11: Molecular Orbital Theory (original) (raw)
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Foundations of Chemistry, 2017
The present work is a comment of a recent paper by Fortin and coauthors (Fortin et al. in Found Chem 19:43-59, 2017) in which the authors propose the introduction of Bohmian mechanics (BM) in the philosophy of chemistry and the use of standard quantum mechanics (SQM) as a mere instrument of prediction. This way would allow overcoming the obstacles found in linking molecular chemistry and quantum mechanics. Starting from some remarks on the orbital concept, we highlight and discuss some general issues that need to be taken into account when two scientific theories coexist within the same investigation field, i.e. SQM and BM. Keywords Bohmian mechanics Á Standard quantum mechanics Á Orbital concept Á Quantum electron state Á Underdetermination Á Pragmatic view of theories Commentary The work by Fortin, Lombardi and Martinez Gonzales is extremely relevant and raises some general issues that deserve to be underlined. The authors propose that the introduction of Bohmian Mechanics (BM) in the philosophy of chemistry might overcome, or at least decrease, the obstacles found in linking molecular chemistry and quantum mechanics: ''At this point, it is worth clearly stressing that the arguments presented above belong to the field of the foundations and the philosophy of chemistry […] the conceptual difficulties
Molecules
This essay describes the successive births of valence bond (VB) theory during 1916–1931. The alternative molecular orbital (MO) theory was born in the late 1920s. The presence of two seemingly different descriptions of molecules by the two theories led to struggles between the main proponents, Linus Pauling and Robert Mulliken, and their supporters. Until the 1950s, VB theory was dominant, and then it was eclipsed by MO theory. The struggles will be discussed, as well as the new dawn of VB theory, and its future.
The Old Quantum Theory for H2+: Some Chemical Implications
Journal of Chemical Education, 2006
In this article we review the description of the classical motion of an electron in a diatomic molecule such as H 2 + . The motion, treated according to the tenets of the "old quantum theory", is based entirely on the classical electron trajectories. As documented below, recent work has shown that the failure of the approach is not as profound as might once have been thought. The motivation for such studies is the insight into the quantum behavior offered by the classical viewpoint. Chemistry students are often exposed to Bohr atomic orbits several times in a curriculum. Exposure to the molecular analogs in the appropriate context complements the atomic case and can even serve to reduce some of the mysticism often associated with chemical bonding. The examples presented here augment those currently available for discussing bonding and superposition of wave functions from a different and more easily understood perspective. As such, they may seem more pertinent to many students and prepare the way for subsequent examples.
Valence Bond and Molecular Orbital: Two Powerful Theories that Nicely Complement One Another
Journal of Chemical Education, 2021
Introductory chemistry textbooks often present valence bond (VB) theory as useful, but incorrect and inferior to molecular orbital (MO) theory, citing the electronic structure of O 2 and electron delocalization as evidence. Even texts that initially present the two theories on equal footing use language that biases students toward the MO approach. However, these "failures" of VB are really just misconceptions and/or misapplications of the theory. At their theoretical limits, both VB and MO are equivalent; they simply approach that limit from different sides. Certain concepts may be easier to grasp with one theory or the other so that having a commanding knowledge of both is extremely beneficial. However, presenting one theory as superior to the other suppresses the ability to look at a problem from both sides and is therefore detrimental to students and the whole of chemistry. It is time for VB and MO to be taught on equal footing like the complementary theories they are.
On the electron-pair nature of the hydrogen bond in the framework of the atoms in molecules theory
2003
Delocalization indices, as defined in the atoms in molecules theory, have been calculated between hydrogen-bonded atoms in 20 molecular complexes that are formed between several H-donor and acceptor molecules. In general, the delocalization index associated to an intermolecular hydrogen bond depends on the interaction energy of the complex, but also on the nature of the H-donor and acceptor atoms.