1.3 chemical bonding_2 - UNIVERSITY OF ALBERTA INTRODUCTORY...

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1 UNIVERSITY OF ALBERTA INTRODUCTORY UNIVERSITY CHEMISTRY I (CHEM 101) CHEMICAL BONDINGS II: VSEPR Shapes of Covalent Molecules I Introduction One important aspect of covalent bonding is the shape of the covalent molecules. Understanding their shape is crucial in explaining how covalent compounds react especially in biochemical processes (e.g. the pharmacology of drug action has to do with the structure of both the drug molecule and the receptor in the body) II Molecular structure of covalent compounds (VSEPR model) Although Lewis structures provide electron assignment of a covalent compound, they do not give the true shape of the molecule. The valence shell electron-pair repulsion (VSEPR) model allows prediction of the overall geometry of covalent compounds if the number of electrons surrounding a central atom is known. Some basic definitions An electron group is a group of electron of any number that occupies a local region around an atom. An electron group can be a single, double or triple bond. It can also be a lone pair. The molecular geometry is the relative position of the atomic nuclei of the molecule . Lone pairs are not counted . The bond angle is the angle formed by the nuclei of two surrounding atoms with the nucleus of the central atom. Basic postulates of the VSEPR model : The structure of a given covalent molecule is such that the repulsion of the electron groups should be a minimum. Thus, the electron groups around a central atom are located as far away as possible from others. The repulsion between electron group decreases in the order of: Lone pair to lone pair > lone pair to bond pair > bond pair to bond pair Some important points in the construction of the molecular geometry : The geometry of a molecule is described only in terms of the arrangement of its
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This note was uploaded on 03/24/2011 for the course CHEM 103 taught by Professor Q during the Spring '11 term at American University of Antigua.

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1.3 chemical bonding_2 - UNIVERSITY OF ALBERTA INTRODUCTORY...

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