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CHEM 1&2 Lab Manual & worksheets pg 109

CHEM 1&2 Lab Manual & worksheets pg 109 -...

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Experiment 9: VSEPR General Chemistry I and II Lab Manual Dakota State University Page 109 of 232 Polarity: By now you should know how to determine whether or not a bond is polar based on differences in Pauling's electronegativity scale (a difference in electronegativity of less than 0.5 is non-polar, between 0.5 and 1.7 is polar, and greater than 1.7 is ionic). For a diatomic molecule, the molecule is polar if the bond is polar. This is a simple enough concept, and quite intuitive, but what do we do with polyatomic molecules? Such a question is important since polarity of molecules determines the intermolecular forces between such molecules, and therefore affect many of the physical properties. Well, for polyatomic molecules, we have a few additional steps: 1. Determine the Lewis-Dot structure. 2. Determine if any of the bonds are polar or not. If there are no polar bonds, you are finished; it is a non-polar molecule. If there is even one bond, you must proceed, because it may
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Unformatted text preview: or may not be polar. 3. Determine the molecular shape using VSEPR. 4. The molecule is non-polar if it is highly symmetrical; otherwise, it is polar. In a highly symmetrical molecule, the polar bonds will cancel exactly, but how can we tell if we have a highly symmetrical molecule? Once you see it, it becomes obvious. Unfortunately, it is often difficult to see, so let's go though these rules. A molecule is highly symmetrical if ; 1. All elements bonded to the central atom are identical and we have no lone pairs, OR 2. All elements bonded to the central atom are identical and we have a linear molecule with either a trigonal planar or octahedral parent shape, OR 3. All elements on diametrically opposed sides of the central atom (exact opposit sides of the atom, so they could not "see" one another around the central element) are identical and the chemical structure is square planar....
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