Topic 6

• 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
• Reactivity of first 3 alkali metals with water

  Lithium reacts least violently, potassium reacts most violently: Lithium < Sodium < Potassium
• Reactivity increases down group 1
• Reason for increasing reactivity down group 1

  Number of electron shells increases, 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 in states of halogens at room temperature

  Chlorine is gaseous, bromine is liquid, iodine is solid because they have different melting and boiling points. As you go down the group, melting and boiling point increases.
• Fluorine would be a gas at room temperature, astatine would be a solid at room temperature
• Reason for increasing melting and boiling point down group 7

  Increasing atomic size, more electron shells, weaker intermolecular forces
• 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.
• 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
• When a halogen reacts with a metal, a metal halide salt is produced
• Reaction between bromine and sodium

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


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

  Iodine + potassium → Potassium iodide
• Reactivity of halogens


  Decreases down group 7, rate of reaction decreases down group 7
• Hydrogen halides


  Formed when hydrogen reacts with a halogen, e.g. HCl, HBr
• When a hydrogen halide dissolves in water, an acidic solution is formed as hydrogen ions dissociate
• Reaction between hydrogen and chlorine

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


  Occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide