1. Condensed States of Matter
Chapter 14
Condensed States of Matter

2. I. States of Matter Three common states Solid Gas Liquid
Changes to solid if temp lowered below freezing point
Changes to gas if temp is raised about boiling point
These changes are called phase changes
During this process, the substance is not chemically changed, it is physically changed

3. A. Kinetic Molecular Theory: Liquids and Solids
Kinetic molecular theory of gases used assumptions that simplified and allowed us to predict behavior
Particles of an ideal gas are in constant, random, straight-line motion
Collisions between gas particles are perfectly elastic
Average kinetic energy of gas particles depends upon temperature
Gas particles exert no attractive or repulsive forces on one another

4. Why do these assumptions work?
Gas particles are relatively far apart (as compared to particles of a liquid or solid)
Since they are so far apart, the forces of attraction are very weak
At moderate temperatures and pressures, the attraction can be ignored
These assumptions do not work for liquids and solids because the particles are closer together

5. Intermolecular Forces
Covalent bonds are the force that holds individual atoms of a molecule together
So, what holds one molecule close to another in a liquid or solid?
Intermolecular forces: forces of attraction between two or more molecules
Which state of matter has the weakest intermolecular forces?
Gases
Why?

6. Effect of Temperature
Average kinetic energy of a gas increases with temperature
At higher temperatures, if two particles get close enough to be attracted, the average kinetic energy is great enough to overcome this attraction
At lower temperatures, the average kinetic energy is lower, and therefore the attraction cannot be overcome and the particles cannot break away from each other
They group together and form a liquid
This process is known as condensation
As intermolecular forces increase, condensation occurs at higher temperatures

7. Effect of Pressure
Increasing pressure forces gas particles closer together
The closer they are, the stronger the intermolecular forces
If pressure is increased enough, particles are close enough together to condense and form a liquid

8. B. Types of Intermolecular Forces
Van der Waals Forces: The attractions between neutral particles
London dispersion forces
Occur between nonpolar molecules
Due to instantaneous dipoles (temporary) which arises from random movements of electrons
This can cause an induced dipole in another molecule
A second atom or molecule, in turn, can be distorted by the appearance of the dipole in the first atom or molecule (because electrons repel one another) which leads to an electrostatic attraction between the two atoms or molecules.
Because of the constant motion of the electrons, an atom or molecule can develop a temporary (instantaneous) dipole when its electrons are distributed unsymmetrically about the nucleus

9. Dipole- dipole forces Occur between (neutral) polar molecules
Electrostatic connection between positive end of one dipole and the negative end of an adjacent dipole

10. Hydrogen bonding
Dipole-dipole interactions that involve a hydrogen atom in a polar bond (F, O, & N)

11. Ion-Dipole Forces: The attraction between an ion and the charged end of a polar molecule
Common in solutions containing soluble ionic salts

12. II. Change of State A. Phase Changes Evaporation: liquid to vapor
Rate is dependent upon temperature
At any given temperature, the rate is constant
More and more particle enter the vapor phase
This increases the number of gas particles hitting the liquid surface and some particles condense
So as the number of gas particles increases (over time), the rate of condensation increases
Eventually, rate of vaporization and rate of condensation become equal
Explain the demonstration in terms of relative strength of intermolecular forces
draw diagram showing bell-shaped curves for lower and higher temperature and highest three % with energy > E(min)
Draw diagram showing rate vs time w/ rate of caporization and rate of condensation

13. Vapor Pressure: partial pressure of the vapor above a liquid
Since partial pressure of a gas increases as number of gas particles increases, evaporation increases the vapor pressure
At each temperature, vapor pressure is constant (since rate of evaporation is constant)
So, as temperature increases, vapor pressure increases due to increased evaporation
Is related to strength of intermolecular forces
Stronger forces equal lower vapor pressure
Molecules that readily evaporate (due to weak IM forces) are referred to as being volatile

14. Boiling point: temperature at which the vapor pressure equals the external pressure acting on a liquid
How was this definition arrived at?
At sea level (where atmospheric pressure is 1 atm), water boils at 100°C
In Denver (where altitude is 1600 m and atmospheric pressure is 0.83 atm), water boils at 95°C
The increased pressure at sea level compresses the particles, increasing the intermolecular forces
This means it takes more energy (or higher temperature) to break apart those forces
Explain the demonstration in terms of external pressure and intermolecular forces

15. Freezing point Sublimation Change from liquid to solid
Reverse process is called melting or fusion
The stronger the intermolecular forces, the higher the melting point
Sublimation
Change from solid directly to gas
Reverse process is called deposition

16. B. Heating Curves Temperature v Time graph Heat of fusion
Energy it takes to melt a substance
Molar heat of fusion
Energy required to change 1 mole of ice into 1 mole of water at 0°C
Heat of vaporization
Energy to boil a substance
Molar heat of vaporization
Energy required to change 1 mole of water into 1 mole of water vapor
-Draw example heating curve

17. III. Structure and Properties of Liquids
A. Surface Tension
When the surface of a liquid acts like a weak, elastic skin
The attractive force that occur between molecules in a single (same) substance is called cohesion
This force pulls equally in each direction on individual particles (and therefore no net force) in the interior of a liquid
On the surface, however, particles are attracted to the interior so there is a net inward pull

18. Strength is related to the strength of intermolecular forces
The stronger the intermolecular forces, the greater the cohesion, thus the greater the surface tension
Prevents water from being a good wetting agent
Force of attraction between two different substances is called adhesion
“wetting ability” depends on relative strength of cohesion and adhesion
Explain why the addition of soap caused the needle to sink in the demonstration

19. B. Water: A Unique Liquid
Densities of water and ice
Hydrogen bonding occurs in the solid and liquid phases of water
When water freezes, the hydrogen bonds define the three-dimensional shape of the crystal
In this case, the molecules are held farther apart in the solid phase
This results in ice being less dense than liquid water, so ice floats
Explain how this property (expansion in solid form) is beneficial to plant and animal life in lakes.

20. Water’s heat capacity
Heat capacity: the thermal energy required to raise the temperature of one kilogram of a substance by one degree Kelvin
Water has much higher heat capacity compared to other liquids due to strong hydrogen bonding
While other liquids also have hydrogen bonding, the HB in water is 3-Dimensional due to two unbonded pairs of electrons on each oxygen

21. IV. Structure and Properties of Solids
Solids are classified as either crystalline or amorphous (without shape)
A. Metallic and Covalent Solids
Metallic solids
Unit cell: the smallest unit from which the larger crystal can be built (i.e. the repeating pattern in smallest form)
Seven different types found in all crystalline solids; four of them in metallic solids
Three are cube-shaped; one is hexagonal
Held together by nondirectional metallic bonds
Covalent network solids
Held together by extensive network of directional covalent bonds
-possibly build a model of each type of crystal structure using kits

22. B. Molecular and Ionic Solids
Molecular solids
Molecules held in place by relatively weak intermolecular forces
Ionic Solids
Three-dimensional arrangements of positive and negative ions
Held together by electrostatic attractions
Arrangement depends on:
Sizes of ions
Ratio of cations to anions