STATES OF MATTER:  Solids, Liquids, Gases, and Plasma


Kinetic Theory – all matter is made up of small particles (molecules) that are in constant motion. The higher the temperature is, the more the molecules move around. When the temperature is lowered, the molecules move around more slowly.


There are four states of matter: solid, liquid, gas, and plasma.


Solids – solids have a definite volume and a definite shape. The molecules that make up a solid are packed together tightly and have very little movement.


Liquids – liquids have a definite volume and no definite shape (a liquid will take on the shape of whatever container they are in). The molecules that make up a liquid are able to move more freely than those of a solid. Because of this, they are able to slide right past one another (this is why liquids SPILL!)


Gases – gases have no definite volume and no definite shape. Gas molecules are fast and free moving. Gases will spread out to fill up whatever space they are given, like when perfume is spilled in a room. This spreading of a gas is called diffusion.


Plasma – plasma is the most common state of matter in the universe. It has no definite volume, no definite shape, and is composed of electrically charged particles with large amounts of energy. Plasma is found in the sun and other stars, lightning bolts, neon and fluorescent lights, and fire.



When energy is added or taken away from matter, it can change from one phase to another. Phase changes are boiling, melting, freezing, vaporizing, condensing, evaporating, and sublimation.

Fill in the blanks below with the correct phase change.


  1. ____________________________  is when a solid becomes a liquid


  1. ____________________________  is when a liquid becomes a gas. This phase change includes both ________________________  and  ___________________________*****


  1. ___________________________  is when a gas becomes a liquid


  1. ___________________________  is when a liquid  becomes a solid


  1. ___________________________  is when a solid changes directly into a gas without going through the liquid phase.


****vaporization is a change from liquid to a gas. There are two kinds of vaporization:

1)      evaporation – vaporization that occurs at the surface of a liquid. It is usually a slow process that can occur at just about any temperature

2)      boiling – vaporization that occurs throughout a liquid. It occurs at a specific temperature and pressure.

Water boils at 100 degrees C at sea level…what about 8000 feet above sea level?


What about the boiling point of water in the bottom of the Grand Canyon?




  1. Why can you see your breath on a cold day?



  1. Why does a cold soda can “sweat” on a hot and humid day?



  1. What are melting and freezing “points” ?



    Phase Change Diagram – You will receive a worksheet after we finish these notes. Be sure to look over the phase change diagram on the worksheet!!!


Question: What happens to the temperature during the phase change? What about the energy during a phase change??


Remember: during the actual phase change (such as boiling, melting, freezing, condensing), the temperature stays the same (constant) while the amount of heat energy changes!!!



Thermal Expansion

We already said that molecules move around more with the addition of heat energy. They also tend to spread apart. This is known as THERMAL EXPANSION.

Definition: thermal expansion is an increase in size of a substance when temperature is increased (and the decrease in size when temperature is decreased).


Why is there space between the slabs of concrete on roads and sidewalks?



How and why does a hot air balloon work?



How and why does a thermometer work?



Can you name a substance that does NOT follow the thermal expansion definition? (a substance that expands when it freezes???