L20 - The Central Themes of VB Theory Basic Principle A...

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    The Central Themes of VB Theory Basic Principle A covalent bond forms when the orbitals of two atoms  overlap  and  the overlap region, which is between the nuclei, is occupied by a pair  of electrons with  opposite spins . The two wave functions are in phase so the amplitude increases between the nuclei. Themes A set of overlapping orbitals has a maximum of two electrons that  must have opposite spins. The greater the orbital overlap, the stronger (more stable) the bond. The valence atomic orbitals in a molecule may be  different  from those  in isolated atoms. There is a hybridization of isolated atoms’ orbitals to form atomic  orbitals appropriate for molecules, called  hybrid orbitals .
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    In  Valence Bond Theory  covalent bonds between atoms are  formed when the atomic orbitals of each atom  overlap . The  overlap region corresponds to an  electron pair bond . Each H-atom has a 1 s  electron. An H 2  molecule is formed when  the 1 s  orbitals overlap. Overlap between an H 1 s  orbital and a F 2 p  orbital produces an H–F  bond. Overlap of two F 2 p  orbitals produces a F–F bond.
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    Hybrid Orbitals The numbe r of hybrid orbitals obtained equals  the number of  atomic orbitals mixed. The type  of hybrid orbitals obtained varies  with the types of atomic  orbitals mixed. Key Points sp sp 2 sp 3 sp 3 d sp 3 d 2 Types of Hybrid Orbitals
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    The  sp 3  hybrid orbitals in CH 4 .
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    When the central atom in a molecule has   four   electron groups the central atom has   sp 3   hybridization .   The  electron group  arrangement  is tetrahedral. CH 4 : Tetrahedral electron  group arrangement and  molecular shape. 4  unpaired electrons  available for bonding. NH 4 : Tetrahedral electron  group arrangment and  trigonal planar molecular  shape. 3 unpaired electrons  available for bonding. H 2 O: Tetrahedral electron  arrangement and bent  molecular shape. 2  unpaired electrons  available for bonding.
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    nd  orbitals  can participate in orbital hybridization for  atoms in period 3 or higher. Example :  P in PCl 5 . ↑↓ 3
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L20 - The Central Themes of VB Theory Basic Principle A...

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