1. Polarity and Intermolecular Forces of Attraction

2. Covalent bonds mean sharing electrons between atoms…but it isn’t always FAIR/equal.
Fluorine LOVES TO GRAB electrons
Hydrogen ends up with less electrons

3. This ability to attract electrons to itself is called ELECTRONEGATIVITY
Electronegativity is the ability of an element to attract bonding pair of electrons in a chemical bond.

4. The periodic table can help us see that going towards Fluorine means increasing electronegativity
A Pauling electronegativity value of 4.0 (Fluorine) is the highest. Francium (Fr) has the smallest value at 0.7.

5. The periodic table can help us see that going towards Fluorine means increasing electronegativity
A Pauling electronegativity value of 4.0 (Fluorine) is the highest. Francium (Fr) has the smallest value at 0.7.

6. When a bond is POLAR this means we have a partial (+)/electron-poor and a partial (-)/electron-rich area.

7. Polar Bonds and Lone Pairs contribute to polarity but we need to see if they add or cancel each other.
AXE notation?
AX4 = tetrahedral
CCl4 is not polar but CHCl3 is polar. Why?

8. Polar Bonds and Lone Pairs contribute to polarity but we need to see if they add or cancel each other.
AXE notation?
AX3 = trigonal planar
BF3 is nonpolar because all the polar bonds cancel each other out

9. Polar Bonds and Lone Pairs contribute to polarity but we need to see if they add or cancel each other.
AXE notation?
AX2 = linear

10. Polar Bonds and Lone Pairs contribute to polarity but we need to see if they add or cancel each other.
Water is AX2E2, it is polar since both the contributions of the O-H bonds and the lone pairs do not cancel out.

11. Exercise: 1. Draw the proper Lewis Structure of. a. SOCl2. b. H2S. c
Exercise: 1. Draw the proper Lewis Structure of a. SOCl2 b. H2S c. HCN 2. Give AXE notation for geometry and identify the shape 3. Show polarities of bonds 4. Determine if the molecule is polar OVERALL or not.
Electronegativity Values:
S = O= 3.5
Cl = H= 2.1
C = (4.0 = most EN)

12. Know that we know if our molecules are polar or not, we can know a lot more on how substances behave!

13. On the basis of attraction of opposite charges, we can list down ways molecules can interact:
These are called “intermolecular forces of attraction” or IMFAs 

14. Ion-dipole interactions: a permanently charged ion attracts a polar molecule (called a dipole since it has both +/- ends, di- means two, so two-poled)
Which end of water is attracted to CATIONS? To ANIONS?

15. Ion-dipole interactions
Which end of water is attracted to CATIONS? To ANIONS?

16. Dipole-dipole, or simply called polar interactions are the next strongest…

17. Dipole-dipole, or simply called polar interactions are the next strongest…
The next slide shows you fragrance molecules, the structure of an alcohol (ethyl alcohol aka Ethanol),
Perfumes are often oils and esters (as shown in the next slide) dissolved in alcohol.
Beer has sugar

18. Dipole-dipole, or simply called polar interactions are the next strongest…
Sucrose (table sugar)
ethanol

19. A special strong version of a dipole-dipole interaction is called HYDROGEN BONDING
H-bonding occurs between an H (which is made electron-poor because it is bonded to F/O/N) and an electron-rich F/O/N atom. This is a very strong IMFA, stronger than normal Dipole-dipole interactions. This is why water, despite being so small a molecule, is a very very complex and mighty molecule. Water has such an amazing network of 3D hydrogen bonds

20. A special strong version of a dipole-dipole interaction is called HYDROGEN BONDING
H-bonding occurs between an H (which is made electron-poor because it is bonded to F/O/N) and an electron-rich F/O/N atom. This is a very strong IMFA. This is why water, despite being so small a molecule, is a very very complex and mighty molecule. Water has such an amazing network of 3D hydrogen bonds

21. Hydrogen bonding is ESSENTIAL TO LIFE… keeping our proteins, cells, tissues, organs all structured and functioning.

22. The next interactions, slightly weaker are the ions or dipoles with INDUCED DIPOLES
INDUCED DIPOLES – a non-polar molecule that has its electrons slightly affected by polarity of another polar molecule (dipole)
It’s like you have a metal object become magnetic too when you put a magnet against it.

23. The weakest intermolecular force of attraction is called DISPERSION FORCES
Think of it as induced-dipole induced- dipole.
Molecules have electrons around them, but in blobs that can change. They aren’t orbiting the nucleus in fixed orbits.
If the electron cloud/blob changes shape a bit, it becomes slightly polar.

24. Dispersion forces or non-polar interactions ARE VERY IMPORTANT AS WELL
Dispersion forces or non-polar interactions ARE VERY IMPORTANT AS WELL. They can be seen as negative polar-polar interactions.

25. Dispersion forces, are vital in so many ways…

26. All these IMFAs (intermolecular forces of attraction) explain so many things around us!
SOLUBILITIES…

27. Why isn’t caffeine very soluble in water?
Although caffeine has a lot of polar bonds, they seem to cancel each other out more or less making it not a very polar molecule.

28. MELTING POINTS/ BOILING POINTS
All these IMFAs (intermolecular forces of attraction) explain so many things around us!
MELTING POINTS/ BOILING POINTS
Explain why acetone boils/evaporates more easily than water even though it is a heavier/bigger molecule.
Acetone can only have dipole-dipole interactions. Water however has the stronger H-bonding type of dipole interactions. Even though water is a smaller molecule, the stronger attraction it has with the other water molecules make it more difficult for it to become a vapor (gas) where molecules are flying around solo.
ACETONE: 56°C
WATER: 100°C

29. All these IMFAs (intermolecular forces of attraction) explain so many things around us!
MELTING POINTS/ BOILING POINTS: Both use weak dispersion forces but why do they still differ in boiling points?

30. Soaps use 2 different IMFA’s: Ion-dipole interactions and NON-POLAR/Dispersion forces
ION-LIKE HEAD. With a negative charge RED = Oxygens
A detergent/soap molecule has 2 ends: an ionic/polar head that attracts water
And a non-polar tail that attracts oil and dirt.
NON-POLAR TAIL..
Black = Carbon
White = hydrogen

31. The polar/ionic head of soap is called HYDROPHILIC (water-loving) and the nonpolar tail is called HYDROPHOBIC (water-fearing)
A detergent/soap molecule has 2 ends: an ionic/polar head that attracts water
And a non-polar tail that attracts oil and dirt.
When the dirt binds to the tail of the molecule (yellow lines) it does so via dispersion forces / non-polar interactions.
The water then attracts the ionic/polar head and washes the soap-dirt partnered molecules away.

32. Superhydrophobic surfaces use nano-structures on their surfaces to create the lotus-leaf effect.
Liquids will prefer their own IMFAs over bonding to the small, rough surfaces breaking up their own bonds (like H-bonding for water)