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3.4

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  • 1. Group IV Elements
    • Section 3.4: Discuss the trends in
    • Bonding
    • Acid/ Base Character
    • Thermal stability of the oxides of oxidation states II and IV
  • 2. The Group IV Elements
    • Carbon – Silicon – Germanium – Tin - Lead
    • All elements in this group has 4 valent electrons
    • However, as atomic number increases along this group there is a considerable change in character of the elements.
    • Si
    C Ge Sn Pb
  • 3. (i) Bonding
    • We are all familiar with the fact that C is a non-metal and Pb is a metal.
    • The metallic (electropositive) character of the elements increase as atomic number increases.
    • The non-metallic (electronegative) character decreases as atomic number increases along group 4.
  • 4.
    • Carbon and silicon are non metals
    • Germanium is a metalloid, i.e. has an intermediate character.
    • Tin and lead show typical metallic properties.
    • Carbon, silicon and germanium are giant molecular structures
    • Tin and lead are metallic structures.
  • 5.
    • C, Si, Ge: forms covalent compounds with other elements, usually 4-valent.
    • Sn: covalent +4 and ionic +2 states are formed with almost equal ease
    • Pb: forms mainly ionic compounds in it +2 state and covalent compound sin its +4 state
  • 6. (ii) Acid/Base Nature
    • As you go down group 4 of the periodic table, the acidity of the oxides decrease with increasing atomic number.
    • The oxides of the elements are acidic. Towards the bottom of the group, the oxides become more basic, but never loses their acidity.
    • They are therefore said to be amphoteric.
  • 7.
    • Most elements in group 4 are able to form either a +2 ion or a +4 ion.
    • The oxides of oxidation state II are monoxides while those of oxidation states IV are dioxides.
  • 8.
    • Carbon Monoxide, CO
    • - slightly acidic
    • - does not react with water but will react with hot conc’n NaOH to give a solution HCOONa.
    • NaOH + CO HCOONa
    • No oxide of oxidation state II exist for silicon.
  • 9.
    • Carbon and Silica Dioxide CO 2 , SO 2
    • - weakly acidic
    • CO 2 reacts with water to produce H+ ions and a HCO 3
    • H2O (l) + CO 2(g) H + (aq) + HCO 3 - (aq)
    • The position of eq’brm is well to the left hand side .
  • 10.
    • CO 2 reacts with the base NaOH in the cold to give either sodium carbonate or hydrocarbonate (depending on the proportions)
    • 2NaOH + CO 2 Na 2 CO 3 + H 2 O
    • NaOH + CO 2 NaHCO 3
  • 11.
    • SO 2 does not react with water, since it is difficult to break up its covalent structure.
    • SO 2 reacts with hot, concentrated NaOH solution. Sodium silicate solution is formed.
    • 2NaOH + SiO 2 Na 2 SiO 3 + H 2 O
  • 12.
    • Monoxides of Ge, Sn and Pb
    • - all amphoteric, they show both basic and acidic properties.
    • - Basic Nature of the oxides
    • These oxides react to form salts
    • E.g. Rxn with concentrated HCl
    • XO (s) + 2HCl (aq) XCl (aq) + H2O (l) , where X can be Ge, Sn or Pb.
  • 13.
    • Lead (II) chloride is fairly insoluble in water and instead of getting a solution, it would form an insoluble layer over the lead (II) oxide, if you were using dilute HCl – stopping the rxn from going on.
    • The large excess of Cl - ions in the conc’n acid react with the PbCl 2 to produce soluble complexes such as PbCl 4 2-
    • PbCl 2 (s) + 2Cl - (aq) PbCl 4 2- (aq)
  • 14.
    • - Acidic Nature of Monoxides
    • The monoxides of Ge, Sn and Pb all react with bases like NaOH.
    • XO (s) + 2OH - aq) XO 2 2- (aq) + H 2 O (l)
  • 15.
    • Dioxides of Ge, Sn and Pb
    • - amphoteric
    • Basic Nature of the Dioxides
    • The dioxides react with the conc. HCl first to give compounds of the type XCl 4
    • XO 2 + 4HCl XCl 4 + 2H 2 O
  • 16.
    • They even react with excess Cl - ions in the HCl to give complexes such as XCl 6 2-
    • XCl 4 + 2Cl - XCl 6 2-
    • PbO 2 reacts with cold HCl. In hot or warm HCl, the lead (IV) chloride decomposes to give lead (II) chloride and chlorine gas.
  • 17.
    • Acidic Nature of the Dioxides
    • The dioxides react with hot conc. NaOH solution to give soluble complexes of the form [X(OH)6]2-
    • XO 2(s) + 2OH - (aq) + 2H 2 O (l) [X(OH) 6 ] 2-
  • 18.
    • Summary
    • CO 2 : dissolves in water to form a weak acid
    • CO : reacts with molen NaOH sodium methanoate
    • SiO 2 : reacts with a molten base a silicate
    • SnO 2 / SnO : react with dilute acid Sn4+ and Sn2+ salts and react with a molten base or conc aq. alkali to form a stannate (IV) or a stannate (II)
    • PbO 2 /PbO : react with dilute acids Pb (IV) compounds and Pb2+ salts and with a molten base or conc aq. alkali to form a plumbate (IV) or a plumbate (II). PbO is more basic than PbO 2 .
    • Pg 425 Ramsden
  • 19. (iii) Thermal Stability of the Oxides
    • First it is important to acknowledge that the oxides of oxidation state IV is more stable than those of oxd’n state II at the top of the group.
    • As atomic number increase going down the group, +2 oxd’n state becomes more stable than the +4 oxd’n state.