States of Matter

States of Matter

All substances exist in one of three states of matter: solid, liquid, or gas. The state depends on how particles are arranged and how much energy they have.

 

The particle model

The particle model explains the properties of solids, liquids, and gases using simple spheres to represent atoms, molecules, or ions.

 

It describes:

  • Arrangement of particles
  • Movement of particles
  • Forces between particles
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Solids, liquids and gases

State

Arrangement

Movement

Forces

Solid

Particles tightly packed in a regular pattern

Vibrate in fixed positions

Strong forces

Liquid

Particles close together but irregular

Move around each other slowly

Weaker than solids

Gas

Particles far apart and random

Move quickly in all directions

Very weak forces

Changes of state

Substances can change from one state to another by gaining or losing energy.

Change

Name

Solid → Liquid

Melting

Liquid → Gas

Boiling / Evaporating

Gas → Liquid

Condensing

Liquid → Solid

Freezing

Solid → Gas

Sublimation

💡 Changes of state are physical changes – no new substances are made, and the process can be reversed.

 

Energy and state changes

  • Heating gives particles more kinetic energy
  • Cooling removes energy, so particles move less
  • Temperature stays constant during melting and boiling – energy is used to break or form bonds
 

Limitations of the particle model

  • Particles are not actually solid spheres – they can be atoms, ions, or molecules
  • Doesn’t show forces accurately
  • Doesn’t explain changes in size or shape
 

Despite this, the model is useful for explaining state changes and properties.

Questions 

  1. What are the three states of matter?
  2. What happens to particles when a solid melts?
  3. What is the name of the change from liquid to gas?
  4. Do particles get closer or further apart during condensation?
  5. Are changes of state physical or chemical?

Summary 

  • Substances exist as solids, liquids, or gases, depending on particle arrangement and energy
  • The particle model explains movement, spacing, and forces
  • Solids: fixed shape, strong forces
  • Liquids: flow, weaker forces
  • Gases: spread out, weak forces, fast-moving particles
  • State changes are physical changes and can be reversed