Atomic structure & the periodic table

• What is an element?

  All the atoms are the same.
• What defines a compound?

  Contains 2 or more different elements combined.
• How do compounds differ from their constituent elements?

  Compounds have different properties than elements.
• What is a mixture?

  Not chemically joined and can be separated physically.
• What is a molecule?

  Any elements combined, even the same element.
• What are physical separation techniques used for?

  • Separate mixtures
  • Cannot separate elements in compounds
• What is filtration used for?

  To separate an insoluble solid from liquid.
• What equipment is needed for filtration?

  • Conical Flask
  • Filter paper
  • Filter funnel
• What are the steps in the filtration process?

  1. Pour mixture into filter paper.
  2. Liquid passes through filter paper.
  3. Solid is trapped in filter paper.
  4. Liquid is separated from solid.
• What is crystallisation used for?

  To separate a soluble solid from a liquid.
• What are the steps in the crystallisation process?

  1. Leave solution out to evaporate water.
  2. Crystals of solid solution form.
  3. Gently heat to speed up evaporation.
  4. Some chemicals may break down if heated.
• What is simple distillation?

  Evaporate liquid and condense vapour back to liquid.
• What are the steps in simple distillation?

  1. Place solution in flask.
  2. Connect flask to glass tube.
  3. Surround tube with condenser.
  4. Heat solution with Bunsen burner.
  5. Collect liquid in beaker.
• How is drinking water produced using simple distillation?

  By evaporating sea water and condensing vapour.
• Why is simple distillation not commonly used for drinking water?

  It requires a great deal of energy.
• What is fractional distillation used for?

  • Separate mixtures of liquids
  • Based on different boiling points
• What are the steps in fractional distillation?

  1. Gently heat mixture.
  2. Lower boiling point liquid evaporates first.
  3. Vapours rise in fractionating column.
  4. Repeated evaporation and condensation occurs.
  5. Collect liquid in fresh beaker.
• What happens when the temperature stops rising during fractional distillation?

  Only one chemical is passing through the condenser.
• What is the effect of similar boiling points on fractional distillation?

  It becomes harder to separate the liquids.
• What is paper chromatography used for?

  • Separate mixtures
  • Based on different solubilities
• What are the steps in paper chromatography?

  1. Draw a line on chromatography paper.
  2. Place dots of different colours on the line.
  3. Immerse paper in solvent.
  4. Observe how far the colours travel.
• What indicates a pure substance in paper chromatography?

  One dot of colour on the paper.
• What indicates a mixture in paper chromatography?

  Two or more separate dots of colour.
• What is the role of the stationary and mobile phases in chromatography?

  • Stationary phase: paper
  • Mobile phase: solvent
• What was the plum pudding model?

  Negative electrons embedded in positive charge.
• What did the alpha scattering experiment demonstrate?

  • Atoms are mainly empty space.
  • Centre of atom has positive charge.
  • Centre contains a great deal of mass.
• What is the central part of an atom called?

  Nucleus
• What is the nuclear model of atomic structure?

  • Positive nucleus contains most mass.
  • Mostly empty space.
  • Negative electrons orbit nucleus.
• Who proposed that electrons orbit the nucleus at specific distances?

  Niels Bohr
• Who discovered neutrons in the nucleus?

  James Chadwick
• What is the radius of an atom?

  $0.2 \text{ nanometers} (1 \times 10^{-9} \text{ m})$
• What is the radius of a nucleus?

  $1 \times 10^{-14} \text{ m}$
• What are the relative masses of protons, electrons, and neutrons?

  • Proton: 1
  • Electron: very small
  • Neutron: 1
• What does the atomic number represent?

  Number of protons in an atom.
• What does the mass number represent?

  Total number of protons and neutrons.
• What are isotopes?

  Atoms of the same element with different neutrons.
• What are ions?

  Atoms with an overall charge due to electrons.
• What are the groups in the periodic table?

  • Group O: Noble Gases
  • Group 7: Halogens
  • Group 1: Alkali metals
• Who arranged atoms in order of increasing atomic weight?

  Newland
• What did Mendeleev do for the periodic table?

  Developed the first modern periodic table.