Unit 5 Test Review Answers

For full credit on your homework, quiz, or test, you must have ALL of the following:

·  Lewis structure

·  Molecular geometry (the name of the shape)

·  List of all IMF’s for the molecule(s)

For full credit on your test review, you must also have the 3-D drawing. I am only listing the IMF’s for the answers – if you get stuck on something, please email me for help or come by for tutoring!

  1. Nitrogen tribromide – LDF’s, dipole-dipole
  2. CH3F – LDF’s, dipole-dipole (different atoms on the ends)
  3. H2S – LDF’s, dipole-dipole
  4. Sulfur hexafluoride – LDF’s
  5. Phosphorus pentabromide – LDF’s
  6. C and O are each treated as a central atom. Try this one before you look at the answer – it’s not as hard as you think! If you still don’t get it, scroll down to the next page for the answer.
  7. Sulfur dioxide – LDF’s and dipole-dipole
  8. NO2+ - LDF’s –make sure you subtracted the electron and don’t forget to include the brackets and the charge
  9. AlF3 – LDF’s – remember that Al is a deficient atom
  10. CCl4 – LDF’s

Write “I <3 chemistry” (yes- that’s supposed to be a heart – you know you love chemistry!) on THE BACK of your paper (please don’t tell your friends – it’s the only way I know who is checking their homework).

  1. Silicon tetrahydride and germanium tetrahydride both have only LDF’s. Because silicon tetrahydride has fewer electrons (remember - TOTAL electrons, not valence electrons) than germanium tetrahydride, its LDF’s are weaker, so silicon tetrahydride has a lower melting point than germanium tetrahydride.
  2. Silicon tetrahydride has only LDF’s. Phosphorus trihydride has LDF’s and dipole-dipole IMF’s. Because LDF’s are weaker than dipole-dipole IMF’s, the silicon tetrahydride has a lower boiling point than the phosphorus trihydride.
  3. See the answer to number 6 below for the Lewis structure and IMF’s for methanol. Formaldehyde has only LDF’s (your shape should be trigonal planar). Methanol has LDF’s, dipole-dipole, and hydrogen bonding IMF’s, which are stronger than LDF’s alone. Methanol has a higher boiling point than formaldehyde, so it would be a liquid at room temperature while formaldehyde is a gas at room temperature.


6.

The shape around the C is tetrahedral. It has LDF’s and dipole-dipole IMF’s around the C (the C has different atoms on the ends).

The shape around the O is bent (remember the unshared pairs). Around the O, it has LDF’s, dipole-dipole, and hydrogen bonding IMF’s.