CHE_106_Lecture20_2009

CHE_106_Lecture20_2009 - Chemistry 106 Lecture 20 Topics:...

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Chemistry 106 Lecture 20 Topics: Lewis Structures esonance Resonance Chapter 8.5-8.8
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Types of Chemical Bonds Three basic types of bonds Ionic Electrostatic attraction between ions Magnesium Oxide (MgO) ovalent Covalent Sharing of electrons Benzene (C 6 H 6 ) Metallic Metal atoms bonded to other metal atoms Copper (Cu)
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Writing Lewis Dot Formulas The Lewis electron-dot formula of a covalent compound is a simple two-dimensional representation of the positions of electrons in a molecule. Bonding electron pairs are indicated by either two dots or a dash. – In addition, these formulas show the positions of lone pairs of electrons.
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Writing Lewis Dot Formulas The following rules allow you to write electron-dot formulas even when the central atom does not follow the octet rule. illustrate, we will draw the structure – To illustrate, we will draw the structure of PCl 3 , phosphorus trichloride. 3 PCl
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Writing Lewis Dot Formulas Step 1: Total all valence electrons in the molecular formula. That is, total the group numbers of all the atoms in the formula. PCl 26 e - total P = [Ne]3s 2 3p 3 3 5 e - (7 e - ) x 3 – For a polyatomic anion, add the number of negative charges to this total. – For a polyatomic cation, subtract the number of positive charges from this total. Cl = [Ne]3s 2 3p 5
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Writing Lewis Dot Formulas Step 2: Arrange the atoms radially, with the least electronegative atom in the center . Place one pair of electrons between the central atom and each peripheral atom. P Cl Cl Cl Other general rules: H will make 1 single bond Halogens will make 1 single bond. 26 – 6 = 20 e - left
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Electronegativity On the periodic table, electronegativity increases… h …from left to right across a row. h …from the bottom to the top of a lumn P = 2.1 Cl = 3.0 column.
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Writing Lewis Dot Formulas Step 3: Distribute the remaining electrons to the peripheral atoms to satisfy the octet rule. l l : 20 – 18 = 2 e - left P Cl Cl Cl : : : : : :
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Writing Lewis Dot Formulas Step 4: Distribute any remaining electrons to the central atom. If there are fewer than eight electrons on the central atom, a multiple bond may be necessary . 2 – 2 = 0 e - left P Cl Cl Cl : : : : : : :
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Try drawing Lewis dot formulas for the following covalent compound. SCl 4 e - left electronegativities
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This note was uploaded on 02/09/2010 for the course CHE CHE 106 taught by Professor Korter during the Fall '09 term at Syracuse.

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CHE_106_Lecture20_2009 - Chemistry 106 Lecture 20 Topics:...

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