2. Covalent vs. Ionic Bonds

3. How does your sense of smell work?

4. If a molecule fits into a receptor site in your nose, should all things smell? Why do you think you don’t smell the molecules of O2 , N2, or CO2 in the air?

5. Why do some molecules smell while others do not?

6. Objectives: What are intramolecular forces?
What are intermolecular forces?
What is the difference between a polar and a nonpolar molecule?
What is a partial charge?
What is a dipole?
What causes polarity?
What is electronegativity?
How can you predict the general direction of a dipole for any two atoms, using the periodic table?

7. Demonstration: Make the following table in your notes.
Compound
Observations
Effect of Charged Wand
Compound is Polar or Nonpolar?
Water
Isopropanol
Hexane

8. Charged Wand Demonstration

9. The charged wand experiment provides evidence that some molecules are attracted to a charge.
Polar molecules: molecules that are attracted to a charge because they have partial charges on them.
Nonpolar molecules: molecules that are not attracted to a charge.

10. One end of a polar molecule has a partial negative charge, and the other end of the molecule has a partial positive charge.
The individual molecules in polar liquids will respond when another charged substance comes near.

11. The partial charges on polar molecules cause individual molecules to be attracted to each other. Areas with a partial charge are called dipoles.

12. Intramolecular forces: forces that bond atoms together within one molecule
Intermolecular forces: the forces of attraction that occur between molecules

13. All molecules interact with each other, but the attractions between polar molecules tend to be stronger than those between nonpolar molecules.

14. In terms of polarity, why do you sense the smell of some things, but not others?
Receptors in your nasal cavity are polar.
Polar molecules are are attracted to a charge.
Polar molecules are attracted to each other.
Nonpolar substances will not be attracted to your polar receptors.

15. What makes a molecules polar?
If a penguin represents a hydrogen atom and the polar bear represents a chlorine atom, what does the ice cream cone represent in the image?
If neither of them lets go of the cone, who do you think would be able to pull it all the way towards itself?

16. Electronegativity: the tendency of an atom to attract shared electrons.
Why is water so polar?

17. What makes a molecule polar?
Polarity in a molecule is cause by unequal sharing of electrons between atoms.
Electronegativity is the tendency of an atom to attract shared electrons (pull electrons towards itself).
Anytime two atoms with different electronegativity values share electrons, there will be a partial negative charge on one atom and a partial positive charge on the other atom. These partial charges are called dipoles.

18. How can electronegativity be used to predict polarity and compare bond types?

19. Chemists have assigned an electronegativity value number to each atom.
This number represents the tendency of an atom to attract bonding electrons.
By using these numbers it is possible to compare the predict what type of bond two atoms will make (ionic, polar covalent, nonpolar covalent).
Why do Noble Gases NOT have electronegativity values?

20. Bond types are easiest to predict when you are dealing with two atoms.
Diatomic molecules: molecules with two atoms

21. How to predict whether bond type based on differences in electronegativity values?

22. How to determine bond type using electronegativity values?
1) Determine electronegativity values using periodic table.
2) Take the difference between your two values.
3) Use the “Difference in Electronegativity Scale” to determine bond type

23. Polarity is also dependent on the shape of a molecule.

25. What is a mole?
What is molar mass?
If you have one gram of glucose sugar ( g/mol) and one gram of salt (58.44g/mol), which is closer to a mole of itself?