L38 - Neither Lewis nor valence bond theory explain...

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Lecture 38 Housing Co-op: Molecular Orbitals Key Idea: Bonds between atoms can be described in terms of overlap of atomic orbitals. Covalent Bonding, an overview and a new look Lewis theory : atoms share electrons, the octet rule. Valence shell electron pair repulsion, VSEPR : electron “groups” repel each other. H O H Valence Bond Theory Mixing, or overlap of the half-filled atomic orbitals of the reacting atoms. 1s 1s Methane ? CH 2 Formation of hybrid orbitals : combination of three 2p orbitals and one 2s orbital of C Four sp 3 hybrid orbitals of carbon Formation of four sp 3 hybrid orbitals methane
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Ethane, CH 3 –CH 3 Rotation about a single ! -bond is relatively unrestricted C-C ! -bond Formation of three sp 2 hybrid orbitals of carbon three sp 2 hybrid orbitals of carbon in the x, y plane C Ethylene, CH 2 =CH 2 : ! and " bonds H-C and C-C ! -bonds Another look at ethylene Rotation about a double ( ! and " ) bond is severely restricted. Acetylene, HC CH Formation of two sp hybrid orbitals
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Unformatted text preview: Neither Lewis nor valence bond theory explain paramagnetism of O 2 . O Molecular orbital theory, H 2 Combination of two H 1s orbitals gives two MO orbitals of H 2 . ! 1s is the bonding orbital and ! * 1s is the antibonding orbital. Each time two atomic orbitals combine, we get two MO orbitals: bonding and antibonding Molecular orbitals formed by 2p atomic orbitals. A node containing the bond axis makes a " bond A node perpendicular the bond axis makes and antibonding orbital. Energy level diagram for MOs of second-row homonuclear diatomic molecules MO electron configurations of the second-row diatomic molecules Wrap-up points Hybrid orbitals are formed when s and p orbitals on the same atom mix together. There are two sp, three sp 2 , and four sp 3 hybrid orbitals. Molecular orbitals are formed when orbitals on two different atoms overlap....
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This note was uploaded on 04/03/2008 for the course CHEM 1A taught by Professor Nitsche during the Fall '08 term at University of California, Berkeley.

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L38 - Neither Lewis nor valence bond theory explain...

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