1. Kinetic Molecular Theory
Section 12.1

2. V. Bond Type
All ionic compounds are solids at room temperature. Why?
Oppositely charged ions have strong attractive forces.

3. So, wouldn’t covalent bonds be strong and result in liquids or solids
So, wouldn’t covalent bonds be strong and result in liquids or solids? They share electrons.
NO. Molecules are usually gases.
The bonds themselves are strong (ie the bond between C and O in CO).
This is intramolecular forces. BUT. . .

4. The forces between neighboring CO molecules is weak .
This is intermolecular forces.

5. Intramolecular Force - +
C O - +
O C
Intermolecular Force

6. VI. Intermolecular Forces
Forces that exist between molecules
The physical state of a substance depends largely on the balance between the kinetic energies of the particles and the intermolecular attractive forces between particles.

7. Also, in general the greater the intermolecular forces, the higher the melting points of solids and the higher the boiling points of liquids.
Also larger constants such as heat of vaporization, heat of fusion, etc.

8. VI. Intermolecular Forces
A. London Dispersion Forces
B. Dipole-Dipole Forces
C. Hydrogen Bonding

9. VI. Intermolecular Forces
A. London Dispersion Forces
Present in all molecules
These are the only forces present in non-polar molecules (H2, N2) or noble gases (Ne, He)
They are a result of an induced dipole (board explanation)

10. A. Dispersion Forces (cont)
Larger molecules have a larger dispersion force.
Because the electron cloud can be more easily distorted, this causes an induced dipole
Larger atoms have larger e-clouds; larger clouds are more “polarizable” resulting in stronger London Forces

11. A. Dispersion Forces (cont)
Trend: moving down a group, atomic radii increases.
This results in a higher freezing point
A stronger dispersion force results in a higher boiling point for these molecules

12. B. Dipole-Dipole Forces
Forces present in polar molecules
The positive end of a polar molecule is attracted to the negative end of a neighboring molecule (see the CO explanation).

13. As a result, these molecules boil at higher temperatures because these are stronger forces than dispersion forces.
This explains why SO2 boils at a higher temperature than the non-polar CO2

14. C. Hydrogen Bonding
Some molecules have a higher boiling point than would be expected due to dispersion or dipole-dipole forces
When H bonds with F, O, or N the molecule boils at an unusually high temperature (H2O for example)

15. H-bonding is very strong. Why?
F, O, N are very electronegative
When H bonds with them, the result is a molecule that is almost like an ionic bond
There is a more definite + and - end, resulting in a very strong attraction between neighboring molecules

16. H-bonding is very strong. Why?
The bond is also strong because the small size of the elements involved; this allows the dipoles to come closer together, strengthening the bond

17. Mole Fraction
xA = moles of A
total moles

18. Mass Percent
Mass Percent = mass of solute
mass of solution
X 100%

19. Molality, m
molality = moles of solute
mass of solvent (kg)

20. Example
A solution was prepared by dissolving 17.1 g of sucrose C12H22O11 in 125 g of water. Find the molal concentration of this solution.

21. What First? 17.1 g C12H22O11 1 mol C12H22O11 342.34 g C12H22O11

22. Next
Convert water to kg
125 g water
0.125 kg water

23. Last
.0500 mol C12H22O11
0.125 kg H2O
= .400 m C12H22O11

24. Example 2
A solution of I2, in CCl4, is used when I2 is needed for certain chemical tests. How many grams of iodine must be added to prepare a m solution of I2 in CCl4 if g of CCl4 is used?

25. What First?
Change g CCl4 to kg
0.100 kg CCl4

26. Use the Equation
0.480 mol I2 = (X) mol I2
1 kg kg

27. Last
mol I g I2
1 mol I2

28. Answer
12.2 g I2

29. Example Problem
Look at Sample Exercise 11.2 on page 517