Group IV

Allotrope of Carbon

Carbon has a number of allotropes:

• Graphite

• Diamond

• Fullerenes

Oxidation States

In carbon, silicon, germanium and tin are normally found in the +4 oxidation state whereas lead is more stable as the +2 oxidation state.

Why does the +2-oxidation state exist?

The fact that the +4 oxidation state exists is of no surprise as these elements are Group IV elements. This means that they have the electronic structure of ns²np_x¹ np_y¹ np_z⁰. If all of these electrons are lost the oxidation state would be +4.

As you get closer to the bottom of the Group, there is an increasing tendency for the s² pair not to be used in the bonding. This is often known as the inert pair effect, and is dominant in lead chemistry.

The inert pair effect comes in play with the p-block elements of the 4th, 5th and 6th period come after d-block elements, but the electrons present in the intervening d- (and f-) orbitals do not effectively shield the s-electrons of the valence shell. As a result, the inert pair of ns electrons remains more tightly held by the nucleus and hence participates less in bond formation.

When the total energy for the four ionisation energies is taken into consideration it is noted that there is an increase in energy between tin and lead, and this is mainly due to the inert pair effect of the 6s electrons. In the case of lead this means that it is much more difficult to remove the s electrons and thus it will only have the +2 oxidation state.

Sn (II) and Pb (IV)

Sn (II) and Pb (IV) do exist but seeing that these are not the most stable oxidation states Sn (II) is a good reducing agent whilst Pb (IV) is a good oxidising agent.

Oxides

CO: This is a covalent neutral compound.

CO₂: This is a covalent acidic compound.

SiO₂: This is a giant covalent acidic compound. As SiO₂ does not dissolve in water it only acts as an acid when it is reacted with an alkali, such as NaOH.

SiO₂ + 2NaOH –> Na₂SiO₃ + H₂O

SnO: This is an ionic amphoteric oxide.

SnO₂:_­ This is an ionic amphoteric oxide.

PbO: This is an ionic amphoteric oxide.

PbO₂: This is an ionic amphoteric oxide.

Hydrides

CH₄

Preparation

Al₄C₃ + H₂O –> 4Al₂O₃ + 3CH₄

CH₃COOH + NaOH –> CH₃COO^– Na⁺ –> CH₄

SiH₄

Preparation

Mg₂Si + 4HCl –> 2MgCl₂ + SiH₄

Chlorides

Preparation

All of the Grp (IV) can be prepared by direct combination apart from CCl₄.

CH₄ +4Cl₂ –> CCl₄ + 4HCl (Under UV)

Si + 2Cl₂ –> SiCl₄ (heat)

Sn + 2Cl₂ –> SnCl₄ (heat)

Pb + 2Cl₂ –> PbCl₄ (heat)

It must be noted that at room temperature PbCl₄ will decompose to form PbCl₂ and Cl₂

PbCl₄ –> PbCl₂ + Cl₂

SnCl₂ can be prepared via the displacement reaction between Sn and HCl.

Sn + 2HCl –> SnCl₂ + H₂

Reaction with water

Carbon tetrachloride does not react with water whilst all the other tetrachlorides react with water in order to create the dioxide.

SiCl₄ + 4H₂O –> Si(OH)₄ + 4HCl –> SiO₂ + 2H₂O

PbCl₄ + 4H₂O –> Pb(OH)₄ + 4HCl –> PbO₂ + 2H₂O

CCl₄ does not hydrolyse with water due to two main reasons:

1. Carbon is a very small atom whilst chlorines are quite bulky in size, therefore there is very little room from where the water can attack the carbon.
2. If the water were to attack the carbon there is a small timeframe where 10 electrons would need to be accommodated by the carbon atom and there is no place for these extra 2 electrons to go, as there are no d-orbital spaces available and therefore the reaction cannot take place.

SnCl₂ can partially hydrolyse in water to form a basic salt.

SnCl_2(aq) + H₂O_(l) ⇌ Sn(OH)Cl_(s) + HCl_(aq)

PbCl₂ is a completely ionic compound that is insoluble in water.