (95 per cent). 

Molecular Bond Formation

Molecular orbitals arise from the enabled proximity between atomic orbitals, which are sanctioned if their ideal symmetries (as determined by group theory) are amicable with each other.

Molecular Bond Type

When atomic orbitals interact, the resulting molecular orbitals can be of three types: bonding, antibonding, and nonbonding.

Bonding Molecular Orbital

Bond orbitals are commonly used in molecular orbital theory to elaborate the interactions between the atomic orbitals of two or more atoms in a molecule.

The energy of bonding molecular orbitals is lower than the atomic orbitals to which they are bound.

The MO diagram for dihydrogen

Antibonding Molecular Orbital

In chemical bonding theory, an antibonding orbital is a molecular orbital that weakens the chemical bond between two atoms and helps increase the energy of a molecule relative to a single atom

Antibonding interactions between atomic orbitals are destructive (out-of-phase) interactions, nodal planes where the wavefunction of the antibonding orbitals between two interacting particles is zero

Antibonding molecular orbitals have higher energies than the atomic orbitals to which they bind

Non-Bonding Molecular Orbital

A non-bonding orbital, also known as a non-bonding molecular orbital, is a molecular orbital whose electron occupation does not increase or decrease the order of the bonds between the atoms involved. Therefore, it cannot overlap and interact with the s-type valence orbital on the hydrogen atom.

Molecular Orbital Diagrams

The molecular orbital diagram is a qualitative description tool that explains chemical bonds in molecules, usually in terms of molecular orbital theory, in particular, linear combinations of atomic orbitals.

A molecular orbital diagram is a diagram of molecular orbital energy levels, shown as a short horizontal line in the middle, flanked by constituent atomic orbital energy levels for comparison, with d energies increasing from bottom to top. Lines, usually dashed diagonal lines, connect the molecular orbital levels to the atomic orbital levels of which they are composed.

Degenerate energy levels are usually displayed side by side. According to the Pauli exclusion principle, the correct atomic orbital and molecular orbital energy levels are filled with electrons, represented by small vertical arrows whose orientation indicates the electron’s spin.

According to Aufbau’s principle, we predict the distribution of electrons in these molecular orbitals by filling the orbitals in the same way as atomic orbitals.

Molecular Orbital Theory

For simplicity, we will consider the interaction of orbitals containing valence electrons to generate molecular orbitals. The wave functions of ‘hydrogen atom A’ and ‘hydrogen atom B’ can interact constructively or destructively. The goal of molecular orbital theory is to describe molecules similarly to how we describe atoms, that is, in terms of orbitals, orbitals diagrams, and electronic configuration. 

The molecular orbital theory explains the chemical bonds explain the paramagnetism of oxygen molecules. This also explains binding in many other molecules, such as octet line violations and many more molecules with more complex bindings (beyond the scope of this paper) that are difficult to describe with Lewis structures. In addition, it provides a model to describe the energies of electrons in molecules and the possible locations of those electrons.

Antibonding vs Bonding Orbitals

Most of the time, electrons between the two nuclei are placed in bonding orbitals, while electrons outside the two nuclei, most of the time are placed in antibonding orbitals. The electron density between nuclei in bonding orbitals increases while the electron density in antibonding orbitals decreases. When a molecule is between two nuclei, placing electrons in the bonding orbitals stabilises the molecule. Conversely, placing electrons in antibonding orbitals reduces the stability of the molecule. Depending on the energy level of the orbital, electrons fill. They will fill the lower energy orbitals first; then they will fill the higher energy orbitals. If the obtained bond order is zero, it means that the molecule is too unstable and, therefore will not exist.

Conclusion

The amalgamation makes molecular orbitals of atomic orbitals of bonded atoms. Thus, electron arrangements are found in different atomic orbitals, usually associated with other atomic nuclei. The molecular orbital theory describes the behaviour of electrons in molecules in terms of combinations of atomic wave functions. The resulting molecular orbitals can span all atoms in the molecule. 

The molecular orbital theory functions on the idea that atomic orbitals join to make molecular orbitals. Since the electron density of each atom is distributed throughout the molecule, the energy of the electrons is reduced. Overlapping atomic orbitals effectively produce stable molecular orbitals.