transition metals

• Properties of transition metals

  1) Variable oxidation states

  2) Catalytic action

  3) Coloured compounds

  4) Formation of complexes
• ligand

  molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons to the bond
• monodentate ligand

  a species that forms only a single coordinate bond to a metal ion in a complex

  eg: H2O

  NH3

  Cl-

  CN-
• bidentate ligand

  a ligand that can form two bonds to a metal ion

  eg: 1,2-diaminoethane (H2NCH2CH2NH2) - en

  ethanedioate ions (C2O4 2-) - ox
• multidentate ligands

  A ligand that forms more than two co-ordinate bonds to the central metal ion

  eg: EDTA 4- --> hexadentate - forms 6 dative covalent bonds
• ligand exchange

  when one ligand in a complex ion is replaced by a different ligand
• colour in transition metals

  -complex soln absorbs wavelengths of light

  -transmits wavelengths of complementary colour
• electron promotion

  when an electron absorbs light energy that then excited it from a 3d orbital of lower energy to one of higher energy
• Planck's constant equation

  deltaE=hv

  h - plancks constant (6.626x10-34 m2kgs-1)

  v - frequency (hertz)
• factors effecting deltaE: type of ligand

  -different ligands will split the d orbital by a diff amount of energy

  -depends of repulsion that d orbital experiences

  -size of deltaE and frequency of of light absorbed by e- will be different

  -different colour absorbed and observed
• Variable oxidation states

  VO2 + (5+) -------> yellow

  VO2+ (4+) -------> blue

  V3+ (3+) -------> green

  V2+ (2+) -------> violet

  (Y)ou (B)etter (G)et (V)anadium
• catalysts

  -speeds up rate without being used up

  -alternate path with lower activation energy

  -heterogenous and homogenous
• heterogenous catalysts

  -different phase or state

  -transition metals are good catalysts due to their variable oxidation states
• absorption

  -a solid catalyst works absorbed molecules onto an active site on the surface of the catalyst

  -active sites increase proximity of molecules and weaken covalent bonds so reactions occur more easily and rate is increased
• catalytic poisoning

  -heterogenous catalysts can be poisoned by impurities which block active sites and prevent absorption

  -bonds of molecules remain strong and catalyst has no effect on ror

  -reaction impurities can lead to an increase in chemical production costs as catalyst has to be replaced or cleaned regularly
• homogenous catalysts

  -catalysts in the same phase
• autocatalysis

  -one of the products can act as a catalyst

  -over time the amount of product increases, ror also increases as it becomes catalysed

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