Chemistry

• States of matter


  Solids, liquids and gases. Liquids and gases are also called fluids.
• Solids


  • Particles fixed in regular lattice
  • Strong forces of attraction between particles
  • Definite shape
  • Vibrate about their positions
• Liquids


  • Particles randomly arranged and free to slide past each other - but stick close together
  • Weak forces of attraction between particles
  • Shape of container
  • Constantly and randomly moving
• Gases


  • Particles far apart - move fast and free in all directions
  • Very weak forces of attraction between particles
  • Shape of container
  • Constantly and randomly moving in straight lines
• State symbols


  • (s) solid
  • (l) liquid
  • (g) gas
  • (aq) aqueous
• Melting


  1. Solid heated, particles gain more energy, vibrate more and weaken bonds

  2. Solid expands until particles break free and turn into liquid

  3. Occurs at melting point
• Boiling/Evaporating


  1. Liquid heated, particles gain more energy, move more and faster, forces holding liquid together weaken

  2. Liquid turns into gas

  3. Occurs at boiling point
• Subliming


  Solid turns directly into gas
• Condensing


  Gas turns into liquid as there is not enough energy to overcome forces of attraction
• Freezing


  Liquid turns into solid as there is not enough energy to overcome forces of attraction
• The amount of energy needed for a substance to change state depends on how strong the forces between particles are
• Diffusion


  Movement of particles from high concentration to low concentration, occurs in liquids and gases
• Experiments demonstrating diffusion


  • Potassium permanganate (VII) in water
  • Ammonia and hydrogen chloride
  • Bromine gas and air
• Solution


  A mixture of a solute and a solvent that does not separate out
• Solute


  The substance being dissolved
• Solvent


  The liquid the solute is dissolving into
• Saturated solution


  A solution in which no more solute can dissolve
• Proton


  • Relative mass 1, Charge +1, Found in nucleus
• Neutron


  • Relative mass 1, Charge 0, Found in nucleus
• Electron


  • Relative mass 0.0005, Charge -1, Orbiting outside the nucleus
• Atom is always electrically neutral - No. of protons = no. of electrons
• Isotopes


  Different forms of the same element, with the same number of protons but different number of neutrons
• Relative atomic mass (Ar)


  The average mass of all the isotopes of the element, compared to the mass of one atom of carbon 12
• Element


  Consists of only 1 type of atom, represented by 1 or 2 symbols
• Compound


  Substance formed when two or more elements are chemically bonded together
• Mixture


  Components are not chemically joined, can be separated by physical methods
• Pure substance


  Made up of a single element or compound, has a specific sharp melting and boiling point
• Filtration


  Separate an insoluble solid from a liquid OR to purify a product by separating out the impurities from it
• Crystallisation


  Separate a soluble solid from a solution by heating the solution to concentrate it, then cooling to form crystals
• Experiment to separate rock salt

  • Grind up, dissolve in water, filter, evaporate to leave pure salt crystals
• Chromatography


  Used to separate different dyes in an ink
• Chromatography method


  Draw pencil line on filter paper, add ink spots, place in solvent, solvent travels up paper separating dyes
• Rf value


  Ratio between distance travelled by substance and distance travelled by solvent
• Standard reference materials (SRMs)

  Pure samples of substances used to check identities of components in a mixture
• Simple distillation


  Separate a mixture of liquids with very different boiling points, liquid with lowest boiling point evaporates first
• Fractional distillation


  Separate a mixture of liquids with similar boiling points, liquids evaporate and condense at different heights in the column
• Mendeleev arranged elements in periodic table by atomic mass but left gaps for undiscovered elements
• Groups (columns)


  Elements have similar properties because they have the same number of electrons in their outer shell
• Periods (rows)


  Elements have the same number of electron shells
• Electron shells/energy levels


  Lowest energy shell filled first, only certain number of electrons allowed in each shell