Group 2 - the alkaline earth metals

• trends in group 2: chemical trends

  -2 e- in their outermost shell

  -form ionic compounds

  -donate two outermost so act as reducing agents

  -going down metals become more reactive
• trends in group 2: ionisation energies

  -1st and 2nd IE decrease down group

  -though nuclear charge increase down, increased shielding and increased atomic radius outweigh

  -more reactive as you go down as it gets easier to remove 2 outer electrons
• trends in group 2: physical trends

  -going down elements become larger

  -melting point decreases as outer e- get further away from nucleus

  -attraction between nucleus and bonding e- decreases

  -density decreases then increases again after Ca
• group 2 hydroxides

  -going down solutions formed of group 2 oxides with water becomes more alkaline

  -when oxides are dissolved in water -->

  O2-(aq) + H2O(l) ----> 2OH-(aq)

  -higher conc of OH- more alkaline soln

  
  

  least Mg(OH)2

  Ca(OH)2

  Sr(OH)2

  most Ba(OH)2
• Group 2 sulphates

  -solubility of sulphates decreases going down group

  
  

  most MgSO4

  CaSO4

  SrSO4

  least BaSO4
• reactions of group 2: Be

  oxygen - reluctant to burn, white flame

  water - no reaction
• reactions of group 2: Mg

  oxygen - burns easily, bright white flame

  water - vigorous reaction with steam no reaction with cold
• reactions of group 2: Ca

  oxygen - difficult to ignite, red flame

  water - reacts moderately, hydroxide formed
• reactions of group 2: Sr

  oxygen - difficult to ignite, red flame

  water - reacts rapidly, hydroxide formed
• reactions of group 2: Ba

  oxygen - difficult to ignite, green flame

  water - reacts vigorously, hydroxide formed
• group 2 and water

  M(s) + 2H2O(l) -> M(OH)2(s) + H2(g)
• group 2 and acid

  -form colourless solutions of metal salts

  -dilute HCl - M (s) + 2HCl (aq) → MCl2 (aq) + H2 (g)

  -d. H2SO4 - M (s) + H2SO4 (aq) → MSO4 (aq) + H2 (g)
• group 2 oxides and water: BeO

  BeO(s) + H2O(l) ---> Be(OH)2(aq)
• group 2 oxides and water: MgO

  MgO(s) + H2O(l) ---> Mg(OH)2(aq)

  -MgO is only slightly soluble therefore a weakly alkaline soln is formed pH10
• group 2 oxides and water: CaO

  CaO(s) + H2O(l) ---> Ca(OH)2(aq)

  -vigorous reaction releases lots of energy which causes some water to boil off as the CaO solid lumo seems to expand and crack open pH11
• group 2 oxides and water: SrO

  SrO(s) + H2O(l) ---> Sr(OH)2(aq)
• group 2 oxides and water: BaO

  BaO(s) + H2O(l) ---> Ba(OH)2(aq)
• uses of group 2 elements

  -commonly used in agriculture

  -limestone - impure CaCo3

  -quicklime - CaO, formed by thermal decom of CaCO3

  -slaked lime - Ca(OH)2 formed when water added to quicklime

  -used to raise pH of soil

  -CaCO3 more commonly used because cheaper and safer to handle
• solubility of hydroxides

  -solubilities mean that compounds have different uses

  -solubility increases down the group

  -Mg(OH)2 is least soluble

  -Ba(OH)2 is the most soluble
• Magnesium Hydroxide uses

  -Mg(OH)2 is the least soluble

  -can be used as antacid as it is alkaline and neutralise acids

  -can be similarly used in agriculture to neutralise acidic soils
• solubility of sulfates

  -solubility decreases down group

  -MgSO4 is the most soluble

  -BaSO4 is the least soluble
• Barium Sulfate uses

  -its insolubility means its useful in medicine as barium meals

  -barium meals are a form of medical tracer that allows internal tissues and organs to be imaged

  -BaSO4 is toxic if it enters the blood stream but because its insoluble, it cannot be absorbed - therefore safe to use
• Metal Extraction

  -magnesium is used in extraction of titanium from titanium chloride via displacement reaction

  TiCl4 + 2Mg -------> 2MgCl2 + Ti
• Reactivity of group 2

  -increased shielding down group makes outer electrons easier to lose

  -reactivity increases down group
• melting points of group 2

  -elements are metallic meaning the larger the ion, the weaker the attractive force as the force has to act over a greater distance

  -melting point decreases down group