notes_162_Exp_1_Notes_032708

notes_162_Exp_1_Notes_032708 - Experiment 1 Chemical Models...

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Experiment 1: Chemical Models and Magnetism Chemistry 162
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Part 1: Chemical Models Zumdahl, 5 th ed., Chapts. 12-14 Objective: We will be using a molecular model kit to assist in our understanding of: – Lewis Dot Structures – Molecular Geometry Electron-pair geometry and molecular shapes Bond angles – Polarity – Orbital hybridization
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Lewis Dot Structure Review Before we can determine electron-pair geometry and molecular shape, we need to draw a Lewis Dot Structure for the molecule Steps for drawing Lewis Dot Structures 1. Sum the valence electrons from all the atoms. 2. Add or subtract electrons depending upon the overall charge on the molecule 3. Use a pair of electrons to form a bond between each pair of bound atoms 4. Arrange the remaining electrons to satisfy the duet rule for hydrogen and the octet rule for the second-row elements Adapted from Zumdahl, 5 th ed., pg. 613
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Lewis Dot Structure Examples • Consider: NH 3 Number of valence electrons Nitrogen 3 Hydrogens Total electrons 5 e - 3*(1 e - ) = 5 = 3 8 electrons + Step 1: Sum Valence Electrons Step 2: Add or subtract electrons to match overall charge Overall charge on NH 3 is 0, so no addition or subtraction of electrons is necessary.
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Lewis Dot Structure Examples Step 3: Connect pairs of atoms with an electron-pair bond N H H H Step 4: Fulfill the duet and octet rules Each bond represents 2 e - ’s 3*(2 e - ’s) = 6 e - ’s N H H H To finish this structure, we place the remaining two electrons on the nitrogen to complete its octet. 8 e - to satisfy octet 2 e - to satisfy duet
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