What is the difference between nonbonding and antibonding orbitals?

Nonbonding orbitals and antibonding orbitals are concepts in molecular orbital theory, which describes the distribution of electrons in molecules using mathematical models called molecular orbitals.

Nonbonding Orbitals (also known as Lone Pair Orbitals or Nonbonding Molecular Orbitals):

These orbitals contain electrons that are not involved in bonding between atoms.
Electrons in nonbonding orbitals are localized on a particular atom and do not contribute to the overall bonding in the molecule.
Nonbonding orbitals often represent lone pairs of electrons that are not shared with other atoms.
Antibonding Orbitals:

Antibonding orbitals are formed when the mathematical combination of atomic orbitals results in a destructive interference, leading to a region of higher energy compared to the original atomic orbitals.
Electrons in antibonding orbitals contribute to the destabilization of the molecule, as they are associated with higher energy states.
Antibonding orbitals weaken the overall bonding in a molecule.
In the context of molecular orbital theory, orbitals are formed by combining atomic orbitals (atomic orbitals from different atoms) to create molecular orbitals. The combination can be constructive (leading to bonding orbitals) or destructive (leading to antibonding orbitals).

For example, in a diatomic molecule (molecule composed of two atoms), when two atomic orbitals combine, they form two molecular orbitals: a bonding orbital and an antibonding orbital. The bonding orbital has lower energy than the original atomic orbitals, stabilizing the molecule, while the antibonding orbital has higher energy, destabilizing the molecule.

In summary, nonbonding orbitals are associated with electrons that do not participate in bonding, whereas antibonding orbitals are associated with electrons that contribute to the destabilization of a molecule by weakening the overall bonding.