Inorganic Chemistry: Group 2

TRENDS
1. Ionisation Energy
  1. Nuclear charge increases → force of attraction for the e- being removed increases → increase in IE down group
  2. Each added quantum shell → energy of outermost e- increases
  3. Number of filled inner shells increases → force of repulsion on e- being removed increases → decrease in IE down group
  4. Combined effect of the last 2 factors outweighs the effect of 1st factor → decrease in IE down group
2. Reactivity
  1. Reactivity of G2 metals increases down group
  2. Atomic radii increases → more shielding → nuclear attraction decreases → easier to remove outer e-
3. Melting points
  1. Melting points decrease down the group
  2. Metallic bonding weakens as atomic size increases → distance between cations + delocalised e- increases → electrostatic attractive forces between cations + delocalised e- weaken
4. Atomic Radius
  1. Atomic Radius increases down the group
  2. More e- → more shells of e- → bigger atom
REACTIONS
1. With Oxygen
  1. Group 2 metals burn in oxygen
  2. Magnesium burns with a bright white flame + formation of white solid
  3. GE: 2M(s) + O2(g) → 2MO(s)
2. With Chlorine
  1. Group 2 metals combine with chlorine when heated in the gas
  2. GE: M(s) + Cl2(g) → MCl2(s)
3. With Water
  1. Magnesium reacts slowly with water + doesn't completely react
  2. Calcium, Strontium & Barium react w increasing vigour → increase in effervescence
  3. GE: M(s) + 2H2O(l) → M(OH)2(aq) + H2(g)
  4. Reaction with Calcium (Calcium Hydroxide is only slightly soluble in water, so liquid turns cloudy: Ca(s) + 2H2O(l) → Ca(OH)2(s) + H2(g)
4. Magnesium & Steam
  1. When heated in steam, Magnesium Oxide is formed (white solid) and Hydrogen gas in a vigorous reaction
    1. Mg(s) + H2O(g) → MgO(s) + H2(g)
REACTIONS OF GROUP 2 OXIDES & HYDROXIDES, & TRENDS IN SOLUBILITY
THERMAL STABILITY OF GROUP 2 COMPOUNDS & THE COMPARISON WITH GROUP 1
1. Carbonates
  1. G2 carbonates decompose on heating → produce G2 oxides + CO2 gas
    1. More thermally stable as you go down the group → bigger cations → less of a polarising effect → distort carbonate ion less → C–O bond is less weakened → doesn't break down easily
    2. EXP: Heat known mass of carbonate in boiling tube + pass gas produced through lime water
    3. MgCO3(s) → MgO(s) + CO2(g)
  2. G1 carbonates do not decompose apart from Lithium
    1. Only have +1 charges → don't have a big enough charge density to polarise the carbonate ion
    2. Li → small enough to have polarising effect
    3. Li2CO3(s) → Li2O(s) + CO2(g)
2. Nitrates
  1. G2 nitrates decompose on heating to produce G2 oxides, O2 gas and NO2 gas
    1. Observe brown gas evolving (NO2) + white nitrate solid melt to colourless solution, then resolidify
    2. More thermally stable as you down the group → bigger cations → less of a polarising effect → distort carbonate ion less → N–O bond is less weakened → doesn't break down easily
    3. Mg(NO3) decomposes the easiest → Mg2+ ion is smallest + has greater charge density → causes more polarisation of nitrate anion → weakens N–O bond
    4. 2Mg(NO3)2 → 2MgO + 4NO2 +O2
  2. G1 nitrates do not decompose in the same way as G2 (apart from Lithium nitrate) → decompose to give nitrate (III) salt + O2 gas
    1. 2NaNO3 → 2NaNO2 + O2
FLAME TESTS & THE TEST FOR AMMONIUM IONS
1. RED: Lithium, Calcium, Rubidium
2. YELLOW: Sodium
3. LILAC: Potassium
4. BLUE: Caesium
5. GREEN: Barium
6. Heat causes an electron to move to higher energy level → e- is unstable at higher e- level → drop back down → energy is emitted in form of visible light energy → with wavelength of observable light

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Inorganic Chemistry: Group 2

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