Final answer:
The modification to the molecular orbital model to explain B2's paramagnetism involved acknowledging the presence of unpaired electrons in the molecular orbitals. This was a significant improvement over other bonding theories and underscored the strengths of MO theory in explaining magnetic properties and electron arrangements in molecules.
Step-by-step explanation:
The molecular orbital model was modified to explain the paramagnetic nature of the B2 molecule based on experimental evidence. In molecular orbital (MO) theory, the understanding of how electrons are distributed in molecular orbitals is essential to predict the magnetic properties of molecules. Electron configuration in these orbitals follows principles like Hund's Rule and the Aufbau Principle, allowing for the distribution of electrons in a way where lower energy orbitals fill first and electrons occupy orbitals singly as much as possible, leaving room for unpaired electrons. Particularly in diatomic molecules like B2 or O2, the presence of unpaired electrons indicates paramagnetism, thereby allowing these molecules to be attracted by a magnetic field. This is a clear predictive success for the MO theory over other bonding theories like Lewis structures and valence bond theory, which cannot accurately anticipate such magnetic properties.
Paramagnetism stems from when an atom has one or more unpaired electrons, thus, can be influenced by a magnetic field. In the case of MO theory, this concept along with the electron arrangement in molecular orbitals was pivotal for explaining the unexpected paramagnetic behavior of diatomic oxygen (O2) as well as B2. Through the revised electron arrangement in the molecular orbitals, which considers energy differences and the effects of electron spin, MO theory provides a coherent explanation for the magnetism exhibited by such molecules.
Such improvements in MO theory have helped to not only describe the energies of electrons within a molecule and their probable locations but have also informed our understanding of other properties, such as electrical conductivity. Ultimately, the success of MO theory in explaining the paramagnetic property of B2 stands as one of its major triumphs, highlighting its importance in the understanding of molecular structure and properties.