Transition metals

• Transition elements --> the elements Ti - Cu as transition elements i.e. d-block elements that have an ion with an incomplete d-subshell
• • Scandium and zinc aren't transition elements as they have complete d-subshells
• • d-block elements are all metallic
  • Have high melting points & boiling points
  • Shiny in appearance
  • Conduct both electricity and heat
• Electron configuration of d-block ions:

  • When forming an atom, the 4s orbital fills before the 3d orbitals
  • When forming an ion, the 4s orbital empties before the 3d orbitals
• • Scandium only forms the ion SC3+ by loss of two 4s electron and one 3d electron
  • The elcetron configuration of Sc is 1s2 2s2 2p6 3s2 3p6 3d1 4s2
  • Sc3+ has an electronic configuration of 1s2 2s2 2p6 3s2 3p6
• • zinc only form the Zn2+ ion by the loss of its two two 4s electron
  • The elctron configuration of Zn is 1s2 2s2 2p6 3s2 3p6 3d10 4s2
  • Zn2+ has an electronic configuration of 1s2 2s2 2p6 3s2 3p6 3d10
• Complex ion —> metal ion with datively bonded ligands
• Ligand —> particle with lone pair of electrons that bonds to metals by a dative bond
• Coordination number –-> number of coordinate bonds from ligands to metal ions
• Monodentate --> H2O, Cl-, NH3
• Bidentate --> NH2CH2CH2NH2 ('en')
• • The overall charge on a complex ion is the sum of the charges on the central metal ion and any ligands present
• • Some ligands like water are neutral and have no charge, whereas other ligands like the hydroxide ion are negatively charged
• Monodentate ligands --> A ligand that is able to donate one pair of electrons to a central metal ion. E.g: water, ammonia
• Bidentate ligands --> Can donate 2 lone pairs of electrons to the central metal ion, forming 2 coordinate bonds
• • The shape of a complex ion depends upon its coordination number
  • Many complex ions have a coordination number of 6, giving an octahedral shape
  • Complexes with a coordination number of 4 have 2 common shapes - tetrahedral & square planar
• • A square planar shape occurs in complex ions of transition metals with 8 d-electrons in the highest energy d-subshell
  • In this shape, the ligands are arranged at the corners of a square, similar to the octahedral shape but without the ligands above & below the plane
• Isomerism:

  • Geometrical ( cis -trans ) isomerism
  • Square planar complexes of the form [MA2B2]^n+ exist in 2 forms

  
• • For complex ions, the type of stereoisomerism depends on the number & type of ligands that are attached to the central metal ion, and the shape of the complex
• • Optical isomerism only occurs in octahedral complexes containing 2 or more bidentate ligands
  • Optical isomers called enantiomers, are non-superimposable mirror images of each others
• Ligand substitution:

  • When one ligand replaces another
  • [Cu(H2O)6]2+ + 4NH3 <=> [Cu(NH3)4(H2O)2]2+ + 4H2O
• Haemoglobin --> A complex containing iron (II) which is responsible for the red colour in blood & for the trasport of oxygen by red blood cells
• • When copper(II) Sulfate is dissolved in water, the pale blue complex ion [Cu(H2O)6]^2+ is formed in aqueous solution
• • When an excess of aqueous ammonia is added to a solution containing [Cu(H2O)6]^2+ the pale blue solution changes colour to form a dark blue solution
  • [Cu(H2O)6]^2+ (aq) + 4NH3 (aq) —> [Cu(NH3)4(H2O)2]^2+ (aq) + 4H2O (l)
  • In the reaction, 4 ammonia ligands have replaced 4 of the water ligands
  • Both [Cu(H2O)6]^2+ (aq) & [Cu(NH3)4(H2O)2]^2+ (aq) are octahedral complex ions
• • When an excess of concentrated HCl is added to a solution containing [Cu(H2O)6]^2+, the pale blue solution changes colour to form a yellow solution
  • Example of ligand substitution, 6 water ligands have been replaced with 4 chloride ligands
  • [Cu(H2O)6]^2+ (aq) + 4 Cl- (aq). <==> [CuCl4]^2- (aq) + 6H2O (l)
  • Chloride ligands are larger in size than the water ligands, so fewer chloride ligands can fit round the central Cu2+ ion
• • When chromium (III) potassium Sulfate, KCr(SO4)2 . 12(H2O) = chrome alum, is dissolved in water the complex ion [Cr(H2O)6]3+ is formed = pale purple solution
  • When chromium (III) Sulfate is dissolved in water, a green solution containing chromium (III) is formed
• • [Cr(H2O)6]^3+takes part in a ligand substitution reaction with a excess of aqueous ammonia forming the complex ion [Cr(NH3)6]^3+
  • Initially a grey green precipitate of Cr(OH)3is formed
  • The Cr(OH)3 precipitate dissolves in excess ammonia to form the complex ion [Cr(H2O)6]^3+
  • [Cr(H2O)6]^3+ (aq) + 6NH3 (aq) —> [Cr(NH3)6]^3+ (aq) + 6H2O (l)
  • Violet —> purple
• precipitation reaction —> occurs when 2 aqueous solutions containing ions react together to form an insoluble ionic solid, called a precipitate
• Ion: Cu2+ with NaOH

  • Blue solution reacts to form a green precipitate of copper (II) hydroxide
  • The precipitate is insoluble in excess sodium hydroxide
  • Cu2+ (aq) + 2OH- (aq) —> Cu(OH)2 (s)
• Ion: Fe2+ with NaOH

  • pale green solution reacts to form a green precipitate of iron (II) hydroxide
  • Th precipitate is insoluble in excess sodium hydroxide but turns brown at its surface on standing in air as iron (II) is oxidised to iron (III)
  • Fe2+(aq) + 2OH- (aq) —> Fe(OH)2 (s)
• Ion: Fe3+ with NaOH

  • Pale yellow solution reacts to form n orange-brown precipitate of iron (III) hydroxide
  • The precipitate is insoluble in excess sodium hydroxide
  • Mn2+ (aq) + 2OH- (aq) —> Mn(OH)2 (s)
• Ion: Cr3+ with NaOH

  • Violet solution reacts to for a grey-green precipitate of chromium (III) hydroxide
  • The precipitate is soluble in excess sodium hydroxide forming a dark green solution
  • Cr3+ (aq) —> Cr(OH03 (s) —> [Cr(OH)6]^3- (aq)
  • Cr3+ (aq) + 3OH- (aq) —> Cr(OH)3 (s)
  • Cr(OH)3 (s) + 3OH- (aq) —> [Cr(OH)6]^3-
• • Cr(OH)2 (s) is a blue precipitate which dissolves in excess ammonia to form a deep blue solution with formula [Cu(NH3)4(H2O)2]^3+ (aq)
• • Cr3+ (aq) + 3OH- (aq) —> Cr(OH)3 (s)
  • Cr(OH)3 is a green precipitate which dissolves in excess ammonia to form [Cr(NH3)6]^3+ (aq) which is a purple solution
• • Fe2+, Fe3+ & Mn2+ react with an excess of aqueous ammonia in the same way as they react with aqueous sodium hydroxide, forming precipitates of Fe(OH)2 (s), Fe(OH)3 (s) & Mn(OH)2 (s)
  • There is no further reaction with aqueous ammonia so the precipitates don’t dissolve