Periodic table

• Gallium was discovered 6 years after Mendeleev published his periodic table.

  Give two reason why the discovery of Gallium helped Mendeleev's table become accepted

  • Gallium's properties were correctly predicted by Mendeleev
  • Gallium fitted in a gap in Mendeleev's table
• Give two observations you could make when a small piece of Potassium is added to water

  (2 marks)

  • Potassium floats
  • Potassium melts
  • Potassium moves
  • Potassium becomes smaller
  • Lilac flame
  • Effervescence
• Explain why the reactivity of elements going down Group 1 changes

  (4 marks)

  • Reactivity increases
  • The outer shell electron is further away from the nucleus
  • So there is less attraction between the nucleus and outer shell
  • So the atom loses an electron more easily
• Explain why Sodium oxide has a high melting point

  (3 marks)

  • Giant ionic structure
  • with strong electrostatic forces of attraction between oppositely charged ions
  • so large amounts/lots of energy is needed to break the bonds/forces
• The plum pudding model did not have a nucleus

  Describe 3 other differences between the nuclear model of the atom and the plum pudding model

  (3 marks)

  • Nuclear model is mostly empty space
  • In the Nuclear model, the positive charge is all in the nucleus
  • In the Nuclear model, the mass is mostly concentrated in the nucleus whereas the mass is spread out in the Plum pudding model
  • In the nucleus, the electrons and the nucleus are separate
• Explain the trend in boiling points of the Halogens as you go down the group

  (4 marks)

  • Boiling point increases
  • because the size of the molecule increases
  • so the intermolecular forces increase
  • so more energy is needed to overcome the intermolecular forces