group 2

• what do all electron configurations have in common in G2?

  $S^2$

  increasing the energy level as you go down
• as you go down the group, atomic radius:

  • increases
  • higher atomic number = more electrons
  • further from nucleus
  • compared to to G1 atomic radius, G2 has smaller atomic radius, extra proton exerts a greater attraction on the electrons
• as you go down the group, ionic radius:

  • increases
  • ions are smaller than atoms - on removing the outer shell electrons, the remaining electrons are now in fewer shells
  • less electrons, less shielding, more nuclear attraction, pulls it in closer
• GENERALLY as you go down G2, melting point:

  • decreases
  • each atom contributes two electrons to the delocalised cloud
  • larger ions
  • electron cloud doesn't bind them as strongly
  • metallic bonding gets weaker
• melting point + Beryllium (Be): Be has covalent properties in bonding
• melting point + magnesium (Mg): doesn't fit the trend bc crystalline structure affects m.p of a metal
• G1 VS G2 melting point: G1 has lower m.p. than G2 because it only has one electron
• as you go down the group, first ionisation energy:

  • decreases
  • nuclear attraction force decreases
  • less energy required to remove an electron
  • atomic radius increases
• as you go down G2, reactivity:

  • increases
  • nuclear charge increases
  • but shielding increases
  • less nuclear attraction
  • less energy to remove electron (which will be reacting)
• qualitative analysis:

  Mg: white light

  Ca: orange-red

  Ba: apple-green

  Sr: red
• Mg + cold water -> Mg(OH)2 (aq) slow reaction
• Mg + steam -> MgO (s) quick reaction
• Ba + cold water = vigorously reacts
• chloride salts are aqueous and soluble
• barium + strontium will be insoluble
• chloride + sulfate salts are soluble
• G2 + HCl -> chloride salt (aq) + H2 (g)

  G2 + H2SO4 -> sulfate salt + H2 (g)

  aq: Mg, Ca

  s: Sr, Ba
• very dilute nitric acid: 2HNO3 + Mg = Mg(NO3)2 + H2. 
• dilute nitric acid: 3Mg + 8HNO3 -> 3Mg(NO3)2 + 2NO + 4H2O
• concentrated nitric acid: Mg +HNO3 -> Mg(NO3)2 + NO2 + H2O
• as you go down G2, oxides of G2 are:

  • more reactive
  • more soluble - because larger ions form weaker bonds with the OH- ion due to the smaller charge density so easily broken
  • more pH - because more OH- ions
• as you go down G2, hydroxides:

  • increase
  • because solubility increases
  • metal ions get larger so charge density decreases
  • lower attraction between OH- ions and larger 2+ ions
  • ions will spilt away from each other more easily
  • greater concentration of OH- in water
• as you go down G2, sulfates:

  • decrease
  • cation gets longer, it has a lower charge density
  • it becomes less attracted to the polar water molecules

  1. greater charge density
  2. more attracted to water
  3. ionic lattice breaks up more easily
  4. more soluble
• metal carbonate: as you go down, atomic radius increase, stronger force of attraction
• properties of metal carbonate:

  1. insoluble, more insoluble as you go down group
  2. ease of decomposition as you go down group
• driving force is formation of oxide. the smaller ion with its greater charge density holds onto the O2- ion to make a more stable compound