Groups in the periodic table

• Periodic table


  • Ordered by increasing atomic number
  • Elements in the same group (column) have the same number of outer shell electrons
  • Elements in the same period (row) have the same number of electron shells
• Group 1 elements


  One electron in the outer shell
• Elements in the same group

  • Have similar chemical properties
• Alkali metals


  Group 1 elements
• Alkali metals


  • Relatively low melting points
  • Soft
• Alkali metals


  React with water to form alkaline solutions (pH greater than 7)
• Reaction of lithium with water

  Lithium hydroxide and hydrogen produced
• Reaction of sodium with water

  2Na + 2H2O → 2NaOH + H2
• Storing alkali metals


  In oil to prevent reaction with water vapour and oxygen in the air
• Reaction of lithium with water

  • Slowest reaction of alkali metals
  • Bubbles of hydrogen produced
  • Doesn't melt (highest melting point)
• Reaction of sodium with water

  • Faster reaction than lithium
  • Floats on surface of water
  • Bubbles of hydrogen produced causing sodium to whizz around
  • Melts as enough energy given out to meet sodium's melting point
• Reaction of potassium with water

  • More violent reaction than sodium
  • Bubbles of hydrogen produced causing potassium to whizz around
  • Melts into a shiny ball
  • Burns with a lilac flame
• Order of reactivity of first 3 alkali metals with water

  • Lithium
  • Sodium
  • Potassium
• Reactivity increases down group 1
• Increasing reactivity down group 1

  More electron shells, more electron shielding, weaker attraction between positive nucleus and outer shell electron, easier to remove outer shell electron to form positive metal ion
• Francium would react most violently with water
• Halogens


  Group 7 elements, have 7 outer shell electrons
• Chlorine at room temperature

  Pale green gas
• Bromine at room temperature


  Red-brown liquid
• Iodine at room temperature

  Black solid
• Trend of halogens down the group

  Melting and boiling point increases, so state changes from gas to liquid to solid
• Fluorine would be a gas and astatine would be a solid at room temperature
• You go down the group

  Melting and boiling point increases
• Fluorine is above chlorine so should have a boiling point lower than chlorine. This means it would be a gas at room temperature.
• Astatine is below iodine in group 7 so should have a higher melting point than iodine. Therefore you can predict that it would be a solid at room temperature.
• Why does melting and boiling point increase down Group 7?

  The molecules get bigger down the group so there are more intermolecular forces to overcome during melting / boiling so more energy is required.
• Chemical test for chlorine


  Damp litmus paper placed into a test tube of gas. If chlorine is present, the litmus paper will turn red then white due to the bleaching effect of chlorine.
• Halogens are diatomic


  They form molecules consisting of 2 atoms
• Halide ion charge


  • 1, they gain one electron to have a stable electron configuration
• What is produced when a halogen reacts with a metal?

  Metal halide salt
• Reaction between bromine and sodium

  Br2 + 2Na → 2NaBr
• Reaction between chlorine and calcium


  Cl2 + Ca → CaCl2
• Magnesium fluoride (MgF2) is the product of the reaction between magnesium and fluorine
• Reaction between iodine and potassium

  Iodine + potassium → Potassium iodide
• Trend in reactivity of the halogens

  Reactivity decreases down group 7. Rate of reaction decreases down group 7.
• What is formed when hydrogen reacts with a halogen?


  Hydrogen halides, e.g. HCl, HBr...
• Chlorine reacts with hydrogen in the presence of sunlight but bromine requires a flame. This is because reactivity decreases down the group so bromine requires more energy for the reaction to occur.
• What is formed when a hydrogen halide dissolves in water?

  An acidic solution. Hydrogen ions dissociate, making the solution acidic.
• Reaction between hydrogen and chlorine

  H2 + Cl2 → 2HCl
• Hydrogen fluoride (HF) is the product of the reaction between hydrogen and fluorine