Atomic Structure and Periodic Table

• a pure substance consists only of one element or one compound
• Filtration is used to separate an insoluble solid from a liquid.

  - separating sand from a mixture of sand and water

  • excess reactant from a reaction mixture.
• Crystallisation is used to produce solid crystals from a solution

  • put the solution in an evaporating basin
  • warm the solution by placing the evaporating basin over a boiling water bath
  • stop heating when crystals begin to form around the edge of the basin
  • After the remaining solution has cooled down, pour the excess liquid away (or filter it).
  • Dry the crystals using a warm oven or by patting them with filter paper.
• Simple distillation is used to separate a solvent from a solution.

  • produces pure water from seawater.
  • Simple distillation works because the dissolved solute has a much higher boiling point than the solvent.
  • When the solution is heated, solvent vapour leaves the solution.
  • It moves away and is cooled and condensed.
  • The remaining solution becomes more concentrated as the amount of solvent in it decreases.
• Paper chromatography is used to separate mixtures of solublesubstances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.

  • the stationary phase - paper
  • the mobile phase is the solvent that moves through the paper - water
• J J Thomson = discovered the electron.

  • This led him to suggest the plum pudding model of the atom. - In this model, the atom is a ball of positive charge with negative electrons embedded in it 
• 1909 - Ernest Rutherford tested the plum pudding model.

  • positively charged alpha particles were fired at thin gold foil.
  • Most alpha particles went straight through the foil.
  • But a few were scattered in different directions.
  • led him to suggest the nuclear model

  ——-> the mass of an atom is concentrated at its centre, the nucleus

  • the nucleus is positively charged
• Niels Bohr suggested that electrons orbit the nucleus in shells.

  • The shells are at certain distances from the nucleus.
  • nucleus contained small particles, called protons. Each proton has a small amount of positive charge.
• 1932 - James Chadwick discovered the neutron
• Mass number = top = protons and neutrons

  Atomic number = bottom = protons/ electrons

  
• Isotope = atoms of the same element with the same number of protons but different number of neutrons

  • same atomic number
  • different mass number
• Mendeleev = created the periodic table (1869)

  • he arranged the elements in order of increasing atomic weights.
  • He also took into account the properties of the elements and their compounds. This meant that his table:
  • had gaps in it
  • showed elements with similar chemical properties lined up in groups

  Why was his periodic table accepted?

  Elements with properties predicted by Mendeleev were discovered

  • filled the gaps in his table
• Properties of Metals and Non-metals

  Metals

  • good conductor of electricity
  • good conductor of heat
  • shiny
  • high density
  • ductile

  Non-metals

  • poor conductor of electricty
  • poor conductor of heat
  • dull
  • low density
  • brittle
• Group 0 - noble gases

  • low boiling point + increases going down the group ——> atoms become larger, intermolecular forces become stronger so more energy is needed to overcome these forces
  • they are unreactive
• Group 1 - alkali metals

  • they are soft
  • low melting points
  • low densities
  • reactivity increases as you go down the group

  What are the observations for LI, Na and K?

  lithium : fizzes, becomes smaller and disappeares

  sodium: fizzes rapidly, melts to form a ball, smaller and disappears

  potassium: burns violently with sparks + lilac flame, quickly melts, disappears with small explosion
• Group 1 - chemical reactions

  They react with oxygen to make metal oxides:

  • The alkali metals burn vigorously when heated and placed in a gas jar of oxygen
  • The oxide forms as white smoke
  • reactions becomes more vigorous going down the group

  Reaction with chlorine:

  • react vigorously
  • chlorides are white solids ——> form colourless solution
• Group 7 - Halogens

  • Melting point and boiling point increases as you go down the group
  • Molecules become larger
  • intermolecular forces are stronger
  • more energy is needed to break/overcome these forces


  At room temp:

  Chlorine ——> pale green ——> gas

  bromine ——> brown ——-> liquid

  iodine ——> purple-black ——> solid
• Group 7 - chemical properties


  Halogen + metal ——> salt

  Halogens react with iron wool:

  Fluorine: cold iron wool burns ——> white iron(III) fluoride

  Chlorine: hot iron wool burns vigorously ——> orange-brown iron(III) chloride

  Bromine: hot iron wool burns quickly ——> red-brown iron(III) bromide

  Iodine: hot iron wool reacts slowly in iodine vapour ——> grey iron(II) iodide
• Transition metals


  • they conduct electricity in the solid and liquid states
  • they are shiny when freshly cut
  • higher melting points
  • higher densities
  • greater strength
  • greater hardness