The Particle Model

Template copyright 2005 www.brainybetty.com 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 2/23/2019 Template copyright 2005 www.brainybetty.com

Template copyright 2005 www.brainybetty.com 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. 2/23/2019 Template copyright 2005 www.brainybetty.com

***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) 2/23/2019 Template copyright 2005 www.brainybetty.com

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

Phases of Matter: Solids, Liquids & Gases 2/23/2019 Template copyright 2005 www.brainybetty.com

Template copyright 2005 www.brainybetty.com 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** 2/23/2019 Template copyright 2005 www.brainybetty.com

Template copyright 2005 www.brainybetty.com 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) 2/23/2019 Template copyright 2005 www.brainybetty.com

Template copyright 2005 www.brainybetty.com 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** 2/23/2019 Template copyright 2005 www.brainybetty.com

Template copyright 2005 www.brainybetty.com Energy In terms of energy: Solids have the least energy Liquids have medium energy Gas has greatest energy 2/23/2019 Template copyright 2005 www.brainybetty.com

Phase Changes p. 43-45 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

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

Template copyright 2005 www.brainybetty.com 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) 2/23/2019 Template copyright 2005 www.brainybetty.com

Template copyright 2005 www.brainybetty.com PHASE CHANGES deposition 2/23/2019 Template copyright 2005 www.brainybetty.com

Template copyright 2005 www.brainybetty.com PHASE DIAGRAM 2/23/2019 Template copyright 2005 www.brainybetty.com

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

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). 2/23/2019 Template copyright 2005 www.brainybetty.com

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. 2/23/2019 Template copyright 2005 www.brainybetty.com