States of Matter & Properties of Substances

The three states of matter

• The particle model shows particles as small solid spheres
• In a solid the particles are close together in a regular pattern and vibrate in place; in a liquid they are close but move past each other; in a gas they are far apart and move quickly in all directions

• Melting and freezing happen at the melting point; boiling and condensing happen at the boiling point
• The energy needed to change state depends on the strength of the forces between the particles. The stronger the forces, the higher the melting and boiling points
• What those particles and forces are depends on the type of bonding and structure of the substance
• To predict a state from data: below the melting point, solid; between the melting and boiling points, liquid; above the boiling point, gas
• A single atom does not have bulk properties: one atom of iron is not "hard" or "shiny"; those properties belong to the whole structure
• (HT) Limitations of the simple model: real particles are not solid spheres, and the model shows no forces between particles, so it cannot on its own explain why changes of state need energy