STATES OF MATTER:

Matter exists in three common states: ___________________________, Liquid, and ___________________________

A liquid will change its state to become a solid if its temperature is lowered below its ___________________________ point.

Also, a liquid will change its state to become a gas if its temperature is raised above its ___________________________ point.

PHASE CHANGES:

A phase change is when a substance changes from one state (Gas, Liquid, Solid) to another state.

The particles which make up the substance DO NOT change chemically.

A phase change is a ___________________________ change.

KINETIC MOLECULAR THEORY: LIQUIDS and SOLIDS

The forces between Gas Particles are very ___________________________ (and often ignored).

Kinetic: Refers to Energy of Motion. Therefore, Kinetic Molecular Theory deals with the energy of the molecules in motion.

For Liquids and Solids, the attractive forces between particles must be considered because the particles are ___________________________ together.

Covalent Bonds: are the forces that hold atoms together within a molecule due to the sharing of electrons between the atoms.

Intermolecular Forces: The forces of ___________________________ between two or more molecules.

* Gases have the weakest intermolecular forces.

* Liquids have slightly stronger intermolecular forces than gases, but still weak enough to allow particles to move, or flow past one another.

-- The rate of flow depends on the shape of the molecule, temperature and pressure, and the strength of the intermolecular forces.

* Solids have a ___________________________ intermolecular forces than liquids. Therefore, molecules stay in a given position (but the molecules can vibrate - not a flowing action.)

EFFECT OF TEMPERATURE:

The average kinetic energy of a gas ___________________________ with an ___________________________ in temperature.

Condensation: The conversion of a gas to a ___________________________.

-- For gas particles, when the temperature lowers, the average kinetic energy is lower and the gas particles do not have enough energy to break away from each other, so they group together to form a liquid.

Condensation occurs when:

- The strength of the intermolecular forces are large, condensation will occur at higher temperatures.

- If the strength is small, condensation will occur at low temperatures.

For future reference, when we talk about pressure equaling One Atmosphere, One Atmosphere deals with the average air pressure, at sea level, here on Earth (1 atm = 101.3 kilopascals = 760 mm Hg.)

Increasing the Pressure causes the gas particles to move closer together. Therefore, the closer the particles - the ___________________________ the intermolecular forces.

If the intermolecular forces are strong enough (due to high pressure) a gas may change to a ___________________________ without lowering the temperature.

Conversely, if the intermolecular forces are weak enough (due to low pressure) a liquid may change to a ___________________________ without increasing the temperature.

-- An automobile's cooling system: the temperature of the water and coolant can reach temperatures close to 300⁰ F, the substance "should" be a gas near this temperature, but the pressure of the system is high and keeps the liquid from converting to a gas.

-- Liquid Air; CO₂ in cans, pressure inside the can is high enough to make the CO₂ a ___________________________ at room temperature.

TYPES OF INTERMOLECULAR FORCES:

- 3 Kinds of Intermolecular which hold molecules together.

1) Dispersion Forces

2) Dipole-Dipole Forces

3) ___________________________ Bonding

Collectively, these intermolecular forces are the Van Der Waals Forces.

DISPERSION FORCES:

Momentary dipoles may form in Nonpolar Molecules (this occurs because the electrons are always changing.)

Dispersion forces arise when the positive end of one momentary dipole is attracted to the negative end of another momentary dipole.

Dispersion forces are the ___________________________ intermolecular forces acting between Nonpolar Molecules.

The larger the molecular mass of a Nonpolar compound, the greater the dispersion forces and the greater the boiling point of the liquid.

Fluorine condenses at the frigid temperature of 85K (-188⁰C) because the average kinetic energy is sufficiently low to allow the dispersion forces to condense the gas into a liquid.

In noble gases, dispersion forces are the only forces of attraction acting between the same atoms.

DIPOLE - DIPOLE FORCES:

Dipole - Dipole forces arise from the ___________________________ attraction between the positive end of one dipole and the negative end of an adjacent dipole.

Dipole - Dipole forces exist only between ___________________________ MOLECULES.

Substances with Dipole - Dipole forces generally have Stronger Intermolecular Forces than those with dispersion forces (with the same mass.)

Dipole - Dipole interactions are only about 1/100th as strong as Ionic or Covalent Bonds (between atoms in the molecule).

HYDROGEN BONDING:

Hydrogen Bonding DOES NOT take place ___________________________ a molecule.

Hydrogen Bonding occurs between molecules.

In Hydrogen Bonding, electrons are NOT shared.

Hydrogen bonding occurs between molecules that have N ® H, O ® H, or F ® H Bonds.

Hydrogen bonding is about TEN times stronger than "ordinary" Dipole - Dipole Forces.

Hydrogen bonding between molecules is WEAKER than Covalent bonding (Within the molecule).

HOMEWORK QUESTIONS:

2a. Describe how two nonpolar molecules can attract one another.

2b. What are Dipole-Dipole forces? Explain how these forces arise between molecules.

2c. Explain what hydrogen bonding is, and under what conditions does hydrogen bonding occur?

2d. In pure samples of each of the following, indicate the kinds of intermolecular forces that can occur: Ne, I₂, NH₃, CO₂, CH₄, and CH₃OH.

CHANGES OF STATE:

- Average Kinetic Energy determines the ___________________________ of molecules.

PHASE CHANGES:

Vapor: Is the ___________________________ form of a substance that exists as a liquid or a solid under normal conditions of temperature and pressure.

Evaporation (or Vaporization): The change from a liquid to a ___________________________.

- For a liquid to evaporate, the particles must have enough energy to ___________________________ the intermolecular forces that hold the molecules together in the liquid phase.

Temperature effects the rate of evaporation.

However, in a closed system, as more and more particles go into the vapor phase, the number of gas particles hitting the surface of the liquid increases. After a period the rate of vaporization will equal the rate of condensation.

VAPOR PRESSURE:

The ___________________________ pressure of the vapor above a liquid is called the Vapor Pressure.

- The partial pressure of a gas depends on the ___________________________ of gas particles present.

** More gas particles: Higher vapor pressure

** When evaporation occurs - the vapor pressure above a liquid increases.

- Vapor pressure also depends upon the temperature.

** Temperature ___________________________ the rate of evaporation - therefore, increasing the vapor pressure.

Vapor pressure depends on the strength of the intermolecular forces between the particles of the liquid.

Stronger Intermolecular Forces = Lower Vapor Pressure

(Fewer particles will have enough kinetic energy to overcome the attractive forces.)

Liquids that readily evaporate at room temperature are classified as ___________________________.

As the atmospheric pressure increases; the temperature must be increased to achieve vaporization.

Also, as the pressure nears zero, the partial pressure increases, therefore, temperature can be much lower to achieve vaporization.

BOILING POINT:

Boiling Point is the temperature at which a substance changes from a liquid to a gas.

- As pressure increase the boiling point increases.

- As pressure lowers the boiling point decreases.

Normal Boiling Point: The boiling point for a substance at one atmosphere.

FREEZING POINT:

Freezing: Is the phase change at a constant temperature and pressure from liquid to solid.

Melting: Reverse process of Freezing at a constant temperature and pressure.

Freezing and Melting occur at the same temperature (for a given substance).

At this temperature, a substance can (does) exist as a solid and a liquid simultaneously until the phase change is complete.

- Pressure DOES NOT determine the rate of FREEZING.

SUBLIMATION:

Sublimation: The process by which a solid changes into a gas (without changing into a liquid first).

Deposition: The process by which a gas changes into a ___________________________.

HEATING CURVES: (PHASE CHANGE DIAGRAM)

A heating curve is a temperature - verses - time graph that is useful for illustrating the energy changes that takes place as a substance is heated.

Heat of Fusion: Heat required to weaken intermolecular forces to change a solid to a liquid.

Molar Heat of Fusion: The energy to change one mole of a solid into one mole of a liquid.

Heat of Vaporization: Heat required to weaken intermolecular forces to change a liquid to a gas.

HOMEWORK QUESTIONS:

3a. Acetone has greater vapor pressure than ethyl alcohol at 25⁰C. Predict which substance has stronger intermolecular forces. Explain your answer.

3b. The boiling point of ethyl alcohol is 78.5⁰C. Will the boiling point of acetone be lower or higher? Explain your answer.

3c. What happens to the temperature of ice at -10⁰C when it is heated?

3d. What happens to the temperature when liquid water at 100⁰C and 1 atm is heated?

3e. Compare the boiling point of water at 1 atm to the boiling point of water at 2 atm?

STRUCTURE and PROPERTIES OF LIQUIDS:

Surface Tension: Causes the surface of a liquid to act like a weak, elastic "skin".

___________________________ of the molecules is the cause for Surface Tension.

Strength of Surface Tension is related to the ___________________________ forces.

Stronger Intermolecular Forces = Greater Cohesion [ Therefore, Greater Surface Tension ]

Water has a "strong" surface tension compared to most liquids because of the Hydrogen Bonding between water molecules.

Surface Tension prevents water from being a "wetting" agent.

Water beads on wax, but adheres to dirt and salt (on dirty cars).

Adhesion: The force of attraction between ___________________________ substances.

Soap: Is used to make water a better wetting agent - soap ___________________________ the water's surface tension.

WATER: A UNIQUE LIQUID

Hydrogen bonds cause water to form a rigid structure which produces many "holes" in the solid.

Therefore, solid water is LESS DENSE than when it is a liquid.

When water freezes, it INCREASES in volume by about nine (9) percent.

Most substances that go from the liquid phase to the solid phase increase their density - Water does not.

In winter, when a lake freezes, ice floats on the surface. Therefore, insulating the warmer, denser water below the ice.

WATER'S HEAT CAPACITY:

Water absorbs much ___________________________ than most liquids for a given change in temperature.

Heat Capacity: Is the thermal energy required to raise the temperature of one kilogram of a substance by one kelvin.

Water has a higher heat capacity because of the ___________________________ bonds.

Water requires more energy to achieve a given temperature change because so much energy is used to overcome the Hydrogen bonding.

HOMEWORK QUESTIONS:

4a. Explain the surface tension of water on a molecular level.

4b. Why is the heat capacity of water so large? Explain your answer.

STRUCTURE and PROPERTIES OF SOLIDS:

Amorphous Solids: Without shape; solids which are not arranged in a regular pattern.

METALLIC and COVALENT SOLIDS:

Metallic Solids:

Unit Cell: Smallest block-like unit from which larger crystals can be built.

COVALENT NETWORK SOLIDS:

Covalent Network Solids are held together with an extensive network of covalent bonds. The entire network can be considered to be one giant molecule.

Covalent network solids can be two-dimensional and one-dimensional.

Example: Carbon: Graphite is a 2-D shape, Diamond is a 3-D shape.

Most covalent network solids have an ___________________________ melting points.

MOLECULAR and IONIC SOLIDS:

MOLECULAR SOLIDS:

Molecular Solids are held together by relatively weak intermolecular forces. Examples: Ice, Dry ice (water).

No covalent or ionic bonds need to be broken to melt a molecular solid, therefore, molecular solids have relatively low melting points.

Larger molecules will have a ___________________________ point than small molecules.

IONIC SOLIDS:

Ionic solids have a 3-D crystalline arrangements of positive and negative ions.

Ionic solids are held together by electrostatic attractions (strong)

Also, Ionic solids have ___________________________ points.

FACTORS THAT DETERMINE ARRANGEMENT OF MOLECULES:

- Size of the atoms will determine the ___________________________ of the unit cell.

- The ratio of Cations to Anions.

** Each ion is surrounded by ions of opposite charge.

** The charge and size affects the ___________________________ point.

HOMEWORK QUESTIONS:

5. What type of crystals do each of the following form?

a. ice (water) __________________________, b. iron __________________________, c. sodium chloride __________________________

5. Which type of forces are involved in the crystalline structure of each crystal in the above question:

d. ice (water) ____________________________________________________

e. iron ___________________________________________________

f. sodium chloride __________________________________________

5g. Explain why carbon dioxide is a gas at room temperature, whereas iodine is a solid.

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