Assignment_1_Review_Answers

Assignment_1_Review_Answers - CHM 2120 Assignment #1...

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CHM 2120 – Assignment #1 ANSWERS In this assignment: - Lewis structures, formal charge - Electronegativity, dipoles - Resonance - Acid/base 1. Draw the following molecules as full Lewis structures. Many molecules below possess a charge that is not shown—calculate the formal charge on each atom and indicate the location of the charge where applicable. Hint: each atom has a full octet, so start by adding electrons to each atom to complete its octet. The only atoms we will encounter in this course that lack an octet are carbon (a carbocation lacks an octet) and metals (B, Al, Mg, Li, etc). SH 2 example: C C C C C S H H H H H H H H H H H H H Formal charge (FC) = # valence electrons in neutral atom - # bonds - # lone electrons For the carbons: FC = 4 - 4 - 0 = 0 (the carbons are all neutral in this molecule) For the sulfur: FC = 6 - 3 - 2 = +1 (so a "+" is placed beside the S) C C O C C C C C O C H C C C C O C C C O C C C C C N C C C C C N C H a) b) c) f) g) h) H H H H H H H H Note: remember to include the lone pairs! C C C C C H H H H H H H H H H H H H H H HH H H FC=6-1-6=-1 H H H H H C H H H H H H H H C O C C C C C H H H H H H H H H H H H H H H FC = 5 - 3 - 2 = 0 FC = 6-3-2=+1 FC=5-4-0=+1
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Assignment 1 – Review Answers 2 C C C C C O H C C C O C C C C C C C C C C C C O O N C C H H HH H H H H H H H H H H H H H H H H H H H H H H H H H C C C C H H H H H H H H H C C C C C C H H H H H H H H H d) e) i) j) k) FC = 6-3-2=+1 FC = 6-3-2=+1 all atoms are neutral all atoms are neutral
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Assignment 1 – Review Answers 3 2. Circle the plausible structures and put an “X” through the impossible structures below: C C C C Me C N N N N O O O O 2 + B B B 2 - Lone pairs were added to complete theocte tandsa t is fytheFC. FC=O Possesses an empty "p" orbital FC = -1 (3-4-0) No lone pairs *Pentavalent (5 bonds) to C, N, or B is impossible too unstable 3. For the following bonds, a. Show the direction of the dipole moment using two methods. b. Is the bond ionic or polar covalent? Example: C-H CH δ - δ + Method 1: δ - and δ + indicate PARTIAL negative and PARTIAL positive charges; the formal charge of each atom is ZERO. Method 2: an arrow points toward the more electronegative atom; there is a "+" sign at the base of the arrow, under the more electropositive atom
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Assignment 1 – Review Answers 4 i. C-B ii. Li-C iii. Mg-C iv. Li-O v. C-Br vi. C-N vii. N-Br viii. O-Cl ix. O-H x. S-H xi. N-H δ δ + δ δ + δ δ + δ δ + δ δ + δ δ + δ + δ δ + δ δ + δ δ + δ δ + δ All the bonds are polar covalent with the exception of the Li-O bond (ionic).
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Assignment 1 – Review Answers 5 4. For the following molecules: a. Draw the important resonance forms using arrows to show the movement of electrons b.
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This note was uploaded on 01/25/2011 for the course SCIENCE CHM2120 taught by Professor Tonydurst during the Spring '08 term at University of Ottawa.

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Assignment_1_Review_Answers - CHM 2120 Assignment #1...

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