group 2

• group 2 metals are alkaline earth metals in the S block with 2 electrons in their outer shell
• atomic radii increases down the group as going down the atoms have more shells of electrons making the atom bigger and more shielding so metallic bonding is weaker
• Melting points decrease down the group as the atomic size increases so the distance between the positive ions and delocalized sea of electrons increases. Therefore the metallic bonding is weaker as electrostatic attraction between oppositely charged forces weaken

  
  

  amount of energy to break bonds decreases so melting point decreases
• group 2 physical properties:

  • relatively high mp + bp but decrease down a group
  • low density (denser than group 1 tho)
  • when they react they form white compounds

  [only D block forms coloured compounds]
• REACTIVITY OF GROUP 2 METALS

  reactivity of group 2 metals increases as you go down a group

  • the atom getting larger so therefore more shielding and larger distance between the negative outer electron and positive nucleus
  • atomic radii increases and electrons are held less tightly on its outer shell

  therefore the effect of the nuclear charge is reduced making it easier to loose 2 electrons on its outer shell in order to become stable and form 2+ ions
• first ionisation energy is always lower than second ionisation energy:

  • as the outermost electrons are held more weakly because they are successively further from the nucleus in additional shells
  • and are more shielded from the attraction of the nucleus by the repulsive force of inner shell electrons.
• second ionisation energy is also higher than the first as once first ionisation energy has happened there is now more protons compared to electrons so atomic radii is smaller due to the increased effect of nuclear charge
• ionisation energy decreases going down the group cause:

  • more electron shells are added as you move down Group 2 which means the atomic radius increases and therefore the outermost shell becomes further away from the positive nucleus.
  • more shielding reducing the effect on nuclear charge so less nuclear attraction
• Group 2 elements are reducing agents as they reduce [GAIN ELECTRONS] other species whilst be oxidised [LOSE ELECTRONS]
• Reaction G2 with cooler water: slower

  • Magnesium + Water ---> Magnesium Hydroxide + hydrogen gas

  Mg + 2 H2O ---> Mg(OH)2 + H2

  0 +1 +2 0

  Mg looses 2 electrons so is oxidised
• Reaction G2 with steam/ hot water: rapid

  • Magnesium + Water ---> Magnesium oxide + hydrogen gas

  Mg(s) + H2O(g) --->MgO(s) + H2 (g)

  Mg appears as a white powder
• group 2 reactions observations

  • fizzing, (more vigorous down group)
  • the metal dissolving (faster down group)
  • the solution heating up (more down group)
  • with calcium a white precipitate appearing (less precipitate forms down group with other metals)
• HYDROXIDES

  Solubility ​increases down group​ 2 meaning magnesium hydroxide - (Mg(OH)​2​ ) is the least soluble or sparingly soluble and barium hydroxide (Ba(OH)​2​ ) the most soluble.
• SULFATES

  Solubility ​increases down group​ 2 meaning magnesium sulfate (MgSO4) is the most soluble and barium sulfate (BaSO4​ ) the least soluble.
• ionic equation of magnesium hydroxide:

  • 2OH- (aq) + Mg+2 (aq) ----> Mg(OH)2 (s)

  white precipitate
• testing for sulfates:

  1. add BaCl2 (aq) acidified with dilute HCl to solution you are testing
  2. If sulfate ions are present a white precipitate of BaSO4 (s)/ barium sulphate will be formed

  Ba 2+ (aq) + SO4 2- (aq) ----> BaSO4 (s)
• USES:

  Mg(OH)2 is used as an antacid in medicine for indigestion by neutralising excess stomach acid
• USES:

  Ca(OH)2 is used in agriculture to neutralise acidic soils by raising the pH of farm soils
• USES: Barium meals

  • BaSO4 is used in barium meals as a patient drinks suspension containing the barium sulfate so when x-rayed the barium absorbs the rays to see structure of soft tissues and organs like intestines

  normally barium compounds are toxic but BaSO4 has very low solubility so it doesn't get absorbed into the blood
• USES: Mg as a reducing agent when extracting titanium

  1. Titanium oxide converted to titanium chloride (TiCl4) by heating it with carbon in a stream of chlorine gas
  2. TiCl4 is then purified by fractional distilation before being reduced by Magnesium in a furnace at 1000 C

  TiCl4 (s) + 2Mg (l) ----> Ti (s) + 2 MgCl2 (l)
• TiCl4 (s)+ 2Mg (l) ----> Ti (s) + 2 MgCl2 (l)

  • Titanium is reduced = Ti 4+ + 4e ----> Ti
  • Magnesium is oxidised = 2Mg ----> 2Mg 2+ + 4e
• USES: CaO or CaCO3 in the removal of SO2 in flue gas desulfurisation

  • wet scrubbing react acidic sulfur dioxide with an alkali - a slurry of CaO/ CaCO3 with water is sprayed onto the flue gas to produce calcium sulfite

  
  

  SO2 + CaO ----> CaSO3

  SO2 + CaCO3 ----> CaSO3 + CO2
• removing sulfur dioxide from flue gas desulfurisation

  • CaO (s) + SO2 (g) ----> CaSO3 (s)
  • CaCO3 (s) + SO2 (g) ----> CaSO3 (s) + CO2 (g)