Middle School Physical Science: States of Matter - Solids, Liquids, Gases, and Plasmas — Flashcards

Energy and States of Matter    
Why do different states of matter have different properties? It's because of differences in energy at the level of atoms and molecules, the tiny particles that make up matter. Energy is the ability to cause changes in matter. Energy that causes matter to move is called kinetic energy. According to the kinetic theory of matter, the particles that make up matter have kinetic energy and are constantly moving.    
So why don't all the particles move apart? Particles of matter of the same substance, such as the same element, are attracted to one another. This force of attraction tends to pull the particles closer together. The particles need a lot of kinetic energy to overcome the force of attraction and move apart. It's like a tug of war between opposing forces.    
The kinetic energy of individual particles is on one side, and the force of attraction between different particles is on the other side. The outcome of the “war” depends on the state of matter.    
 

- In solids, particles don't have enough kinetic energy to overcome the force of attraction between them. The particles are packed closely together and cannot move around. All they can do is wiggle, or vibrate, in place.    
This explains why solids have a fixed volume and a fixed shape.    
- In liquids, particles have enough kinetic energy to partly overcome the force of attraction between them. They can slide past one another but not pull apart. This explains why liquids can change shape but have a fixed volume.    
- In gases, particles have a lot of kinetic energy. They can completely overcome the force of attraction between them and move apart. This explains why gases have neither a fixed volume nor a fixed shape.