Ch 9 - Ch. 9 A. Lewis Structures a. Exceptions to octet...

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Ch. 9 A. Lewis Structures a. Exceptions to octet rule: a.i. Hydrogen : stable with only two electrons (one bond) a.ii. Boron/aluminum : stable with only six electrons (three bonds) a.iii. beryllium : stable with four electrons (four bonds) a.iv. 2 nd row elements can’t exceed octet rule because 2 d orbitals don’t exits a.v. elements in period 3 and beyond often obey octet rule, but can use empty 3 d orbitals to exceed it; no more than 10 electrons a.v.1. some examples: a.v.1.a. AsF 5 a.v.1.a.i. 40 valence electrons 20 lone pairs/bonds (first draw bonds, then draw lone pairs on fluorine b/c F can only hold 8; the rest would have to go on As) a.v.1.b. H 2 SO 4 a.v.1.b.i. 32 e-, so 16 bonds/lone pairs a.v.1.b.ii. best structure has no formal charge; exceeds octet rule b/c S has 12 valence e- a.v.1.c. BeH 2 a.v.1.c.i. 4 e-, so 2 bonds/lone pairs a.v.1.c.ii. so H—Be—H which is okay since Be only wants 4 e- a.v.1.d. XeF 2 a.v.1.d.i. 11 bonds/lone pairs a.v.1.d.ii. F—Xe—F ; 3 lone pairs on each F, then need to put rest of lone pairs on Xe (Xe and Kr take most lone pairs) a.v.1.e. NO 2 a.v.1.e.i. 17 valence electrons—8.5 bonds/lone pairs a.v.1.e.i.1. O (2 lone pairs) double bonded to N (one electron) single bonded to O (3 lone pairs) a.v.1.e.i.2. nitrogen dioxide pollution b. Drawing Lewis Dot Structures b.i. element with greatest number of covalent bond is in the center b.ii. count number of lone pairs + bonds (should be same?) b.iii. Draw single bonds b/w every element (next to each other) b.iii.1. nitrogen—common to have 3 bonds and 2 lone pairs b.iii.2. oxygen-common to have 2 bonds and 4 lone pairs? b.iii.3.
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This note was uploaded on 02/17/2012 for the course CHEM 105ALg taught by Professor Bau during the Spring '07 term at USC.

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Ch 9 - Ch. 9 A. Lewis Structures a. Exceptions to octet...

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