1.3 chemical bonding_2 ppt

1.3 chemical bonding_2 ppt - Introductory University...

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Unformatted text preview: Introductory University Chemistry I Unit 2 Chemical Bondings II (VSEPR) Introduction • An important aspect of covalent bonding is the shape of the covalent molecules. • Understanding their shape is important – For drug design – For understanding metabolism The Shape of Covalent Molecules • Lewis structures do not give the true shape of a covalent molecules he lence ell ctron ir pulsion • The V alence S hell E lectron-P air R epulsion (VSEPR) model – predicts molecular geometries 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 . he olecular shape olecular geometry the X Y X Y X An electron group X Y • The molecular shape ( molecular geometry ) is the relative position of the atomic nuclei of the molecule. • The bond angle is the angle formed by the nuclei of two surrounding atoms with the nucleus of the central atom. A B B Bond angle Basic postulates of the VSEPR model : • The repulsion of the electron groups should be minimized . Electron groups around a central atom is located as far away as possible from the 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 A A X A X X > > Repulsions Some important points in the construction of the molecular shape : • To determine the molecular shape (molecular geometry) - only the arrangement of bond pairs is considered. Never take lone pairs into consideration. • Multiple bonds are treated as a single bond in considering the structure. Electron group arrangement and molecular shapes Two electron group AB 2 With no lone pair in the central atom Shape: linear (bond angle =180 o ) A B B Example: BeCl , CO Example: BeCl 2 , CO 2 C O O Be Cl Cl Linear structure: CO 2 A B Three electron group AB 3 With no lone pair in the central atom : Shape: trigonal planar , bond angle = 120 o B B B F F F C O O O Example: BF 3 , CO 3 2-Trigonal Planar structure: CO 3 2-With lone pair in the central atom...
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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 ppt - Introductory University...

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