Topic 1

• Atoms


  Make up all substances. Are the smallest part of an element that can exist.
• Compounds


  Formed from elements by chemical reactions.
• Mixture


  Consists of two or more elements or compounds not chemically combined together. They can be separated.
• History of the atom:

  • Early 1800s Dalton thought they were tiny spheres which couldn't be divided.
  • Late 1800s Thompson discovered the electron and proposed the plum pudding model.
  • Early 1900s Rutherford conducted gold foil experiment and discovered the positive nucleus. Proposed nuclear model.
  • Couple years later Bohr suggested that electrons orbit the nucleus in shells. He also discovered the proton.
  • Few years later Chadwick discovered neutrons.
• What order were the parts of the atom discovered?

  1. electron
  2. proton
  3. neutron
• Plum pudding model


  Depicted an atom as a ball of positive charge with negative electrons embedded in it.
• Rutherford scattering experiment


  Positively charged alpha particles fired at thin gold foil. Most particles went straight through but a few scattered in different directions, giving evidence for the positively charged nucleus.
• Atomic number


  The number of protons in an atom of an element.

  Bottom number of element on periodic table.
• Atoms of different elements have a different number of:

  Protons
• Atom has an overall charge of:

  0 (Protons and electrons cancel each other out)
• Relative charges


  Proton = +1

  Neutron = 0

  Electron = -1
• Relative mass of atoms


  Proton = 1

  Neutron = 1

  Electron = Very small
• Mass number =


  Protons + Neutrons

  Top number of element on periodic table.
• Isotopes


  Atoms of the same element with different numbers of neutrons. For example Chlorine.
• Relative atomic mass (Isotopes)

  (% isotope A * mass isotope A) + (% isotope B * Mass isotope B)

  ---------------------------------------------------------

  100
• How many electrons can each cell hold?

  First shell = 2

  Second shell = 8

  Third shell = 8
• Period (Row)


  Tells us how many shells of electrons an element has.
• Group (column)


  Tells us how many outer electrons an element has.
• Half equations


  Shows what happens to electrons in reactions which lose or gain electrons.
• Ionic equations


  Used to show what happens to ions during reactions.
• Filtration


  When you separate substances by filtering.
• Crystallisation

  • Heat an evaporating dish on water bath.
  • Heating stopped when solution is at the point of crystallisation.
  • Evaporating basin then left to evaporate leaving just crystals.
• Simple distillation

  • Solution is heated and liquid evaporates.
  • Produces a vapour which passes through a condenser where in condenses.
  • After all liquid is evaporated you are left with the separated solid and liquid.
• Fractional distillation:

  • Solution is heated to the temp of substances lowest boiling point.
  • Substance will rise and evaporate first, where the vapour will pass the condenser and condense .
  • This is repeated until all substances are seperated.
• Chromatography

  • Pencil line drawn on chromotography paper and spots of coloured inks placed on.
  • Paper then put in beaker of water where pencil line is above water.
  • Water travels up the paper seperating the inks showing the different components.
• Solution


  Mixture formed by a solute and a solvent.
• Solute


  The substance that's dissolved in a solution.
• Solvent


  The liquid in which the solute dissolves to form a solution
• Why do elements in the same periodic group have similar chemical properties?

  They have the same amount of electrons in their outer shell.
• History of the periodic table

  • John Newlands ordered his table by atomic weight
  • Mendeleev ordered his table by atomic mass and left gaps for undiscovered elements.
  • Elements with properties predicted by Mendeleev were discovered and filled in the gaps
  • Finally elements were ordered by atomic number
• Why did Mendeleev's table not make complete sense

  He didn't know about isotopes so order on atomic weights was not always correct.
• Metals

  Elements which react to form positive ions
• Non - Metals

  Elements that don't form positive ions
• Metals

  Elements that lose electrons in reactions
• Non-metals

  Elements that gain electrons in reactions.
• Descending groups

  As you go down the group the outer shell of electrons become further away from the nucleus and so weakens their attraction to the nucleus.
• Attraction

  The weaker the attraction of outer electrons to the nucleus the more easily it can react and lose its outer electrons.
• Electrical conductivity

  Metals are good conductors of electricity

  Non-metals are bad conductors of electricity
• Physical characteristics of metals

  • Usually shiny
  • Solid at room temperature (excluding mercury)
  • Malleable
  • Ductile
  • High melting and boiling points.
• Physical characteristics of non-metals

  • Dull and non reflective.
  • Different states at room temperature
  • Brittle
  • Low melting and boiling points