Elements of group IV A and V A compounds

To learn about periodic elements

1. UNIT -IV ELEMENTS OF GROUP IV-A AND V-A GROUP IV-A

2. GROUP DISCUSSION Carbon, silicon, germanium, tin and lead form IV-A group of the periodic table. Their inclusion in the same sub-group of the periodic table is justified by general characteristics of the elements and their compounds

3. Similarities and gradation in properties of the elements Electronic configuration Allotropy Metallic and non-metallic character Covalency Oxidation states Complex formation Catenation Action of caustic alkalies

4. Similarities and gradation in properties of the compounds Hydrides Oxides Halides Acids

5. COMPARISON OF CARBON AND SILICON Electronic configuration: Both carbon and silicon have 4 electrons in their valence shell.’ C=6=2,4 Si=14=2,8,4 Nature: Both the elements are non-metals Valency : Both are tetravalent Oxidation state: Both carbon C and Si show invariably an oxidation state of +4. Allotropy: Both carbon and silicon show allotropy i.e. they exist in more than one form. Nature of oxides: The oxides of C and Si viz. CO 2 and SiO 2 are acidic. Formation of hydrides: Both C and Si form a number of volatile hydrides which are covalent in nature. Examples, Formation of acids: Both form similar types of acids.

6. Points of difference Catenation Multiple bonds Reaction with alkalies Formation of lower oxides Nature of dioxide Reaction with halogens Hydrolysis of tetrahalides Stability of oxy-acids Stability of hydrides Formation of complex compounds

7. COMPOUND OF SILICON Carbonyl chloride (Phosgene) Preparation: Carbonyl chloride is formed when equal volumes of carbon monoxide and chlorine are exposed to sunlight or passed over activated charcoal. Properties Carbonyl chloride is readily decomposed by water giving CO 2 and HCl . COCl 2 reacts with ammonia to form urea Uses: It is a poisonous gas in warfare.

8. Silicon hydrides ( Silanes ) Silicon is less electronegative than hydrogen and forms a number of hydrides called silanes . These are similar to saturated hydrocarbons ( alkanes ) and have the general formula Si n H 2n+2 . Examples: Silico -methane or monosilane SiH 4 Silico -ethane or disilane Si 2 H 6 Preparation: Silanes are usually prepared by the action dil. HCl on magnesium silicide . Better yield is obtained by the action of ammonium bromide on magnesium silicide in liquid ammonia of ammonium bromide on magnesium silicide in liquid ammonia.

9. Properties Action of air: All the silanes are spontaneously inflammable in air. They burn in air forming SiO 2 and H 2 . Action of water: They are hydrolysed by water to form SiO 2 and H 2 . Reaction with alkali: Silanes react vigorously with alkalies forming silicates and hydrogen Reducing property: Silanes are strong reducing agents SiH 4 precipitates copper silicide when passed into a copper salt solution. When passed into a solution of silver nitrate, SiH 4 precipitates silver. Substitution reaction: Monosilane , like methane, reacts with chlorine and gives rise to chlorosilanes .

10. Silicates Classification and structure All silicates contain tetrahedralSiO 4 4- units. These units are linked in different manner. Classes of silicates: i ) Silicates with discrete anions ii) Silicates with extended anions iii) Silicates with three dimensional net work.

11. Silicates with discrete anions Silicates with simple discrete anions Contain individual tetrahedral (SiO 4 4- ) tetrahedron is shared with the neighbouring tetrahedra . Silicates with non-cyclic discrete anions One oxygen atom of each SiO 4 4- tetrahedral is shared with the neighbouring terahedra . Silicates with cyclic discrete anions Contain cyclic anions like Si 3 O 9 6- , Si 6 O 18 12- etc. Formed by sharing two oxygen atoms of each tetrahedron with the neighbouring tetrahedral

12. Silicates with extended anions Silicates with simple chain anions When each tetrahedron shares two oxygen atom Silicates with double chain anions Two paralled chains are held together by shared oxygen atoms giving rise to anions like (Si 4 O 11 ) n 6n- s with the neighbouring tetrahedral. Silicates with layer structure When each tetrahedron shares three oxygen atoms with the neighbouring tetrahedral, silicates with layer structure of composition of formed.

13. Silicates with three dimensional net work In this case, all the four oxygen atoms of each SiO 4 tetrahedron are shared with the neighbouring tetrahedral giving rise R to the composition (SiO 2 ) as shown below: Litharge ( PbO ) Preparation: Litharge is commercially obtained by heating lead in air to a temperature above its melting point. Uses : Litharge is a reddish yellow powder used. In the manufacture of plasters, varnishes, glazes, flint glass and enamels. In paint making and vulcanisation of rubber. In making storage batteries. In making red lead and ceramic cement (litharge + glycerine) to bind glass and metal.

14. Red lead (Pb 3 O 4 ) Preparation : It is prepared as bright red powdered by roasting litharge ( PbO ) in air at 450 C in am muffle furnace. Uses : Red lead is used As a red pigment in paints As a pipe joining cement in plumbing work In glass industry In match industry as oxidising agent In silvering of mirror

15. White lead Preparation: White lead (basic lead carbonate) is manufactured by Dutch process. Finely divided metallic lead is oxidised in the presence of acetic acid and moisture of form basic lead acetate.