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Unformatted text preview: Topics for the day Administrative stuff Lewis dot structures for ions Lewis dot structures for molecules Resonance Administrative stuff Quest Homework will be posted later today and youll be notiFed by email when it is up. It will be due in two weeks time (riday 3/5) On the day it is due Ill post the sample exam Exam Two is the next Wednesday (3/10) ALEKS Objective 2 is due Monday 3/1 Today we will Fnish all the topics in Objective 2 ALEKS Objective 3 content will be on the exam, but will be due after the exam, like last time. Error correction I had said: The strength of the attraction between two oppositely charged particles can be understood using Coulombs Law . F q 1 q 2 r I was asked wasnt there an r 2 term? Coulombs Law is E q 1 q 2 r or, since Energy = Force x Distance, it can be re-written: F q 1 q 2 r 2 We care about E (lattice energy) or the strength of the bond, so the inverse dependence on r is the one that we use. I wrote the equation incorrectly the rst time. 1 2 3 Where were we? Ionic solids are very strongly bonded due to multi-ion interactions. Lattice energy is the change in energy when separated gaseous ions are packed together to form an ionic solid, and is dependent on charge and inversely dependent on bond length. A high lattice energy implies a high melting point. We deFne lattice energy as negative (energy is released when the ionic solid is formed). Although lattice energy cannot be directly measured, it can be calculated from known experimental values using the BornHaber cycle . The net dipole of a polyatomic molecule is found by geometrically combining the dipoles of all the individual bonds in the molecule. Certain geometries lead to dipole cancellation so that it is possible to have a nonpolar molecule that contains polar bonds. The localized electron (LE) bonding model describes molecules as atoms bound together by shared bonding electron pairs . Unshared electron pairs, are known as non-bonding or lone pairs . Lewis dot structures are a way to keep track of a molecules valence electrons. Write the Lewis Dot structures for these atoms: Mg, Br Your Turn Element symbol Electron confguration Number oF paired/unpaired Draw the dot structure Mg [Ne] 3s 2 3s 3p Mg Br [Ar] 4s 2 4p 5 4s 4p Br Recall that For main group elements, the valence electrons are just the s and p shells....
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- Spring '10