5. Kinetic Particle Theory

Arrangement of Particles

• Solid: Closely packed, regularly arranged
  
• Liquid: Slightly further apart, irregularly arranged
  
• Gas: Very far apart, irregularly arranged
  

Movement of Particles

• Solid: Vibrate and rotate about fixed positions
  
• Liquid:  Slide past each other within the liquid
  
• Gas: Moves freely & rapidly in all directions
  

Melting: Solid to Liquid

• As temperature increases, the particles in the solid gain kinetic energy & vibrate faster in their fixed positions.
  
• At the melting point (no further increase in temperature), some particles gain enough energy to overcome the forces of attraction which holds them in fixed positions and become further apart and are able to slide past each other.
  
• When all the particles have gained enough energy to overcome the forces of attraction, temperature starts to increase beyond melting point.
  

Boiling: Liquid to Gas

• As temperature increases, the particles in the liquid gain kinetic energy & move faster but are still closely packed together.
  
• At the boiling point (no further increase in temperature), some particles gain enough energy to overcome the forces of attraction and become very far apart and are able to move in all directions.
  
• When all the particles have gained enough energy to overcome the forces of attraction, temperature starts to increase beyond the boiling point.
  

Diffusion

• The movement of particles from a region of higher concentration to a region of lower concentration until both regions are of equal concentration.
• Diffusion occurs fastest in a gaseous medium.
  

Factors affecting diffusion :

• Relative atomic/ molecular mass: The lower Ar/ Mr, the faster the diffusion of the particles.
  
• Temperature: The higher the temperature, the more kinetic energy the particles have and the faster they move.
  

Next: Atomic Structure