Chapter 8: Matter and Changing of State

8.1-States of Matter

The three states of matter-solid, liquid and gas

• Materials come in three different forms-solid, liquid and gas.
• Which state something is at a certain temperature depends on how strong the forces of attraction are between the particles of the material
• How strong the forces are depends on three things
  • The material(the structure of the substance, and the type of bonds holding the particles together)
  • The temperature
  • The pressure

Particles theory:

• Solids
  • In solids, there are strong forces of attraction between particles, which holds them close together in fixed positions to form a very regular lattice arrangement
  • The particles don’t move from their positions, so all solids keep a definite shape and volume and don’t flow like liquids
  • The particles vibrate about their positions, the hotter the solid becomes, the more they vibrate(causing solids to expand slightly when heated)
• Liquids
  • In liquids, there’s a weak force of attraction between the particles
  • They’re randomly arranged and free to move
  • Definite volume but don’t keep a definite shape
  • Constantly moving with a random motion, hotter the liquid faster they move
• Gases
  • In gases, the force of attraction is very weak
  • Free to move and far apart
  • Constantly moving with a random motion

State symbols tell you the state of a substance in an equation

• Solid-s
• Liquid-l
• Gas-g
• Aqueous(means dissolved in water)-aq

8.2-Changing State

Substances can change from one state to another

• Physical changes don’t change the particles-just their arrangement or their energy
  • When a solid is heated, its particles gain more energy
  • This makes the particles vibrate more, which weakens the forces that hold the solid together
  • At a certain temperature, called the melting point the particles have enough energy to break free from their positions, called melting and turns a solid to an liquid
  • When a liquid is heated, again the particles get even more energy
  • This energy makes the particles move faster, which weakens and breaks the bonds holding the liquid together
  • At a certain temperature, called the boiling point, the particles have enough to break their bonds
  • This is evaporating, and the liquid becomes a gas
  • As a gas cools, the particles no longer have enough energy to overcome the forces of attraction between them
  • Bonds form between the particles
  • At the boiling point, so many bonds have formed between the gas particles that the gas becomes a liquid, this is called condensing
  • When a liquid cools, the particles have less energy so move around less
  • There’s not enough energy to overcome the attraction between the particles, so more bonds form between them
  • At the melting point, so many bonds have formed between the particles that they’re held in place
  • The liquid becomes a solid and this is called freezing

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