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 of alkali metals)
• Reaction of sodium with water

  • Faster reaction than lithium
  • Floats on surface of water (less dense than water)
  • Bubbles of hydrogen produced which cause sodium to whizz around
  • Melts as enough energy is given out to meet sodium's melting point
• Reaction of potassium with water

  • More violent reaction than sodium
  • Bubbles of hydrogen produced which cause 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 halogen states down the group

  Melting and boiling point increases, so chlorine is gas, bromine is liquid, iodine is solid at room temperature
• Fluorine would be a gas and astatine would be a solid at room temperature
• You go down the group

  Melting and boiling point increases
• What state would you expect the halogens fluorine and astatine to be at room temperature?
• Fluorine


  Above chlorine in group, so should have a boiling point lower than chlorine, meaning it would be a gas at room temperature
• Astatine


  Below iodine in group 7, so should have a higher melting point than iodine, therefore 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
• Diatomic


  They form molecules consisting of 2 atoms, e.g. Cl2, Br2
• Halide ion charge


  • 1, they gain one electron to have a stable electron configuration
• Product of halogen reacting with metal

  Metal halide salt
• Reaction between bromine and sodium

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


  Cl2 + Ca → CaCl2
• Reaction between iodine and potassium

  Iodine + potassium → Potassium iodide
• Hydrogen reacting with a halogen

  Hydrogen halides, e.g. HCl, HBr
• Hydrogen halide dissolving in water

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

  H2 + Cl2 → 2HCl
• Halogen displacement reaction


  When a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
• Halogens chlorine can displace from an aqueous ionic solution


  Chlorine can displace any halogens below it in group 7, it will displace iodine and bromine
• Halogens bromine can't displace from an aqueous ionic solution

  Bromine can't displace any halogens above it in group 7, these are chlorine and fluorine
• Reaction between chlorine and potassium bromide

  Chlorine + potassium bromide → potassium chloride + bromine