c8 - Theories of Covalent Bonding Valence Bond(VB)Theory...

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Theories of Covalent Bonding Valence Bond (VB) Theory - explains the interactions of atomic orbitals that create covalent bonds - explains observed molecular shapes - applied to 2 types of covalent bonds - Lewis model assumes each bonding pair is b/t 2 atoms a localized model - Tied to LS and Lewis idea of bonding - Qualitative, visual picture of molecular structure - Good for many atom molecules Molecular Orbital (MO) Theory - Explains molecular energy levels - Proposes orbitals that extend over the whole molecule, a delocalized model - derives molecular orbitals that are delocalized - combines atomic orbitals to form a set of orbitals that are the property of the molecule - - then distributed wlin these orbitals - quantitative picture lta - NI&R EJWZL'I . - - only thing that works for some molecules ' CYPCIP,~ Each complements the other
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CHM 2045 CH# 10 10.1 Orbital Bond Theories: Theories of Covalent Bonding Valence Bond (VB) Theory Molecular Orbital (MO) Theory Theories of Covalent Bonding Valence Bond (VB) Theory - explains the interactions of atomic orbitals that create covalent bonds - explains observed molecular shapes - applied to 2 types of covalent bonds - Lewis model assumes each bonding pair is b/t 2 atoms a localized model - Tied to LS and Lewis idea of bonding - Qualitative, visual picture of molecular structure - good for ground and lowest energy states Molecular Orbital (MO) Theory - Explains molecular energy levels - Proposes orbitals that extend over the whole molecule, a delocalized model - derives molecular orbitals that are delocalized
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- combines atomic orbitals to form a set of orbitals that are the property of the molecule - - then distributed w/in these orbitals - quantitative picture - High energy state model - only thing that works for some molecules - explains colors Each theory complements the other We still have a problem, e- promotion should result in two different types of bonds One for the 2s Three for the three 2p’s We do not see two different types of bonds on CH 4 To improve our model we must account for what we see a tetrahedral shape. - Imagine the four orbitals interfere with one another and produce new patterns where they intersect, much like waves in water - The new patterns are hybrid orbitals -Four atomic orbitals combine to form four identical hybrid orbitals
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- differ in only orientation with each pointing toward the corner of a tetrahedron - new orbitals are called sp 3 b/c they come form is and three p orbitals mixing - The orbitals have a node like that of p orbitals - One lobe extends further than a p orbital and one is shortened
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c8 - Theories of Covalent Bonding Valence Bond(VB)Theory...

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