1. The Particle Model

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Why do we use Models?
Models are visual representations of abstract things. They are:
Simple to understand (simplified version of reality)
Explains several observations
Helps us predict future phenomena
Can be modified
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Particle Model
The Particle model is a scientific model based on the idea that matter is made up of tiny particles (ATOMS!!)
helps explain how particles behave and are organized in the three phases of matter.
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4. ***Important Facts***
Matter is not continuous but is made up of specific kinds of particles (extremely small)
Forces of attraction hold particles together (they attract to each other)
Particles are always moving
At high temperatures, particles move faster
(at low temperatures particles move slower)
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5. Phase Changes/States of matter
Matter can undergo many physical changes that change its appearance, but not its composition
E.g. Cut bread, spread butter on the bread, chew the bread (yum)
We will focus on:
Phase Changes/States of matter

6. Phases of Matter: Solids, Liquids & Gases
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Solids
Solids have definite structure and shape
Particles are very close together with strong forces of attraction
Very little freedom to move (can only vibrate in one spot)
**no container needed to hold their shape and volume **
**Particles are very organized**
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Liquids
Liquids have definite mass and volume, but not a definite shape (they take the shape of their containers)
Particles are close together but the bonds are weaker than solids (more freedom to move)
**more disorganized than solids)
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Gases
Gases have a definite mass but no definite volume or shape (they take the volume and shape of their containers)
Particles are far apart, and not bound by forces of attraction
**complete freedom of movement**
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Energy
In terms of energy:
Solids have the least energy
Liquids have medium energy
Gas has greatest energy
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14. Phase Changes p
A phase change is the transformation of matter from one state to another
May happen naturally (ice/snow melting)
Happens when a substance is heated or cooled

15. Phase Change
Are physical changes as the composition of the substance doesn’t change
Ex: Ice, water, and steam are still H2O molecules

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Phase Changes (p. 43)
Melting (solid to liquid) (Fusion)
Solidification (liquid to solid) (Freezing)
Condensation (gas to liquid)
Evaporation (liquid to gas) **Vaporization/Boiling**
Sublimation (solid to gas)
Deposition (gas to solid)
Ionization: (gas to plasma)
Recombination (plasma to gas)
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PHASE CHANGES
deposition
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PHASE DIAGRAM
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19. Particle Theory and phase changes
To change from a solid to a liquid a lot of energy is needed to break the bonds that hold the molecules in the solid form.
Similarly to go from liquid to gas, the molecules need more energy to break free of the surface of the liquid.
This change in state will produce a “plateau” in a heat curve
plateau

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21. Each pure substance passes from
Solid liquid gas
at precise temperatures (Physical Characteristic property)

22. Physical Characteristic Properties
Phase changes happen because of a substance’s specific physical characteristic properties:
Boiling Point: the temperature at which a substance turns from liquid to gas. The opposite of this is called condensation point.
Melting point: the temperature at which a substance goes from solid to liquid. The opposite of this is called freezing point (solidification).
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23. Pressure and Boiling or Melting Point
Water boils at lower temperatures at the top of a mountain. This is because there is less air pressure (air is thinner!)
There is less air pressing down on liquid water, so less heat energy is needed to get molecules to jump out of the liquid and become gaseous.
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