Then, by examining the particles that are in the furthest orbits, the amount of attraction that one has for the other can become a predictor of a chemical reaction. The total energy remains constant, however, so the loss of potential energy is compensated by an increase in kinetic energy. The positive potential energy of an electron will become more negative as it moves toward the attractive field of the atom’s nucleus. This is where FMO comes to help the reaction process of the positive and negative energies which exist in the orbits of every atom. This would cause it to collapse, which means a different orbital process must take place. Using classical mechanics, electrons would eventually have their orbits decay and spiral into the nucleus of the atom. That means the lowest possible energy that an electron can take is analogous to the fundamental frequencies of a wave on a string. Atoms can share up to three electrons, forming singular, double, and triple bonds in the process.Įlectrons orbit the nucleus, but not in the way that the Earth orbits the sun. When two atoms can share two electrons, then you’ve constituted a chemical bond. Molecules can begin to form bonds when they are able to share an electron. Why We Need the Frontier Molecular Orbital Theory It would be followed by HOMO +2 and so forth. The next highest occupied molecular orbital, for example, would be designated HOMO +1. HOMO stands for “highest occupied molecular orbital.” LUMO stands for “lowest unoccupied molecular orbital.” The “high” and “low” components of the description refer to the energies that are present.ĭifferent degrees of energy are present within these components. This is where the HOMO and LUMO interactions come into play. This means they tend to have the highest and lowest energies, whether they are occupied or unoccupied. These outer-edge orbitals, on the “frontier” of the molecule, are the ones that tend to be the most spatially delocalized. Why Is It Called the “Frontier” Molecular Orbital Theory?įrontier molecular theory looks at the orbitals which are at the outer edges of a molecule instead of all the orbitals that may exist. The occupied orbitals of one molecule and the unoccupied orbitals of the other molecule, with specificity to the HOMO and LUMO interactions, cause an attraction between the two molecules.īecause of these observations, the frontier molecular orbital theory can explain how the interactions of HUMO in one species are naturally attracted the LUMO of another species.The positive charges of one molecule with attract the negative charges of the other molecule.When there are occupied orbitals of different molecules, they will repel one another.Fukui made three primary observations for his theory as he watched two molecules interact with one another. The foundation of the theory is found by looking at the frontier orbitals, which are the HOMO and LUMO interactions. He would become the first Asian scientist to win a chemistry-based Nobel Prize. First published in the Journal of Chemical Physics by Kenichi Fukui in 1952, it is a theory of reactivity that would eventually help Fukui share a Nobel Prize in Chemistry for reaction mechanisms. But this concept of bond order fails in some cases like in the case of polyatomic molecules, it is only suitable for diatomic molecules.Frontier molecular orbital theory is an application of the MO theory that describes the interactions of HOMO and LUMO interactions. Molecular orbital theory describes the existence of molecules on the basis of bond order. $ $ describes that the oxygen molecule is paramagnetic in nature. From the above diagram we can see that the electronic configuration for the oxygen is as follows:
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