S1 - Models of the particulate nature of matter

• Elements cannot be broken down chemically into simpler substances
• Compounds consist of atoms of different elements chemically bonded in a fixed ratio.
• Mixtures contain more than one element or compound, not chemically

  bonded and so can be separated by physical methods.
• Solvation separates two heterogenous solids like sand and salt by dissolving one of the solids in water.
• Filtration separates an insoluble solid from a solute.
• Evaporation separates a soluble solid from a solute.
• Fractional distillation separates two liquids with different boiling points.
• Recrystallization separates impurities from a mixture of solids.
• Paper chromatography separates a mix of solutes in a solvent.
• A homogenous mixture is a mixture that has a uniform composition, it is difficult to identify individual components.
• A heterogenous mixture has a non-uniform composition, the components are in clumps (müsli + milk)
• Freezing is going from liquid to solid
• Melting is going from solid to liquid
• Condensation is going from gas to liquid
• Boiling is going from liquid to gas
• Solids

  • Particles cannot move freely
  • Particles vibrate around a fixed point
  • Cannot be compressed
  • Cannot flow
• Liquids

  • Particles are spread out
  • Arranged randomly
  • Can be compressed
  • Can flow
• Gases

  • Particles are very spread out
  • Can be compressed
  • Can flow
• Sublimation is going from a solid to a gas
• Deposition is going from a gas to a solid
• Temperature (K) is a measure of the average kinetic energy of particles.
• Freezing, condensation and deposition are exothermic reactions.
• Melting, evaporation/ boiling and sublimation are endothermic reactions.
• Celcius = Kelvin - 273
• Atoms contain a positively charged nucleus made of protons and neutrons.
• Electrons occupy the space around the nucleus of an atom
• Protons have a relative mass of 1 and a relative charge of +1
• Neutrons have a relative mass of 1 and a relative charge of 0
• Electrons have a negligible mass and a relative charge of -1
• The mass number is the bigger number and is the number of protons + neutrons
• The atomic number is the number of protons and electrons
• Isotopes are atoms of the same elements that have a different number of neutrons
• Isotopes have the same chemical properties as these are related to the number of electrons.
• Isotopes have different physical properties like density, boiling and melting point etc.
• The relative atomic mass of an element is the weighted average of the masses of its isotopes relative to 1/12 of the mass of a carbon-12 atom.
• Mass spectra are used to determine the relative atomic masses of elements from their isotopic composition.
• The element is Pb and the relative atomic mass is 207.2

  
• Emission spectra are produced by atoms when electrons in excited states return to a lower energy level
• The red part of the emission spectra has the longest wavelength, lowest energy and lowest frequency.
• The purple part of the emission spectra has the shortest wavelength, highest energy and highest frequency.