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5: Molecular Orbitals

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    A molecular orbital diagram of dihydrogen. Two atomic 1s orbitals combine to give two molecular orbitals with sigma symmetry. The lower energy sigma binding orbital has both nuclei surrounded by electron density, while the higher energy orbital possesses two lobes that are separated by a node. Molecular Orbital Theory

    Molecular Orbital (MO) Theory is a sophisticated bonding model. It is generally considered to be more powerful than Lewis and Valence Bond Theories for predicting molecular properties; however, this power comes at the price of complexity. In its full development, MO Theory requires complex mathematics, though the ideas behind it are simple. Atomic orbitals (AOs) that are localized on individual atoms combine to make molecular orbitals (MOs) that are distributed over the molecule. The simplest example is the molecule dihydrogen (H2), in which two independent hydrogen 1s orbitals combine to form the \(\sigma\) bonding MO and the \(\sigma\) antibonding MO of the dihydrogen molecule (see figure). The MO’s are also called Linear Combinations of Atomic Orbitals (LCAO).

    This page titled 5: Molecular Orbitals is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Kathryn Haas.

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