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Group II

Group II

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Page 1: Group II

Group II

Page 2: Group II

The focus for Inorganic Chemistry (Gp II, VII, Transition Elements) is the trends for the physical and

chemical properties of the elements.

Group II

Page 3: Group II

• Atomic radii• Ionisation Energy (IE)• Melting point/ boiling point (mp/ bp)

For each property, it is important to:(1) remember the trends(2) learn to explain for the trends

Physical Properties

Page 4: Group II

The key to explaining correctly for the trends is to remember the factors that affect each trend.

Physical Properties

Page 5: Group II

Physical Properties

Property

atomic/ ionic radii, IE, electro-vity

mp/bp, ∆Hfusion/∆Hvaporisation, conductivity, solubility

ease of decomposition, decomposition T

Factor

effective nuclear charge (nuclear charge + screening effect)

structure & bonding (lattice energy)

polarising power of cation

Page 6: Group II

- Gp II metals are strong reducing agents

Down the group- Tendency to be oxidised ↑- Reducing ability ↑- Reactivity ↑

Chemical Properties

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1. Rxn with OxygenM (s) + O2 (g) 2MO (s)

2. Rxn with WaterM (s) + H2O (l) M(OH)2 (aq) + H2 (g)

Exception: Mg (s) + H2O (g) MgO (s) + H2 (g)

3. Rxn of Oxides with WaterMO (s) + H2O (aq) M(OH)2 (aq)

Chemical Properties

Page 8: Group II

4. Thermal Decomposition

M(NO3)2 (s) → MO(s) + 2NO2(g) + ½O2(g)

MCO3 (s) → MO(s) + CO2(g)

M(OH)2 (s) → MO(s) + H2O(g)

Down the group, thermal stability It is important to memorise the general eqns!

Chemical Properties

Page 9: Group II

• Students often mix up the explanation for trends for melting point and decomposition temperatures.

• For ionic compounds, melting involves breaking of ‘intermolecular’ bonds while decomposition involves breaking ‘intramolecular’ bonds.

Physical Properties

Page 10: Group II

M2+

Melting breaks ionic bonds strength of ionic bond q+ q–

r+ + r–

Decompositionbreaks covalent bonds strength of covalent bond polarising power of M

Chemical Properties

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Solubility of Gp II…- carbonates/ sulfates decrease down Gp- hydroxides/ oxides increase down Gp

Solubility Trends

• For solubility trends, you only need to memorise the trends.

• The explanation for the trends is not straightforward and unlikely to be tested.

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Q: How can we experimentally determine the trend for the ease of decomposition of Gp II compounds?

Further Reading

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A: There are a few methods:

- Measure volume of gas collected after a fixed timei.e. the larger the volume of gas produced, the easier the compound decomposes.

- Measure the time taken to collect a fixed volume of gasi.e. the shorter the time taken, the easier the compound decomposes

Further Reading