3.2.5 Transition metals

• Define transition metal

  A d-block element that can form at least 1 stable ion with a partially filled d-subshell
• Why do Cr and Cu have a configuration of 4s1?

  An electron from the 4s orbital moves into the 3d orbital to create a more stable full / half full 3d sub-shell
• Why is Scandium not a transition metal?

  It's only stable ion is Sc3+ which has an empty d subshell
• Why is Zinc not a transition metal?

  It's only stable ion is Zn2+ which has a full d subshell
• Properties of transition metals

  Variable oxidation states

  Form coloured ions

  Form complex ions

  Act as catalysts
• Colour of V2+ in solution

  Violet
• Colour of V3+ in solution

  Green
• Colour of VO$^{2+}$ in solution


  Blue
• Colour of VO2 + in solution

  Yellow
• Define complex ion

  A central transition metal surrounded by ligands bonded by dative covalent bonds
• Define ligand

  An atom, ion or molecule with at least 1 lone pair of electrons
• What are monodentate ligands?

  Ligands with only 1 lone pair of electrons
• List 3 monodentate ligands

  H2O

  NH3

  CL-
• What are bidentate ligands?

  Ligands with 2 lone pairs of electrons
• Give 2 bidentate ligands

  Ethanedioate

  Ethane-1,2-diamine
• What is a mulitdentate ligand?

  Ligands that form more than 1 co-ordinate bond
• Give an example of a multidentate ligand. How many co-ordinate bonds does it form?

  EDTA4-

  6
• Define coordination number

  The number of co-ordinate bonds in a complex
• How many H2O and NH3 ligands fit around the central ion?

  6
• How many Cl- ligands fit around the central ion?

  4
• How many ethanedioate and ethane-1,2-diamine ligands fit around the central ion?

  3
• When do complexes have a square planar shape?

  When the central ion is Pt
• What is the difference between cis and trans isomers?

  Cis - Same ligands are on same side

  Trans - Same ligands are on opposite sides
• When an electron absorbs light energy it moves from the ground state (lower energy level) to the excited state (higher energy level)
• The d-subshell splits into 2 when ligands bond to the central ion
• For the electron to move to the higher energy level the light energy must be equal to $\Delta$E
• The size of $\Delta$E depends on...


  The central metal ion and it's oxidation state

  The type of ligand

  The coordinate number
• Multidentate ligands are more stable than monodentate ligands
• Define the chelate effect

  Tendency for bi/multidentate ligands to be substituted for monodentate ligands in a complex ion due to large increases in entropy
• What can be used to reduce V2+ ions?

  Zinc in an acidic solution
• Define heterogeneous catalyst

  A catalyst that is in a different phase / state as the reactants
• Define homogenous catalyst

  Catalysts that are in the same phase as the reactants

  They form an intermediate with the reactants but are then reformed
• Contact process equations


  V2O5 + SO2 -> V2O4 + SO3

  V2O4 + 1/2O2 -> V2O5
• How do heterogenous catalysts work?

  Reactants are adsorbed to the active site of the catalyst

  Reaction takes place

  Products are desorbed
• State 4 ways to change the colour of a transition metal complex

  Change the ligand

  Change the co-ordination number

  Change the oxidation state

  Change the metal
• Why are transition metal complexes in aqueous solutions coloured?

  Some frequencies of visible light are absorbed to excite electrons in the d subshell

  Remaining frequencies of light are reflected or transmitted, making the solution appear coloured