Carbon Family : Chemical properties

Chemical properties of Carbon Family

(1)     Hydrides : All the elements of group 14 combine with hydrogen directly or indirectly to form the covalent hydrides, MH4 (M = C, Si, Ge, Sn or Pb). The number of hydrides and the ease of preparation decrease on going from carbon to lead.  

The hydrides of silicon are called silanes having the general formula SinH2n+2. The hydrides of germanium are called germanes while those of tin are called the stannanes. Only lead forms an unstable hydride of the formula, PbH4 called the plumbane.

Three hydrides of germanium, i.e., GeH4, Ge2H6 and Ge3H8 and only two hydrides of tin i.e., SnH4 and Sn2H6 are well known. 

(2)     Oxides : Carbon forms five oxides CO, CO2, C3O2 (carbon suboxide), C5O2 and C12O9, C3O2 is the anhydride of malonic acid and CO2 is the anhydride of H2CO3 (carbonic acid) CO2 is a non-polar linear molecule due to maximum tendency of C to form pp–pp multiple bond with oxygen. Si forms SiO2. Pb forms a number of oxides. PbO can be obtained by heating

Pb(NO3)2, 2Pb(NO3)2 \underrightarrow { \quad Heat\quad } 2PbO + 4NO2 + O2.         

The red form of PbO is called litharge and the yellow form is massicot. Pb3O4 (Red lead, or Sindur) is prepared by heating litharge in air at 470°C, 6PbO + O2 \underrightarrow { \quad 47{ 0 }^{ 0 }C\quad }  2Pb3O4, Pb3O4 is a mixed oxide of PbO2. 2PbO. Pb2O3 is called lead sesquioxide.  GeO2, SnO2 etc. are also network solids. 

Note : SiO2, GeO2, SnO2 and PbO2 are all solids.

CO2 and SiO2 is acidic, GeO2 is weakly acidic while SnO2 and PbO2 are amphoteric in nature.

All the elements of group 14 except silicon from monoxides e.g., CO, GeO, SnO and PbO. Out of these monoxides only CO is neutral, while all other monoxides are basic.

(3)     Halides : Elements of group 14 react with halogens directly to form tetrahedral and covalent halides except C where its halide is produced by the action of halogens on hydrocarbons.   and PBI4 do not exist because Pb4+ is a strong oxidant and Brand I are strong reductants. Hence Pb4+ ion is difficult to survive in presence of strong reductants Brand I and is immediately reduced toPb2+.

 

Anomalous behaviour of Carbon

Carbon is found to differ in many properties from the rest of the members of group 14. This is because of the following : (i) Its smallest size (ii) Its high electronegativity (iii) Its property to catenate (iv) Absence of d-orbitals in it.

Some of the properties in which it differs from other members are,

(1)     The melting and boiling points of carbon are very high as compared to the rest to the members of the family.

(2)     Carbon in its diamond form is one of the hardest substance known.

(3)     It has maximum tendency to show catenation.

(4)     Carbon has high tendency to form Pπ – Pπ multiple bonds with other elements like nitrogen, oxygen, sulphur etc. Other members of the family form Pπ – dπ bonds and that also to a lesser extent.

(5)     CO2 is a gas while the dioxides of all other members are solids.

(6)     Carbon shows a maximum covalency of four while other members of the family may expand their covalency to six e.g., [SiCl6]2–, [PbCl6]2– etc.

(7)     Carbon is not affected by alkalies whereas other members react on fusion. For example, silicon form silicates,

Si + 2NaOH + ½ O2 → Na2SiO3 + H2.

                                    Sodium silicate