CHEM 111 WEEK 12 Lecture Notes
CHEM 111 WEEK 12 Lecture Notes 111/40551
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This page Class Notes was uploaded by firstname.lastname@example.org Notetaker on Saturday November 28, 2015. The Class Notes belongs to 111/40551 at University of St. Thomas taught by Uzcategui-White in Summer 2015. Since its upload, it has received 11 views.
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Date Created: 11/28/15
Chemistry Week 12 Lecture Notes Chapter 10 The Shapes of Molecules 0 Building Lewis Dots 0 Example 503 2 1 Decide the central atom less electronegative Hydrogen is never the central atom S 2 Count the total number of electrons S e 0 6 x 3 18 e Charge 2e Total 26 e 3 Form a single bond between central atom and each surrounding atom 050 0 4 The remaining electrons form lone pairs to complete the octet as needed First fill the outside atoms then the central Start with the most electronegative atom first OSO 2 six dots around the O atoms and 2 on the S 0 ex CH4O 1 Central C 2 C 4e H 1 x 4 4e 0 6e Total 14 e H 3 HCOH two dots on O H 5 Multiple Bonds If there are not enough electrons for the central atom to attain an octet a multiple bond is present 9 change a lone pair into another bond Ex 502 S 6e O 6ex212e Total 18 e OSO 6 dots on O atoms and 2 on 5 atom 9 O SO 69 OSO 6 dots on 1 O and 4 on the other and 2 on S Resonance formresonance hybrid resonance structure Ex 03 OOO 69 OOO Resonance Hybrid 0 Can be depicted by more than one valid Lewis Structure 0 Resonance forms are not real bonding depictions 03 does not change back and forth 0 Delocalization of electrons 0 Fractional bond order For resonance structures bond order shared e pairs bonded atom pairs Ex bond order 03 3 shared electron pairs 2 bonded atom pairs 1 12 109 Draw lewis structures of all the important resonance forms a N02 b NOZF Formal Charges Charge an atom would have if all of the electrons were shared equally FC valence e unshared e 12 shared e Choosing More Important Resonance Forms Smaller formal charges or are preferable to larger ones The same nonzero formal charges on adjacent atoms are not preferred Avoid like charges on adjacent atoms A more negative formal charge should reside on a more electronegative atom Formal Charges vs Oxidation Numbers For a formal charge bonding electrons are shared equally b the atoms For an oxidation number bonding electrons are transferred to the more electronegative atom Exceptions for the Octet Rule 1 Molecules with electron deficient atoms Be and B EX ClBrCl 2 Odd electron species free radicals Ex 0 N O 3 Expanded valence shells Only nonmetals in period 3 or higher Ex PC5 has five bonding sites 1016 Draw lewis structures for a resonance form of each ion with the lowest possible formal charges show the charges and give oxidation numbers of the atoms Central atom less electronegative a A504 3 As 5 e 0 6 x 4 24 e Charge 3e Total 32 e Resonance form I four bonds off As to O Resonance form five bonds four single one double off As to 0 more stable Formal Charges I As FC 5 0 128 1 0 FC 6 612 2 1 ll As FC 0 O FC 0 Oxidation number As 5 0 2 1017 These species do not obey the octet rule Draw a Lewis structures for each and state the type of exception a BH3 HBH 9 electron deficient H b AsF4 expanded valence shell Molecular geometry VSEPR Valence shell electron pair repulsion quotMolecules adapt the shape that minimizes the electron pair repulsions shapes linear trigonal planar tetrahedral Electron Group Arrangements and Molecular Shape defined by both bonding and nonbonding electron groups molecular shapes 3D arrangement of nuclei joined by the bonding groups classified using the designation AXmEn A central atom E non bonding valence electron group X surrounding atom m and n integers bond angle angle formed by the nuclei of the 2 surrounding atoms with the nucleus of the central atom a linear arrangement 2 electron groups attached to the central atom bond angle 180 AX2 AXY AXE Ex HCN BeF2 C02 CN Single double triple or lone pair 1 electron group b Trigonal planar arrangement 3 electron groups attached to central atom bond angle 120 2 molecular shapes 1 trigonal planar only bonding groups AX3 2 bent or V shape lone pair of e AX2E Ex 503 PF3 N03 NBr2 trigonal Ex 502 O3 PbClZ NBr2 v shape