Involves delocalized electrons can be used to

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Involves delocalized electrons Can be used to describe reactions – Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) A different approach compared with Valence Bond Theory, which uses localized hybrid orbitals. mix first, then bond
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6 Built out of atomic orbitals Electrons are allowed to delocalize throughout the molecule Usually, we can treat σ and π separately; π has higher energy than σ Highest Occupied Molecular Orbitals are electron donors (Lewis Base — has a high energy HOMO) Lowest Unoccupied Molecular Orbital are electron acceptors (Lewis Acid — has a low energy LUMO) Molecular Orbital Theory The molecular orbitals (MOs) for the molecules that follow are constructed out of the atomic orbitals (AOs) of the valence shell. We will use the one 2 s and the three 2 p orbitals for second row elements. Hydrogen provides only its 1 s orbital. Count the electrons that each element provides and fill the orbitals from lowest to highest. You will then have your Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO). Molecular Orbital Theory: Some Examples
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7 Nitrogen (N 2 ) by energy levels: 10 valence electrons; 5 from each N 3 2p 3 2p 2s σ s σ s * π π * 2s σ p σ p * N N N 2 bond order = 3 Nitrogen : 10 valence electrons (5 from each nitrogen) σ s σ s * σ p σ p * π π *
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