24.3 Group IV Oxides
Introduction to Group IV oxides
- Group IV elements form two types of oxides: monoxide and dioxide. This is because the elements have two possible oxidation states, +2 and +4.
- Monoxides include:
- carbon monoxide, CO
- silicon monoxide/silicon(II) oxide, SiO
- germanium monoxide, GeO
- tin(II) oxide, SnO
- lead(II) oxide, PbO
- Dioxides include:
- carbon dioxide, CO2
- silicon dioxide/silicon(IV) oxide, SiO2
- germanium dioxide, GeO2
- tin(IV) oxide, SnO2
- lead(IV) oxide, PbO2
- Carbon monoxide and carbon dioxide is a simple covalent molecule which exists as a gas at room temperature.
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- Silicon monoxide and silicon dioxide has a giant covalent structure(for more details, refer to Chapter 5).
- The difference in structure between carbon dioxide and silicon dioxide is due to silicon atom being larger. When the atom is larger, the overlapping of p orbitals to form a π bond is less complete and a π bond as such is very unstable. So, silicon bonded with the oxygen atoms in such a way that π bonds are not formed.
- Germanium monoxide and germanium dioxide have the same structure as silicon monoxide and silicon dioxide respectively
- Tin(II) oxide and tin(IV) oxide have a giant ionic lattice structure with ionic bonds between the Sn²⁺/Sn⁴⁺ and O²⁻.
- Lead(II) oxide and lead(IV) oxide have a giant ionic lattice structure with ionic bonds between the Pb²⁺/Pb⁴⁺ and O²⁻.
Group IV monoxides
- Carbon monoxide is a slightly acidic oxide which is only slightly soluble in It reacts with hot and concentrated sodium hydroxide, NaOH to give a solution of sodium methanoate.
CO + NaOH → HCOONa -
- Germanium, tin and lead monoxides are amphoteric oxides. They can act as an acid as well as a base.
- As a base : XO + 2HCl → XCl2 + H2O ; where X = Ge/Sn/Pb
- As an acid : XO + 2NaOH → Na2XO2 + H2O ; where X = Ge/Sn/Pb
Group IV dioxides
- Carbon dioxide is a slight acidic oxide which is only slightly soluble in It reacts with cold sodium hydroxide, NaOH to give either sodium carbonate or sodium hydrogencarbonate solution, depending on the proportion.
CO2 + 2NaOH → Na2CO3 + H2O or
CO2 + NaOH → NaHCO3
- Silicon dioxide is weakly acidic. It reacts with hot and concentrated sodium hydroxide to give sodium silicate. However, it does not react with water due to the strong covalent bonds need to be broken
SiO2 + 2NaOH → Na2SiO3 + H2O -
- Germanium, tin and lead dioxides are amphoteric oxides. They can act as an acid as well as a base.
- As a base : XO2 + 4HCl → XCl4 + 2H2O ; where X = Ge/Sn/Pb For germanium and tin dioxides, hot and concentrated hydrochloric acid is used. However, for lead dioxide, cold hydrochloric acid is used. This is because lead dioxide will decompose if the temperature increases
- As an acid : XO2 + 2NaOH → Na2XO3 + H2O ; where X = Ge/Sn/Pb
For all reactions, hot and concentrated sodium hydroxide is used.
Thermal stability of Group IV oxides
- Carbon, silicon and germanium oxides will disproportionate on heating.
2XO → X + XO2 ; where X = C/Si/Ge
- Tin and lead monoxide are stable on heating.
- This reflects the stability of +2 oxidation state of Group IV elements increases down the Group
- All dioxides are stable on heating except lead dioxide(lead(IV) oxide). This decomposes on heating to give lead(II) oxide and oxygen
2PbO2 → 2PbO + O2
- This shows the stability of +4 oxidation state of Group IV elements decreases down the Group