www.tutor-homework.com

# How To Tell if a Molecule Is Polar or Non-Polar?

These are problems using 3D molecules run in the application Jmol to help you visualize the molecule to determine if it is polar or non-polar.

Step 1: Draw the Lewis structure. Note the number of electron regions around the central atom, and of these which are bonding or lone pairs (non-bonding pairs) Step 2: Use this info to determine the 3D geometry of the molecule. You do this by remembering "VSEPR". Valence Shell Electron Pair Repulsion theory; around the central atom all regions of electrons repel each other to get as far away from each other as possible while pivoting around the central atom. Note that double bonds and triple bonds count as a single region of electrons. Step 3: Determine if the molecular is polar or non-polar - a molecule is (i) non-polar if the charge distribution is symmetric and (ii) polar if the charge distribution is asymmetric (not symmetric).

The Decision Process:
After you draw the molecule in 3D representation using VSEPR rules, if the molecule has symmetry around the central atom, the bond dipole moments will "cancel out" (like pulling in opposite directions) and the molecule will therefore be non-polar.

However, if the molecule is asymmetric, the bond dipole moments won't "cancel out" and the molecule will have a net dipole moment and the molecule is therefore polar.

To really understand how to do this, the Lewis structure is only the first step. You need to consider the molecule in 3D (three dimensions). If you click on the example molecules (where it says 3D view) below you'll get a better understanding of why some molecules are polar and some not.

Note: molecules with two atoms are not shown in these examples; they are always linear with sp hybridization. If the atoms are the same, the molecule is non-polar molecule; if the atoms are different, the molecule is polar.

What good is this?
The polarity of a molecule will tell you a lot about its solubility, boiling point, etc. when you compare it to other similar molecules. Water, for example, is a very light molecule (lighter than oxygen gas or nitrogen gas) and you might expect it would be a gas based on its molecular weight, however the polarity of water makes the molecules "stick together" very well. And it's a good thing, because if water was not so polar, we would certainly not be here.

VSEPR Rules: Table of Molecular Geometry,    Molecular Polarity Problems (with 3D solutions!).

VSEPR Rules:
 Electron and Molecular Geometry On Central Atom. Click for Print View. Electron Regions, shape, & hybridization Bonding Regions Lone Pairs Electron Region Geometry Molecular Geometry Examples 2     sp 2 0 linear linear BeF2, CO2 1 1 linear CO, N2 :N≡N: :C≡O: 3     sp2 3 0 trigonal planar trigonal planar BF3, CO32- 2 1 bent O3, SO2 1 2 linear O2 4     sp3 4 0 tetrahedral tetrahedral CH4, SO42- 3 1 trigonal pyramidal NH3, H3O+ 2 2 bent H2O, ICl2+ 1 3 linear HF, OH- 5     sp3d 5 0 trigonal bipyramidal trigonal bipyramidal PF5 4 1 seesaw SF4, TeCl4, IF4+ 3 2 T-shaped ClF3 2 3 linear I3-, XeF2 6     sp3d2 6 0 octahedral octahedral SF6, PF6-, SiF62- 5 1 square pyramidal BrF5, SbCl52- 4 2 square planar XeF4, ICl4-

# Molecular Geometry & Polarity Example Problems

Remember!... Step 1: Draw the Lewis structure, Step 2: Draw the 3D molecular structure w/ VSEPR rules,
Step 3: Use symmetry to determine if the molecule is polar or non-polar.
Click on the molecule's name to see the answer, but first try to do it yourself!

 1. SF5Cl - Sulfur Monochloride Pentafluoride 2. SOF4 Sulfur Monoxide Tetrafluoride 3. SF6 - Sulfur Hexafluoride 4. SF4 - Sulfur Tetrafluoride 5. ICl5 - Iodine Pentachloride 6. PCl5 - Phosphorus Pentachloride 7. XeCl2 - Xenon Dichloride 8. XeF4 - Xenon Tetrafluoride 9. AlCl3 - Aluminum Trichloride 10. CS2 - Carbon Disulfide 11. BeI2 - Beryllium Diiodide 12. SeF6 - Selenium Hexafluoride 13. AsF5 - Arsenic Pentafluoride 14. NOCl - Nitrosyl Chloride 15. PO(OH)3 - Phosphoric Acid 16. SO2Cl2 - Sulfuryl Chloride 17. NOCl - Nitrosyl Bromide 18. BrF3 - Bromine Trifluoride 19. ClF5 - Chlorine Pentafluoride 20. BCl3 - Boron Trichloride 21. SiH4 - Silicon Tetrahydride 22. BeBr2 - Beryllium Dibromide 23. PF5 - Phosphorus Pentafluoride 24. BrF5 - Bromine Pentafluoride 25. CH2O - Formaldehyde 26. NH2Cl - Chloramine 27. CH4 - Methane 28. SO2 - Sulfur Dioxide 29. AlF3 - Aluminum Trifluoride 30. NH3 - Ammonia 31. SeH2 - Hydrogen Selenide 32. XeO3 - Xenon Trioxide 33. H2O - Water 34. CO2 - Carbon Dioxide 35. SCl2 - Sulfur Dichloride 36. NO2F - Nitryl Fluoride 37. CSe2 - Carbon Diselenide 38. IF5 - Iodine Pentafluoride 39. ClF3 - Chlorine Trifluoride 40. SF5Cl - Sulfur Pentafluoride Monochloride 41. PF3Cl2 - Phosphorus Trifluoride Dichloride 42. POCl3 - Phosphoryl Chloride 43. CCl4 - Carbon Tetrachloride 44. PF2Cl3 - Phosphorus Difluoride Trichloride 45. GeH4 - Germanium Tetrahydride 46. AlBr3 - Aluminum Tribromide 47. BeCl2 - Beryllium Dichloride 48. IBr3 - Iodine Tribromide 49. SO3 - Sulfur Trioxide 50. PCl3 - Phosphorus Trichloride 51. BeF2 - Beryllium Difluoride 52. BF3 - Boron Trifluoride