Molecular_Orbital_Tutorial

Molecular_Orbital_Tutorial - Molecular Orbital Tutorial...

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Molecular Orbital Tutorial Barry Linkletter Department of Chemistry, University of Prince Edward Island Abstract This tutorial examines a method for constructing hybrid orbitals. Combinations of atomic orbitals are referenced to the bonds of tetrahedral, trigonal planar and linear carbon centres to create the famous hybrid orbitals for SP 3 , 2 and carbon atoms. . Then these hybrid orbital are used as the basis set for creating molecular orbitals in polyatomic molecules. The energies of the orbitals are estimated and their shapes approximated using a graphical method. 1
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Tutorial #27 Molecular Orbitals Contents 1 Atomic Orbitals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 Simple Molecular Orbitals . . . . . . . . . . . . . . . . . . . . . . 5 2.1 Rules for Orbital Combinations . . . . . . . . . . . . . . . . . . . 5 2.2 The Hydrogen Molecule . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1 Interaction Energy . . . . . . . . . . . . . . . . . . . . . . 6 2.2.2 Shape of the Bonding Molecular Orbital . . . . . . . . . . 6 2.2.3 Shape of the Antibonding Molecular Orbital . . . . . . . 7 2.3 Relative Energies of Orbitals . . . . . . . . . . . . . . . . . . . . 8 2.4 Adding Circles – Graphical Orbital Combinations . . . . . . . . . 9 2.4.1 Graphical Molecular Orbitals in H 2 . . . . . . . . . . . . . 9 2.4.2 Graphical Combination of p Orbitals. . . . . . . . . . . . 10 2.4.3 Symmetries of Bonds . . . . . . . . . . . . . . . . . . . . . 10 3 Hybrid Atomic Orbitals . . . . . . . . . . . . . . . . . . . . . . . 11 3.1 SP 3 Hybrid Atomic Orbitals . . . . . . . . . . . . . . . . . . . . . 11 3.1.1 Making the Hybrid Orbitals . . . . . . . . . . . . . . . . . 12 3.2 SP 2 Hybrid Atomic Orbitals . . . . . . . . . . . . . . . . . . . . . 15 3.3 SP Atomic Hybrid Orbitals . . . . . . . . . . . . . . . . . . . . . 18 3.4 Summary (All that you really need to know about hybrid orbitals) 19 4 Molecular Orbital Systems of Organic Molecules . . . . . . . . . 21 4.1 Molecular Orbitals of Methane . . . . . . . . . . . . . . . . . . . 21 4.1.1 Energies of the Molecular Orbitals for the C–H Covalent Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 4.1.2 Shapes of the Molecular Orbitals for the C–H Covalent Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 4.1.3 All the Molecular Orbitals . . . . . . . . . . . . . . . . . . 24 4.2 Molecular Orbitals of Acetylene . . . . . . . . . . . . . . . . . . . 24 4.2.1 Energies of the Molecular Orbitals of the C–C σ bond . . 26 4.2.2 Shapes of the Molecular Orbitals of the C–C σ bond . . . 27 Barry Linkletter Version 2.0 Page 2 of 35
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Tutorial #27 Molecular Orbitals 4.2.3 Energies of the Molecular Orbitals of the C–C π -bond . . 27 4.2.4 Shapes of the Molecular Orbitals of the C–C π -bond . . . 28 4.2.5 All the Molecular Orbitals . . . . . . . . . . . . . . . . . . 29 4.3 Molecular Orbitals of Cyanide Ion . . . . . . . . . . . . . . . . . 29 5 All You Really Need To Know About Molecular Orbitals . . . . . 31 6 Advanced Topics . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 6.1 Molecular Orbitals of Polar Bonds . . . . . . . . . . . . . . . . . 33 6.1.1 Uneven combinations . . . . . . . . . . . . . . . . . . . . 33 Barry Linkletter Version 2.0 Page 3 of 35
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Tutorial #27 Molecular Orbitals 1 Atomic Orbitals All molecular orbitals (MOs) are made by combining atomic orbitals (AOs). These AOs are the familiar s and p orbitals. As we move down the periodic table we will encounter d , f and g AOs but we will leave these orbitals to the inorganic chemists who love them and concentrate on the two orbitals of most relevance to organic chemistry, the s and p atomic orbitals. 1.1 Hydrogen Most organic molecules include hydrogen. Hydrogen has only the 1 s orbital to consider. The wavefunction for the s orbital is spherical in shape with the maximum value at the centre of the sphere and the value decays exponentially as distance from the centre increases.
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Molecular_Orbital_Tutorial - Molecular Orbital Tutorial...

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