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The Applications of the Core Principles of Chemistry

The periodic table ­ groups 2 and 7
Group 2
Ionisation energies
Trend in first ionisation energy
First ionisation energies decrease down the group
- More filled shells, so the outer electrons are more
shielded
- Radius of the atom increases, so…

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The Applications of the Core Principles of Chemistry
Oxides
Group 2 oxides and hydroxides are bases
- They react with acid to form salt and water
With water
BeO No reaction
MgO MgO + H2O Mg(OH)2 Slowly and incompletely
CaO CaO + H2O Ca(OH)2 Very exothermically
SrO SrO(s) + H2O(l)…

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The Applications of the Core Principles of Chemistry


Thermal stability trend
Thermal stability depends upon the polarising power of the cation, determined by charge density
- Larger charge + smaller radius = higher charge density
Compounds with cations that strongly polarise the anion are more easily decomposed
Ease of decomposition…

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The Applications of the Core Principles of Chemistry


Experiments
Flame tests
Group 1 Group 2 Origin
Lithium Calcium Produced by the movement of electrons in the
Sodium Strontium metal ions
Potassium Barium When heated, electrons gain energy and can jump
Rubidium into empty orbitals at higher levels
Caesium They then…

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The Applications of the Core Principles of Chemistry
Trends
First ionisation energy
Decrease down group
Nuclear charge increases, but number of shielding electrons increases by same amount
- Effective nuclear charge stays about the same
Atomic radius increases as new shells are added
- Outermost electrons become less strongly held…

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The Applications of the Core Principles of Chemistry
Reactions with alkali
Room temperature
Cl Cl2 + 2NaOH NaCl + NaOCl + H2O Disproportionation
0 -1 +1

Ionic: Cl2 + OH- Cl-1 + OCl+1 + H2O
Br
I

Hot alkali
Cl 3Cl2 + 6OH- 5Cl- + Cl3 + 3H2O Disproportionation
0…

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