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

• 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

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

Physical Properties

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

- Gp II metals are strong reducing agents

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

Chemical Properties

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

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

• 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

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

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.

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

Further Reading

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