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Unformatted text preview: CHEMISTRY & BIOCHEMISTRY (CHEM 20A) FALL 2004 LECTURE NOTES 10/1/04 Office Hours: Mon. & Wed. 3:00-4:00 p.m. @ Young 4077C T.A.: Joe Speyer ( email@example.com ) Three aspects of the course calculations, techniques, and concepts. Course schedule on V irtual O ffice H ours. Online quizzes @ www.voh.chem.ucla.edu MIDTERM #2 REVIEW Blocks of Periodic Table- Block labels (s, p, d, and f) refer to final electron to occupy orbitals (or differentiating electron), not necessarily to outermost electron Periodic Trends- Atomic Radius : 2 atoms) identical two of Radius ( o Decreases across a period due to increased effective nuclear charge ( Z eff ). o Increases down a group due to decreasing Z eff . Both trends can be explained by the following equation (especially the fact that radius increases down a group): eff Z n r 2 - electrons shell inner of #- = Z Z eff- Ionization Energy : The energy needed to remove valence electrons. A greater # of valence electrons means its harder to remove the electrons and thus the ionization energy is greater (electrons are in a lower energy state). o The overall trend is that IE i ncreases across a period due to increasing Z eff with a few anomalies (such anomalies occur between groups II and III and groups V and VI). o Decreases down a period due to increasing distance of the outermost electron , according to the relationship: 2 distance 1 attraction of Force . o Anomalies to the main trend are explained by the fact that overriding effects more than compensate for increasing Z eff . o Group II and III elements have electrons easily removed because it is further away from the nucleus (e.g. orbital- p energy higher a in e an has ,- B B Be ) o Group V and VI elements have electrons easily removed because of greater electron-electron repulsion (thus an O valence electron is easier to remove than an N valence electron because repulsions make it easier to remove an electron)....
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This note was uploaded on 05/06/2008 for the course CHEM 20A taught by Professor Scerri during the Fall '05 term at UCLA.
- Fall '05