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Phases of Matter. Chapter 10. Phases of Matter: are determined by the energy content and movement of the particles. What keeps the particles in liquids and solids together?. The movement of particles is directly related to the temperature of the substance,

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what keeps the particles in liquids and solids together
What keeps the particles in liquids and solids together?

The movement of particles is directly related to the temperature of the substance,

as the temperature cools the movement of the molecules slows and the molecules

maybe attracted to each other.

This is referred to as INTERMOLECULAR FORCES. Intermolecular forces are the

attraction between molecules. These attractions are weaker than intramolecular

forces like ionic and covalent bonds.

The intermolecular forces can determine many of the physical properties of the

substance. The stronger the intermolecular forces the higher the melting and

boiling points of the substance. Why do you think this might be?

slide4
Why?

The stronger the intermolecular forces the higher the energy required to disturb or break the attractions.

types of intermolecular forces
Types of intermolecular forces:

Dispersion Forces (Van der Waals):

Temporary attraction created as electrons orbit

the nucleus.

(-)

(-)

+ +

Positive nuclei will repel each other.

types of intermolecular forces6

Dispersion Forces (Van der Waals):

Temporary attraction created as electrons orbit

the nucleus.

(-)

+ (-) +

When the electrons are concentrated on the same side as an exposed

positive nuclei there will be an attraction. Creating a temporary bond between

the two atoms.

Types of intermolecular forces:
types of intermolecular forces7

(-)

+ (-) +

H

H

δ+

δ+

δ-

δ-

H

H

N

N

H

H

H

H

O

O

H

H

Types of intermolecular forces:

Dispersion Forces (Van der Waals):

Temporary attraction created as electrons orbit

the nucleus. (weak attraction)

Dipole – Dipole:

The attraction between the oppositely charged ends of polar molecules.

Hydrogen Bonding:

The attraction created when a hydrogen atom is bonded to a highly

Elecronegative atom (F, O, N). This attraction causes a higher than

expected boiling point. (strong attraction)

how do substances change state

Beginning State

Ending State

Process of Change

How do substances change state?

Solid

Liquid

Melting

Solid

Gas

Subliming

Liquid

Solid

Freezing

Liquid

Gas

Evaporating/Boiling

Gas

Solid

Deposition

Gas

Liquid

Condensing

boiling points

Location

Altitude (ft)

Pressure

Boiling Point

Boiling Points
  • The temperature at which a substance turns from liquid to vapor
  • Thought question:
  • Is the boiling point of a liquid the same in every location?

NO!

Boiling point is directly related to atmospheric pressure, and indirectly related to altitude!

Sea Level

0

760 mmHg

100 ºC (373 K)

Mt. Everest

29,028

240 mmHg

70 ºC (343 K)

boiling vs evaporation
Boiling vs. Evaporation

Evaporation

Occurs below the boiling point, only at the surface of the liquid.

Occurs at the boiling point, throughout the entire liquid.

Boiling

Normal Boiling Point: the temperature at which vapor pressure of a liquid is equal to atmospheric pressure.

Heat of vaporization: the amount of heat required to vaporize a liquid.

freezing and melting points
Freezing and Melting Points

At what temperature does water freeze?

SAME!

0 ºC

(Freezing point)

At what temperature does ice melt?

0 ºC

(Melting point)

Heat of Fusion: the amount of heat required to melt a solid to liquid

slide12

We often use graphs to show the correlation between vapor pressure and boiling. The graph below is the vapor pressure curve for four different substances. Using this graph we can find the “Normal boiling point” for any substance by observing its boiling point at standard pressure (101.3 kPa, 1 atm, 760 mmHg).

For example the “normal boiling point” of substance A would be 35°C. What would the normal boiling of substance D be?

100°C

Based on this information, what do you think substance D might be?

Water

slide13

Line D represents water. If the atmospheric pressure in a flask is lowered to 70 kPa, water would boil at what temperature?

slide14

Line D represents water. If the atmospheric pressure in a flask is lowered to 70 kPa, water would boil at what temperature?

92ºC

do the practice graph in your packet
Do the practice graph in your packet.
  • Answers:
  • 1. ~32kPa, ~7kPa (your answer may differ by +/- 1)
  • 2. 70ºC
  • 3. ~21kPa
  • 4. ~74ºC, ~115ºC
particles are always in motion
Particles are Always in Motion

Kinetic-Molecular Theory

GASES

  • Gases are composed of tiny particles
  • Particles are in constant motion
  • Elastic collisions occur between particles
  • There are no attractive forces between particles
  • Kinetic Energy increases when temperature increases.

Ideal Gases!

particles are always in motion17
Particles are Always in Motion

Kinetic-Molecular Theory

LIQUIDS

  • Viscosity: the friction or resistance to motion that exists between the molecules of a liquid
  • Surface Tension: the imbalance of forces at the surface of a liquid
particles are always in motion18
Particles are Always in Motion

Kinetic-Molecular Theory

SOLIDS

  • Particles are “locked” in position and can only vibrate
  • Can be classified by three main characteristics:
    • Hardness
    • Electrical Conductivity
    • Melting Point
how do we classify solids
How do we classify solids?
  • Crystalline Solids:
    • organized, repetitive unit cells, sharp melting point
    • metallic: conduct electricity well
    • molecular: soft, low melting point
    • ionic: hard, brittle
    • covalent-network: conduct electricity at high temperatures
  • Amorphous Solids:
    • not “true” solids because molecules do move some
    • high viscosities make them appear solid
    • they soften before melting
for next class
For Next Class:
  • Complete homework page of packet.