science sec 1 rev

• Particulate nature of matter

  The arrangement and motion of particles and the attractive forces between them
• States of matter


  • Solid
  • Liquid
  • Gas
• Solid


  • Closely packed
  • Orderly arrangement
  • Vibrate at fixed position
  • Very strong attractive forces
• Liquid


  • Less closely packed
  • Disorderly arrangement
  • Move freely by sliding over each other
  • Strong attractive forces
• Gas


  • Far apart
  • Disorderly arrangement
  • Move rapidly and in random direction
  • Very weak attractive forces
• Solids have a fixed shape
• Liquids have no fixed shape
• Gases have no fixed shape
• Solids have a fixed volume
• Liquids have a fixed volume
• Gases have no fixed volume
• Solids cannot be compressed
• Liquids cannot be compressed
• Gases can be compressed
• Liquids can flow
• Gases can flow
• Why solids have fixed shapes and volumes

  The particles of solids are held in fixed positions and do not move out of these positions
• Why liquids can flow


  The particles of liquids are not held in fixed positions and can slide over each other easily
• Why gases can be compressed

  There are many air spaces as particles of gases are spread out
• Expansion and Contraction


  1. Heating solid: particles gain energy and vibrate faster

  2. Cooling solid: particles lose energy and vibrate slower
• When a solid is heated


  Its particles gain energy and vibrate faster
• When a solid is cooled


  Its particles lose energy and vibrate slower
• Melting and Boiling


  1. Heating solid: particles gain energy and overcome forces of attraction

  2. Heating liquid: particles gain energy and slide past one another
• Freezing and Condensation

  1. Cooling liquid: particles lose energy and slide past one another slower

  2. Cooling gas: particles lose energy and move slower
• Diffusion


  The net movement of particles from a region of higher concentration to a region of lower concentration
• Particles of solids cannot diffuse
• Factors affecting Rate of Diffusion

  • Temperature
  • Relative molecular mass (M.) of a gas
• The higher the temperature

  The higher the rate of diffusion
• Relative molecular mass


  The average mass of one molecule of a covalent compound compared with 1/12 the mass of a carbon-12 atom
• Gases with lower relative molecular masses diffuse faster
• Transport systems are necessary in multicellular organisms
• Essential substances


  Nutrients and oxygen
• Metabolic waste products


  Carbon dioxide, urea, excess water molecule
• Multicellular organisms require a transport system to transport essential nutrients to, and waste products from, all its cells
• Unicellular organisms do not require transport systems
• Surface area to volume ratio

  6.0
• Unicellular organisms have a large surface area-to-volume ratio which allows substances to diffuse across the cell membrane
• Diffusion


  The net movement of molecules from a region of higher concentration to a region of lower concentration
• Osmosis


  The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane
• Large multicellular organisms cannot rely on diffusion alone to supply their cells with substances