What characterizes a nonbonding orbital in terms of energy?

A nonbonding orbital is characterized by having energy levels that are equal to those of the atomic orbitals from which it is formed. These orbitals do not contribute to bond formation and generally represent electrons that are not involved in bonding interactions between atoms in a molecule. In a molecular orbital framework, nonbonding orbitals typically arise when atomic orbitals combine in a way that does not stabilize the molecule or promote bonding.

When forming molecular orbitals, bonding orbitals are lower in energy because they result from constructive interference between atomic wavefunctions, while antibonding orbitals are higher in energy due to destructive interference. Nonbonding orbitals, on the other hand, do not exhibit this energetic shift towards either stability or instability since they are not significantly involved in the bonding process and therefore maintain energy levels similar to the original atomic orbitals.

This understanding underscores the unique role nonbonding electrons play in the chemistry of a molecule, influencing properties such as molecular geometry and reactivity without energetically favoring or disfavoring bond formation.