Topic 6: Groups in the Periodic Table

• Group 1 Metals:

  • alkali metals (lithium, sodium, potassium)
  • soft
  • low melting/boiling points
  • form ionic compounds (outer electron is easily lost so cannot form covalent bonds)
• Alkali metals readily lose their outer electron to form a 1+ ion with a stable electronic structure (more easily lost means more reactive)

  • more reactive down group 1
  • outer electron is further from the nucleus (larger atomic radius)
  • not strongly attracted and less energy is needed to break the forces of attraction
• When alkali metals are put in water, they react more vigorously to produce a hydroxide of the metal and hydrogen gas:

  • Lithium will move around the surface with lots of effervescence
  • Sodium does the same as lithium but also melts and disappears in the heat
  • Potassium does the same as sodium but ignites the hydrogen gas in the heat which produces a lilac flame
• Group 7 elements are the halogens like chlorine, bromine and iodine. Down the group, melting/boiling points increase:

  • Chlorine is a fairly reactive green gas
  • Bromine is a poisonous red-brown liquid which releases orange vapour at room temperature
  • Iodine is a dark grey crystalline solid which releases purple vapour when heated

  Halogen colours get darker down the group.

  All have 7 outer shell electrons so chemical properties are similar and exist as diatomic molecules
• A halogen atom only needs to gain 1 electron to form a 1- ion with a stable electronic structure so the easier it is to attract an electron the more reactive it is.

  Reactivity decreases down the group as its harder to attract an extra electron when its further from the nucleus (forces of attraction weaken as atomic radius is larger)
• Halogens reacts vigorously with some metals to form salts called metal halides.

  They can also form hydrogen halides that are soluble and dissolve in water to form acidic solutions (hydrochloric acid)
• Group 7 elements participate in displacement reactions meaning a more reactive halogen displaces a less reactive halide ion in a compound.

  This is a redox reaction as the halogen reduces (gains electrons) while the halide ion oxidated (losses electrons).
• Halogen Reactivity Order:

  1. Chlorine
  2. Bromine
  3. Iodine
• Halogen Displacement Reactions Practical:

  1. Measure a small amount of halide salt solution in a test tube
  2. Add a few drops of halogen solution and gently shake
  3. A colour change indicates that the halogen has displaced the halide ion

  • chlorine water + potassium bromine ---> colourless (Cl2) to orange (Br2)
  • chlorine water + potassium iodide ---> colourless to brown (I2)
  • bromine water + potassium iodide ---> orange to brown
• Group 0 elements are noble gases:

  • colourless at room temperature
  • monoatomic
  • inert (full outer shell means no need to lose/gain electrons)
  • non-flammable
• Noble gases are difficult to observe but have many uses:

  • Argon - stops filament in lamps from burning away and protects metals being welded by providing an inert atmosphere
  • Helium - prevents metals being welded by preventing O2 reacting, airships and party balloons as they're safer than H2
  • Krypton/Xenon - flash photography

  Melting/boiling points and density increases down Group 0 as well as sharing similar chemical properties because of electron structures