Structure 1.1 (from kognity)

• Pure substances


  Elements and compounds
• Elements


  The simplest forms of matter, consisting of only one type of atom
• Elements


  • Cannot be broken down chemically into simpler substances
  • Atoms can exist individually or bonded together
• Compounds


  Pure substances composed of two or more different elements chemically combined in fixed ratios
• Mixtures


  Composed of two or more elements or compounds in no fixed ratio, can be separated by physical methods
• Types of mixtures


  • Homogeneous
  • Heterogeneous
• Homogeneous mixtures


  • Air
  • Salt water
• Heterogeneous mixtures


  • Oil and water
  • Carbonated water
  • Iron and sulfur
• Filtration


  Separation of an insoluble solid from a liquid or solution
• Evaporation


  Separation of a solute from a solvent by heating to evaporate the solvent
• Solvation


  Separation of a heterogeneous mixture of two solids based on differences in solubility
• Distillation


  Separation of a liquid mixture based on differences in volatility or boiling points
• Paper chromatography


  Separation of a mixture of solutes in a solvent based on differences in solvation
• Recrystallisation


  Purification of a solid by dissolving it in a solvent, filtering, and then cooling to recrystallise the pure product
• States of matter


  Solid, liquid, gas
• Solid


  • Particles held in fixed positions, can vibrate around a fixed point
  • Cannot be compressed
  • Have fixed shape and volume
  • Cannot flow
• Liquid


  • Particles more spread out but still attracted to each other
  • Cannot be compressed
  • Have fixed volume but not fixed shape
  • Can flow
• Gas


  • Particles very spread out and move randomly in straight lines
  • Can be compressed
  • Have no fixed shape or volume
• Kinetic molecular theory


  • All matter is made up of small particles with kinetic energy that causes constant motion
  • Kinetic energy is proportional to temperature
• Density


  Mass per unit volume
• Solids tend to have higher densities than liquids, which tend to have higher densities than gases
• Changes of state


  Physical changes where a substance changes from one state to another
• Celsius scale


  Based on the freezing (0°C) and boiling (100°C) points of water
• Kelvin scale


  Absolute temperature scale where 0 K is absolute zero, particles have zero kinetic energy
• Temperature in Kelvin


  Directly proportional to the average kinetic energy of the particles
• ºC to K = +273, K to ºC = -273
• Types of matter


  • Elements
  • Compounds
  • Mixtures
• Mixtures can be separated relatively easily using different separation techniques
• Changes of state are physical changes, no new substances are produced
• Gases have the greatest amount of kinetic energy, solids have the least