che106_Lecture19

che106_Lecture19 - Chemistry 106 Lecture 19 Topics: Lewis...

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Unformatted text preview: Chemistry 106 Lecture 19 Topics: Lewis Structures Resonance Chapter 8.5-8.8 Types of Chemical Bonds Three basic types of bonds Ionic Electrostatic attraction between ions Magnesium Oxide (MgO) Covalent Sharing of electrons Benzene (C6H6) Metallic Metal atoms bonded to other metal atoms 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. 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. To illustrate, we will draw the structure of PCl3, phosphorus trichloride. 3 PCl 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. 5 e- (7 e-) x 3 26 e- total 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. P = [Ne]3s23p3 Cl = [Ne]3s23p5 3 PCl 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 Electronegativity On the periodic table, electronegativity increases from left to right across a row. from the bottom to the top of a column. P = 2.1 Cl = 3.0 Writing Lewis Dot Formulas Step 3: Distribute the remaining electrons to the peripheral atoms to satisfy the octet rule. P Cl Cl Cl : : : : : : : : : 20 18 = 2 e- left 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 . P Cl Cl Cl : : : : : : : : : : 2 2 = 0 e- left Writing Lewis Dot Formulas Try drawing Lewis dot formulas for the following covalent compound....
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che106_Lecture19 - Chemistry 106 Lecture 19 Topics: Lewis...

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