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Polar Bonds, Dipoles

Polar Bonds, Dipoles. Dipole Moment. HF. δ +. δ -. Dipole moment: Vector addition of the magnetic moment of polar bonds And that means……. In one bond (2 atom) molecule if the bond is a polar the molecule is polar (aka has a dipole moment)

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Polar Bonds, Dipoles

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  1. Polar Bonds, Dipoles

  2. Dipole Moment HF δ+ δ- • Dipole moment: Vector addition of the magnetic moment of polar bonds • And that means……. • In one bond (2 atom) molecule if the bond is a polar the molecule is polar (aka has a dipole moment) • In multi-bond atoms you need to look at the geometry. • Look at polar bonds and there directions • Bonds in opposite directions cancel. • Bonds in same direction add. ClF3 Total Dipole Moment is…

  3. Another Example: XeF2Cl2 Two Possible Arrangements Cl F All Polar Bonds Cancel Right/Left Cancel Part of blue forwards cancel red Total molecular dipole is back

  4. Lewis Structures: non-octet breaking For each of the Lewis stuctures we did previously, decide which bonds are polar. • CH2O 4e-+1e*2+6=12e- O C H H

  5. Lewis Structures: For each of the Lewis stuctures we did previously decide if the molecule is polar, and how many s and p bonds are present • CH2O

  6. Bonding orbital cartoon (s orbital on Oxygen left out)

  7. Lewis Structures: For each of the Lewis stuctures we did previously, decide which bonds are polar. • BH3 H B H H

  8. CO2 Decide if the molecule is polar, and how many s and p bonds are present

  9. Lewis Structures: For each of the Lewis stuctures we did previously, decide which bonds are polar. Is the molecule polar? • XeF4 • Note: Identical reasoning works for ClF4- example F F Xe F F

  10. Given the following data, does H2S have a dipole? Decide which bonds are polar, if the molecule is polar, the hybridization of the central element, how many s and p bonds are present, and what orbitals each bond is formed with Electronegativity ValuesH: 2.20 C: 2.55 S: 2.58 • C-H bond: 2.55-2.20=0.3 • S-H bond: 2.58-2.20=0.3 Yes Dipole No Dipole I don’t know

  11. Lewis Structures: O3 For each of the Lewis stuctures we did previously, decide which bonds are polar. +1 +1 O O O O O O +0 +0 -1 -1

  12. Lewis Structures: [SO3]2- For each of the Lewis stuctures we did previously, decide which bonds are polar. Is the molecule polar? -1 +0 -1 O O O +0 +0 +0 S S S -1 -1 +0 -1 -1 O O O O O O +0

  13. Microwaves: Quantum Mechanics at work. • http://phet.colorado.edu/en/simulation/microwaves • Polar water molecules are excited rotationally by microwaves • Friction heats up food • Why can’t you put metal in a microwave? • https://www.youtube.com/watch?v=XrFEaHvU7JE

  14. Challenge Questions: Chemistry doesn’t always follow our nice “rules”, lets look at some complex examples. As typical we likely won’t get to the challenge questions: Answer to be posted online after class.

  15. Lewis Structures: non-octet breaking For each of the Lewis stuctures we did previously, decide which bonds are polar. • N2O • 5e+5e+5e=16e N N O

  16. Lewis Structures: non-octet breaking For each of the Lewis stuctures we did previously decide if the molecule is polar, and how many s and p bonds are present -1 +1 +0 • N2O • Polar Molecule • But barely (0.167 debye) • For Comparison Water is 1.85 D, methanal (CH2O) is 2.33 -1 +0 +1 If calculations are ran, they are actually equal contributors.

  17. Lewis Structures: non-octet breaking For each of the Lewis stuctures we did previously decide if the molecule is polar, and how many s and p bonds are present -1 +1 +0 • N2O Bonding orbital cartoon (s orbital on Oxygen left out)

  18. Lewis Structures: non-octet breaking For each of the Lewis stuctures we did previously, decide which bonds are polar. • BH3NH3 • 3e+5e+1e*6=14e H H N B H H H H

  19. For each of the Lewis stuctures we did previously decide if the molecule is polar, and how many s and p bonds are present Lewis Structures: non-octet breaking • BH3NH3 It is POLAR but this is a strange structure and theoretical calculations or experimental evidence are required to tell. 5.49 D (for comparisons sake water is 1.85)

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