Group 2

• Group 2 elements are called the alkaline earth metals. They have metallic bonding.
• Metallic bond - the electrostatic attraction between positive metal ions and delocalised electrons.
• Atomic Radius increases down the group
• First ionisation energy - the amount of energy required to remove one mole of electrons from one mole of atoms in its gaseous state.
• First ionisation energy decreases down the group
• Melting point decreases down the group
• Reactivity increases down the group
• Magnesium reacts slowly with cold water

  Observations: Thick white PPT & small bubbles

  pH: 8
• Magnesium reacts vigorously with steam (in absence of air)

  Observations: Bright white light, MgO (white powder)
• Calcium with Water

  Observations: White PPT & effervescence

  pH: 9-10
• Strontium with water

  Observations: thin white ppt & effervescence

  pH: 10-11
• Barium with water

  Observations: colourless solution and effervescence

  pH: 13
• The solubility of the metal hydroxides increases down the group.
• Magnesium with sulphuric acid

  colourless solution
• Calcium with sulphuric acid

  thin white ppt
• Strontium with sulphuric acid

  white ppt
• Barium with sulphuric acid

  thick white ppt
• Test for sulphate ions:

  1. Add 1cm3 dilute HCl to 1cm3 test sol. in a test tube - removes any contaminating ions that may form a PPT (e.g. CO3)
  2. Add 1cm3 BaCl2

  Observations: thick white ppt
• Test for hydroxide ions:

  Add 1cm3 of Mg(NO3)2 to 1cm3 of test solution in a test tube.

  Observation: thick white PPT
• The test for sulphate and hydroxide ions can be used in reverse to identify the group 2 metal ions.
• Test for Ba or Sr

  Add Na2SO4 or H2SO4, white PPT
• Test for Ca or Mg

  add NaOH, white PPT
• Magnesium is used to extract titanium from its ore TiO2

  1. TiO2 is converted into TiCl4 and then reduced to Ti by a reaction with magnesium
• Magnesium hydroxide is sparingly soluble so it is sold as a suspension in water. Known as 'milk of magnesia' . It is taken to alleviate constipation and as an antiacid to neutralise excess acid in the gut. It doesn't irritate the oesophagus as it's slightly alkali.
• Calcium hydroxide in solid form is known as 'slaked lime'. It neutralises acidic soil
• Calcium oxide and calcium carbonate are used to neutralise acidic gas.

  SO2 + CaO --> CaSO3

  SO2 + CaCO3 --> CaSO3 + CO2
• Barium sulphate is eaten as part of a 'barium meal'. It is good at absorbing x-ray and so it is used to outline the gut for x-rays.

  Although barium ions are toxic, this technique is harmless because barium sulphate is insoluble so it isn't absorbed by the blood.