Physical Properties of Group IV Elements

Physical Properties of Group IV Elements

  1. The atomic radii increases down the group as the elements gain extra energy levels. The increased shielding effect of the full inner shells more than outweighs the increased nuclear charge and so the outer electrons are attracted less strongly.
  2. Ionic radii increases down the group. Ions are much smaller than atoms because they have lost the outer energy level and the nuclear charge is attracting four fewer electrons.
  3. Ionisation energies decrease down the group as the outer electrons become further from the nucleus and more highly shielded from the inner shells.

The Inert-pair effect

Each element has four outer electrons ns2 np2. The shielding of the outer shell for C and Si is quite efficient.

However, as we descend the group due to the presence of d and f electrons, which offer poor shielding, the outer s electrons are withdrawn into the atomic core and begin to behave as inner electrons.

Hence, Pb and Sn often behave as if they only have two outer electrons and show valencies of +2 and +4.

Structure of the elements

C, Si, Ge are all giant covalent, Sn and Pb are metallic.

This trend reflects the decreased ionisation energies and the increasing importance of the inert-pair effect.

Properties related to structure

  1. Melting and boiling points all decrease as we descend the group. There is a dramatic decrease after Ge which reflects this change in structure.
  2. Density and conductivity increase down the group reflecting the increasing metallic character.
  3. Electronegativity drops dramatically between C and Si due to the increased shielding effect and weaker attraction for the outer bonding electrons. There is little decrease after this due to the ineffectiveness of d and f electrons in shielding.

There are two stable oxidation states in Group IV, +2 and +4.

The relative stabilities of the oxidation states varies within the group as shown in the following graph.

Physical Properties of Group IV Elements

+4 Oxidation State

a) All elements have four outer electrons and so the main oxidation state for most elements is +4. The bonding in most compounds is covalent as too much energy would be needed to form M4+ ion.

Only PbF4 and SnF4 are truly ionic. Most compounds have a tetrahedral arrangement around the metal.

b) +4 is the most stable state for C, Si, Ge and Sn but is the least stable for Pb. Compounds of Pb(IV) are easily reduced to Pb(II) and are strong oxidising agents.

For example: PbO2(s) + 4HCl(aq) → PbCl2(s) + 2H20(l) + Cl2(g)

+2 Oxidation State

In this oxidation state only the p electrons are used in bonding and the s electrons exhibit the inert-pair effect. It is most unstable for C and Si but is most stable for Pb.

Compounds of both Pb(II) and Sn(II) are common and the bonding in them ionic. Compounds of C(II), Si(II), Ge(II) and Sn(II) are easily oxidised and are therefore strong reducing agents.

For example: 2CO(g) + O2(g) → 2CO2(g)

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