Gen Chem Week of 4/18-22/2016
Gen Chem Week of 4/18-22/2016 CHEM - 10060 - 001
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This 8 page Class Notes was uploaded by Nick Manning on Sunday April 24, 2016. The Class Notes belongs to CHEM - 10060 - 001 at Kent State University taught by TBA in Fall 2015. Since its upload, it has received 9 views. For similar materials see GENERAL CHEMISTRY I in Chemistry at Kent State University.
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Date Created: 04/24/16
CHEM I NOTES 8 LEWIS STRUCTURES REPRESENTING COVALENT SPECIES Resonance hybrid- weighted average of its contributors - Only one real structure, can be shown by two or more valid structures though - Delocalized e- The arrow shows that these two are valid and mean the same thing, but have differences So the only difference is on what atoms the bonds are made. In finding which model contributes the most when there are more than just two elements (how the professor will ask questions about this) there are three steps/rules. 1.) Full octets are preferred 2.) The model with fewer non-zero formal charges is more likely to be used 3.) Prefer to carry the negative Formal Charge on the atom with the highest Electronegativity So which model would most likely contribute to the correct structure of the example above? #3 would, it matches the criteria the closest. ELECTRON DEFICIENT SPECIES - Neutral covalent compounds of Be, Al, and B often have e- deficient central atoms. These species often occur when: o Odd-Electron Series (odd group #) o In radical (one or more unpaired e-) elements, such as NO 2 o Expanded Valence Shell (more than 8 atoms on the valence shell) Elements from Period 3 and up may have this MOLECULAR GEOMETRY Molecular shape - Lewis structures are FLAT depictions of molecules, which are really 3D. - Valence Shell Electron Pair Repulsion (VSEPR) o e- groups in valence shell repel each other & arrange themselves to maximize distance from each other COUNTING ELECTRON GROUPS A lone pair counts for one e- group, all bonds (single double and triple) all count as one group, and single e- count for one e- group. Lone pairs take up more space than bonds There are 6 main formations of molecules we will look at, however there are variations listed in the final picture. 1) Linear - 180ᵒ bw bonds, three e-groups 2) Trigonal Planar- 120ᵒ between bonds, four elements total, 3 e- groups 3) Tetrahedral- 4 groups 4) Trigonal Bypyramidal – 5 groups 5) Octahedral – six e- groups 6) Square Pyramidal – six e- groups, one lone pair MOLECULAR POLARITY -covalent species are polar if there is an uneven distribution of e-. -⧍EN > .4 but less than 1.7 for ONE BOND ONLY - o find polarity of a system of more than one bond, look at the polarity of each bond - For every polar bond add a dipole arrow in the direction of the more electronegative element -If the dipoles cancel (point in the exact opposite direction) then the molecule is nonpolar, if they do not cancel then it is overall polar.
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