physical science

1. PHYSICAL
SCIENCE
ROWENA M. FLORES
SUBJECT TEACHER

2. Different properties dependent on intermolecular forces.
Phase at room temperature
When molecules have strong intermolecular forces of attraction, they
are packed close together. They often exist as condensed phase (solid
or liquid) at room temperature.
When molecules have weak intermolecular forces of attraction, they
are far apart from each other. They often exist as gas at room
temperature.

3. Solubility
Solubility refers to the ability of a substance to dissolve in a
given amount of solvent at a specified temperature.
Recall the rule “like dissolves like.” When the solute and the
solvent both exhibit the same intermolecular forces of
attraction, they form a solution.

4. Melting point and Boiling point
If molecules stick together more, they'll be tougher
to break apart
Stronger intermolecular forces → higher melting
and boiling points

5. Surface Tension
Surface tension is a measure of the toughness of
the surface of a liquid
Stronger intermolecular forces → higher surface
tension.

6. Viscosity
Viscosity is a measure of how well substances flow.
Stronger intermolecular forces → higher viscosity.

7. The properties of molecules depend on the type
and strength of their intermolecular forces of
attraction.
Phase at room temperature
When molecules have strong intermolecular forces of
attraction, they are packed close together. They often exist
as condensed phase (solid or liquid) at room temperature.
When molecules have weak intermolecular forces of
attraction, they are far apart from each other. They often
exist as gas at room temperature.

8. Solubility
Solubility refers to the ability of a substance to
dissolve in a given amount of solvent at a specified
temperature.
Recall the rule “like dissolves like.” When the solute
and the solvent both exhibit the same intermolecular
forces of attraction, they form a solution.

9. Melting point and Boiling point
If molecules stick together more, they'll be tougher
to break apart
Stronger intermolecular forces → higher melting
and boiling points

10. Surface Tension
Surface tension is a measure of the toughness of
the surface of a liquid
Stronger intermolecular forces → higher surface
tension.

11. Viscosity
Viscosity is a measure of how well substances flow.
Stronger intermolecular forces → higher viscosity.

12. Vapor pressure
This is a small amount of gas that is found
above all liquids.
Stronger intermolecular forces → Lower vapour
pressure.

13. Activity:
 1. List the following molecules in order of increasing
surface tension: C3H8, CH4, CH3COOH, C2H6
 2. List the following molecules in order of increasing
boiling point: Br2, F2, I2, Cl2,
 3. Which has the higher vapour pressure, C20H42 or
C30H62?

14. LET’S ANSWER
 1. List the following molecules in order of increasing surface
tension: C3H8, CH4, CH3COOH, C2H6
Answer:
Higher surface tension corresponds to stronger intermolecular forces.
1. CH3COOH has the ability to hydrogen-bond. It will probably have the
strongest intermolecular forces.
 2. CH3COOH is the only one of these molecules to have a dipole, and we
already decided it has the strongest intermolecular forces.

15.  3. Of the molecules that are left, the largest one (C3H8) likely has
the strongest London dispersion forces. The smallest (CH4) likely
has the weakest intermolecular forces.
 The answer is: CH4, C2H6, C3H8, CH3COOH
 2. List the following molecules in order of increasing boiling point:
Br2, F2, I2, Cl2,
Higher boiling points will correspond to stronger intermolecular
forces.

16.  1. None of these have hydrogen bonding.
 2.None of these have dipoles.
 3. Bigger molecules will have stronger London dispersion
forces. So I2 has the strongest forces, and F2 will have
the weakest. Correspondingly, I2 will have the highest
boiling point and F2 will have the lowest boiling point.
 Answer: F2, Cl2, Br2, I2

17. 3. Which has the higher vapour pressure, C20H42 or
C30H62?
Answer
Higher vapour pressures correspond to weaker
intermolecular forces.
1. None of these have hydrogen bonding.

18.  2. None of these have dipoles.
 3. Bigger molecules will have stronger London
dispersion forces. So, C30H62 has the stronger
intermolecular forces and C20H42 has the weaker
intermolecular forces.
 Answer: C20H42 has the higher vapour pressure, since
the molecules stick together less

19. ASSIGNMENT:
Explain how intermolecular forces affect the
properties of the following substances.
1. Which has higher boiling point, H2O or H2S?
2.Which is most likely solid, F2 or I2?