Group 4

• Group IV tetrachlorides


  All the elements in Group IV form tetrachlorides, XCI4
• Tetrachlorides


  • Simple covalent molecules with tetrahedral structure
  • Volatile liquids with low boiling points
  • Non-polar because the dipoles cancel
• There is no simple pattern in the boiling points of the tetrachlorides
• Group IV tetrachlorides


  Compounds formed by Group IV elements (C, Si, Ge, Sn, Pb) with four halogen atoms
• Reactivity of the Group IV tetrachlorides with water


  1. All the tetrahalides, except CCl4, are readily hydrolysed by water to the oxide in the +4 oxidation state

  2. Acidic fumes of hydrogen chloride are also produced
• Hydrolysis reaction of tetrachlorides


  • SiCl4(l) + 2H2O(l) → SiO2(s) + 4HCl(g)
  • GeCl4(l) + 2H2O(l) ⇌ GeO2(s) + 4HCl(g)
• Hydrolysis of the Group IV tetrachlorides

  • The hydrolysis is reversible for the heavier tetrachlorides
  • The case of hydrolysis increases down the group from SiCl4 to PbCl4 as the metallic nature of the Group IV atom increases
  • When lead(IV) chloride is hydrolysed, a little decomposition of the lead(IV) chloride to lead(II) chloride also occurs
• Group IV elements


  • C, Si and Ge have giant covalent structures; Sn and Pb are metals
  • Down Group IV, the elements show a general decrease in melting point and a general increase in metallic character and electrical conductivity
  • Group IV elements form covalently bonded tetrachlorides
• The Group IV tetrachlorides are hydrolysed rapidly by water with the exception of carbon tetrachloride
• Oxides, apart from CO and CO2


  • Solids with giant structures and high melting points
• CO and CO2

  • Gases at room temperature, because they have a simple molecular structure with only weak forces between their molecules in the solid and liquid states
• Carbon monoxide, CO


  Has a strong triple bond and does not decompose on heating
• Germanium(II) oxide disproportionation


  2GeO(s) → GeO2(s) + Ge(s)
• Oxidation numbers of Germanium(II) oxide: +2, +4, 0
• Tin(II) oxide, SnO, and lead(II) oxide, PbO


  • Do not decompose on heating in the absence of air, readily oxidised to higher oxides in the presence of oxygen
• Carbon dioxide, CO2


  Has strong double bonds and does not decompose on heating
• The oxides in the +4 oxidation state


  Tend to decrease in stability down the group, except lead(IV) oxide, PbO2, which undergoes significant thermal decomposition
• Thermal decomposition of lead(IV) oxide

  PbO2(s) → PbO(s) + O(g)
• Acid-base properties of oxides

  • CO - very weakly acidic
  • CO2 - acidic
  • SiO - very weakly acidic
  • SiO2 - amphoteric
  • GeO - amphoteric
  • GeO2 - amphoteric
  • SnO - amphoteric
  • SnO2 - amphoteric
  • PbO - amphoteric
  • PbO2 - amphoteric
• The oxides in the +2 oxidation state


  Are less acidic (more basic) than the corresponding oxides in the +4 oxidation state
• CO2 reaction with water


  CO2(g) + H2O →<— HCO3(aq) + H+(aq)
• CO2 reaction with dilute alkalis


  CO2(g) + 2NaOH(aq) → Na2CO3(aq) + H2O
• The oxides in both oxidation states


  Become more basic down the group as the metallic character of the Group IV atom increases
• Reactions of carbon dioxide and silicon dioxide with alkalis


  • CO2 reacts with aqueous alkalis (hydroxide ions)
  • SiO2 only reacts with hot concentrated alkali
• SiO2 reaction with hot concentrated alkali

  SiO2(s) + 2NaOH(aq) → Na2SiO3(aq) + H2O
• Amphoteric oxides of Group IV


  • GeO2, SnO and PbO are all amphoteric, but have increasingly basic character in the order GeO2 < SnO < PbO
  • They all react with acids to form a salt with oxidation state +2
  • They all react with alkalis to form ions with oxidation state +2
• Amphoteric oxides of Group IV (oxidation state +2) reaction with acids

  SnO(s) + 2HCl(aq) → SnCl2(aq) + H2O
• Amphoteric oxides of Group IV (oxidation state +2) reaction with alkalis


  1. GeO(s) + 2OH-(aq) → GeO2-(aq) + H2O

  2. SnO(s) + 2OH-(aq) → SnO2-(aq) + H2O

  3. PbO(s) + 2OH-(aq) → PbO2-(aq) + H2O
• Amphoteric oxides of Group IV (oxidation state +4)


  • GeO2, SnO2 and PbO2 are all amphoteric
  • They all react with acids to form a salt with oxidation state +4
  • They all react with alkalis to form ions with oxidation state +4
• Amphoteric oxides of Group IV (oxidation state +4) reaction with acids


  SnO2(s) + 4HCl(aq) → SnCl4(aq) + 2H2O
• The relative stability of Group IV oxides in oxidation state +4

  Decreases down the group
• The acidic character of the Group IV oxides in oxidation state +2 and +4


  Decreases down the group and the basic character increases
• Group IV oxides in oxidation state +2 are more basic than the corresponding oxides in oxidation state +4
• Carbon monoxide


  This gas is prepared in the laboratory by using warm concentrated sulphuric acid to dehydrate methanoic acid
• Carbon monoxide


  • Burns with a pale blue flame
  • Forms carbon dioxide: 2CO(g) + O2(g) → 2CO2(g)
• Carbon monoxide's most notorious characteristic

  Ability to bind tightly to haemoglobin in the blood, preventing haemoglobin from carrying oxygen around the body
• Carbon monoxide gas forms as the result of incomplete combustion in petrol engines, and also in poorly ventilated gas fires, causing preventable deaths
• Oxide character


  As a general rule, the metalloids are usually basic, although some can vary from non-metal to metal-like as the group is descended, becoming less acidic (i.e. more basic) as the atomic number increases
• Carbon dioxide can dissolve in water to form a slightly acidic solution (pH=5)
• Reaction of carbon dioxide in water

  1. CO2(g) + H2O → H2CO3(aq)

  2. H2CO3(aq) + H2O → HCO3-(aq) + H3O+