molecular orbital theory

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molecular orbital theory,

detailed explanation of how electrons are distributed in stable moleculesmolecule
[New Lat.,=little mass], smallest particle of a compound that has all the chemical properties of that compound. A single atom is usually not referred to as a molecule, and ionic compounds such as common salt are not made up of molecules.
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. In the simpler valence theory of the chemical bondchemical bond,
mechanism whereby atoms combine to form molecules. There is a chemical bond between two atoms or groups of atoms when the forces acting between them are strong enough to lead to the formation of an aggregate with sufficient stability to be regarded as an
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, each atomatom
[Gr.,=uncuttable (indivisible)], basic unit of matter; more properly, the smallest unit of a chemical element having the properties of that element. Structure of the Atom
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 in a molecule is assumed to retain its own electrons. Even when electrons are shared, as in the covalent bond, it is possible to identify which electron came from which atom. The molecular orbital theory, however, treats each electron as associated with the molecule as a whole. Just as a free atom has certain allowed electron orbits and energies, each molecule has its own allowed molecular orbitals. The orbitals give the probability of finding the electron at any point in space. Each orbital can hold a maximum of two valence electrons and the structure of the molecule is built up by filling the lowest energy orbitals first. The calculations involved are extremely complex, and only the simplest molecules can be treated exactly.
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References in periodicals archive ?
These conclusions inferred from the frontier molecular orbital theory are in accordance with those of the adsorbing parameter analyses.
Although, in principle, the two methods should give equivalent results, molecular orbital theory seemed to more naturally accommodate delocalized bonding and was easier to apply to large molecules.
Here the mathematical properties of eigenfunction computed upon a given basis on Hilbert-Banach spaces determine the "shift" or the "unrealistic" energies of orbitals since spanning those occupied and unoccupied alike; from the present dichotomy basically follows all critics on the Hartree-Fock formalism and of allied molecular orbital theory, Koopmans' "theorem" included; instead, there seems that such departure of the computed from the exact energy orbitals is inherent to quantum formalism and not necessary a weakness of the Hartreeformalism itself, since it will appear to any quantum manyparticle problem involving eigenproblems.
This notion was proposed by Gutman [3] and found applications in the molecular orbital theory of conjugated [pi]-electron systems [4,6].
Ligand field theory is the application of molecular orbital theory to the complexes described above.
Organic chemists need to know something about molecular orbital theory, because these days much of their work is explained in those terms.
Chapters 3, 4, and 5 present close readings of cases involving the interfaces among biology, chemistry, physics, and geometry: constructing and testing an antibody mimic, understanding the transposition of genes, and investigating benzene via molecular orbital theory. Although Grosholz is engaged by the scientific cases in their own right, especially as they illustrate the subtleties of theory reduction, she makes clear that a major motivation for including them is to emphasize commonalities with mathematical practice, and to insist that mathematics should not be considered a unique outlier when compared to the physical and biological sciences.
The experimental molecular HOMO-LUMO gap is 7.3 [+ or -] 0.2 eV for P3HT, which is consistent with 7.05 eV gap from the molecular orbital theory. These values are similar to the value of 6.4 eV estimated from the gas-phase X-ray photoelectron spectroscopy on the P3HT monomer [29].
A., 1986, Ab Initio Molecular Orbital Theory, Wiley, New York.
To investigate the reactivity of molecules and their functional groups, HyperChem uses Frontier Molecular orbital Theory. This provides estimates of the relative reactivity of different molecular substituents, regioselectivity of reactions, and site-selectivity of nucleophiles and electrophiles.

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