What primarily governs the stability of a molecule?

The bonding and antibonding characteristics of the frontier orbitals play a crucial role in determining the stability of a molecule. In molecular orbital theory, electrons are placed in molecular orbitals that are formed from the combination of atomic orbitals. These molecular orbitals can be categorized into bonding orbitals, which stabilize the molecule by promoting electron pairing and attractive interactions between atomic nuclei, and antibonding orbitals, which can destabilize the molecule if occupied.

The stability of a molecule is enhanced when there are more electrons in bonding orbitals than in antibonding orbitals. The energy difference between these types of orbitals allows for the prediction of bond order, which is defined as the difference between the number of bonding and antibonding electrons divided by two. A higher bond order indicates a more stable molecule due to stronger bonding interactions.

In contrast, while the number of valence electrons, the size and shape of atomic orbitals, and temperature can influence molecular characteristics, they do not primarily dictate the stability as fundamentally as the interactions between bonding and antibonding molecular orbitals do. Thus, understanding frontier orbital theory provides a deeper insight into the stability of molecular structures.