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Unformatted text preview: Topics for the day Administrative stuff Bond strength Lewis dot structures for organic molecules Exceptions to the octet rule Formal charge Valence shell electron pair repulsion (VSEPR) Administrative stuff Homework was posted Saturday afternoon, and due two weeks later (on Saturday afternoon before the exam). Topics in ALEKS are not in the homework. They will be in the sample exam (posted next week) More sample problems for practice will be provided each week. These are optional and not for credit. You really need to be working on this several times a week. Dont wait till the last moment. Notice the revision topics that are in the ALEKS objectives and Quest homework Naming ionic solids, including learning polyatomic anion names and charges (Table 2.5) Writing balanced chemical reactions and solving for mass of products given amount of reactants Solubility and net ionic reactions postponed till next exam. 1 2 3 Where were we? We learned to draw Lewis dot structures , where each pair of dots represents two of the molecules valence electrons, and there must be as many dots as the total number of bonding electrons. For a Lewis structure to be correct, all molecules must satisfy the Octet rule , other than hydrogen ( Duet rule ). To nish the structure all bonding pairs are removed and replaced by bonds. Where more than one valid Lewis structure can be drawn for the same arrangement of atoms. The actual molecule does not ip between these different options, but is the average of these resonance structures. We say the electrons are not located at any of the specic bonds, but are delocalized over all the bonds involved in the resonance. Last time I had a clicker question asking which bond was stronger (oxygen or ozone). I had forgotten that I had skipped the section on bond energies (strength) and lengths. A single covalent bond shares two electrons. Double and triple bonds share four and six electrons respectively. Multiple bond energies are higher (meaning it they are stronger - it takes more energy to break the bonds) than single bond energies. Multiple bond lengths are shorter (held tighter) than single bond lengths. Bond strength Lewis structures for organic molecules Many molecules do not have a central atom, in particular organic molecules. Organic molecules usually have a central skeleton of carbon atoms. The most common other atoms involved in organic molecules are as follows: Hydrogen Can only form one single bond. Always on the outside of the molecule surrounding the central skeleton. Halogen Forms one single bond. Always on the outside of the molecule. Oxygen Can be part of the outside of the molecule, or the skeleton....
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