Transition Metals

• What is a transition metal?

  D-block element that forms at least 1 stable ion with an incomplete d sub-shell.
• Why aren't zinc & scandium transition metals?

  Their stable ions don't have incomplete d sub-levels. Sc3+ has empty d sub-level & Zn2+ has full d sub-level.
• Physical properties of transition metals?

  High density & high melting & boiling point.
• Chemical properties of transition metals?

  Can form complex ions & coloured ions, good catalysts, can exist in variable oxidation states. Incomplete d sub-level causes special chemical properties.
• What is a complex ion?

  Metal ion surrounded by co-ordinately bonded ligands.
• What are ligands?

  Atom, ion or molecule that donates pair of electrons to central metal ion.
• What is a co-ordinate bond?

  Covalent bond where both electrons in shared pair come from same atom.
• Define monodentate, multidentate & bidentate:

  Monodentate= ligands only forming 1 co-ordinate bond. Multidentate= form more than 1 co-ordinate bond. Bidentate= form 2 co-ordinate bonds.
• How do you calculate oxidation state of metal ion in a complex ion?

  Total charge of complex- sum of charges of the ligands.
• What does the shape of a complex ion depend on?

  Its co-ordination number (number of co-ordinate bonds formed with central metal ion). Usual number= 6 & 4. Ligands small-6 can fit around central metal ion. Ligands larger-4 can fit around ion.
• What are the different shapes of complex ions?

  6 co-ordinate bonds-octahedral shape (many are hexaaqua complexes). 4 co-ordinate bonds-tetrahedral shape. Can also form square planar shape. 2 co-ordinate bonds- linear shape.
• When can optical isomerism occur in a complex ion?

  When ion can exist as 2 non-superimposable mirror images. Happens in octahedral complexes when 3 bidentate ligands attached to central ion.
• When can cis-trans isomerism occur in complex ions?

  Square planar complex ions with 2 pairs of ligands. 2 paired ligands opposite eachother =trans isomer. In octahedral complex: 4 ligands of 1 type & 2 ligands of another type.
• What is cisplatin?

  Complex of platinum(2), 2 chloride ions & 2 ammonia molecules, in square planar shape. Treats cancer by preventing cells reproducing.
• Amount of energy needed to make electrons jump depends on what?

  Central metal ion & its oxidation state, ligands & co-ordination number. (These affect size of energy gap).
• What happens when ligands bond to transition metal ions?

  Splits 3d orbitals into different energy levels due to electron repulsion. Electrons tend to occupy lower orbitals (ground state). To jump up to higher orbitals (excited states), need energy equal to energy gap. Get this energy from visible light. Some frequencies absorbed-rest reflected & combine to make complement of colour of absorbed frequencies.
• Why is spectroscopy useful method of measuring conc. of a coloured ion solution?

  Easy to get many readings & can work out conc. quickly. Can measure very low concs. & it doesn't use up any of the substance or interfere with any reactions.
• What is a ligand substitution reaction?

  1 ligand swapped for another ligand-causes colour change. Substitution of similarly sized ligands - co-ordination number & shape of complex ion doesn't change. Different sized ligands- co-ordination number & shape changes.
• Why might a compound look white or colourless?

  All light reflected as there's no 3d electrons or 3d sub-level is full, so no energy absorbed.
• How can spectroscopy be used to measure amount of light absorbed by solution of complex ions?

  White light shone through filter (only lets colour of light through that's absorbed by sample). Light then passes through sample to colorimeter (shows how much light absorbed by sample). More concentrated coloured solution, more light absorbed.
• How would you produce calibration graph to measure conc. of solution of complex ions?

  Measure absorbencies of known concs. of solutions & plot results on graph. Measure absorbance of sample & read its conc. off graph.
• What is hb?


  Blood protein transports O2 around body. Contains Fe2+ ions which are hexa-co-ordinated (6 lone pairs donated to them to form 6 co-ordinate bonds). 4 lone pairs come from nitrogen atoms-form circle around Fe2+ (haem part). Molecule 4 N atoms part of is a multidentate ligand called a porphyrin. Globin protein & either an oxygen or H2O molecule bind to Fe2+ ion to form octahedral structure.
• What happens to hb in the body?

  H2O & O2 bind to Fe2+ ions as ligands, so complex can transport O2 to where it's needed, & then swap it for H2O molecule. In lungs (O2 conc. high) H2O ligands substituted for O2 molecules to form oxyhb. Transports O2, & H2O back on again. Hb returns to lungs & process begins again.
• Why is carbon monoxide poisonous?

  When inhaled, hb can substitute H2O ligands for CO ligands, forming carboxyhb. CO forms strong bond with Fe2+ ion & doesn't readily exchange with O2 or H2O ligands- hb can't move O2. CO poisoning starves organs of O2-causes headaches, dizziness, unconsciousness & death if not treated.
• When can ligand exchange reactions be easily reversed?

  When new complex ion formed is less stable than old one. If new ligands form stronger bonds with central metal ion than old ligands did, change less easy to reverse.
• Why are ligand exchange reactions involving bidentate & multidentate ligands hard to reverse?

  Multidentate ligands form more stable complexes than monodentate ligands.
• Why is enthalpy change for ligand exchange reaction usually very small?

  Strength of bonds broken often very similar to strength of new bonds being made.
• Why do multidentate ligands form more stable complexes than monodentate ligands (chelate effects)?

  When monodentate ligands substituted with bidentate or multidentate ligands, number of particles increases-greater entropy. Reactions resulting in increase in entropy more likely to occur.
• How many oxidation states does vanadium exist in solution?

  4 ( +2 , +3 , +4 & +5).
• What happens when you switch between oxidation states?

  Redox reaction- metal ions either oxidised or reduced.
• How can vanadium be reduced?

  Add it to zinc metal in acidic solution. Solution goes yellow to blue first, then turns green & finally then violet.
• What is a redox potential?

  How easily atom or ion reduced to lower oxidation state ( same as electrode potential). Can vary depending on environment ion is in.
• What does a more positive redox potential indicate?

  Less stable ion is & so more likely reduced.
• How do ligands affect redox potential?

  Standard electrode potentials measured in aqueous solution so any ions will be surrounded by H2O ligands. Different ligands may make potential larger/smaller depending on how well they bind to metal ion in particular oxidation state.
• How does pH affect redox potential?

  Some ions need H+ ions to be present in order to be reduced- others release OH- ions into solution when they're reduced. (pH affects size of redox potential of solution). In general, redox potentials more positive in acidic solutions, as ion more easily reduced.
• In Tollens' reagent, what is the aldehyde added oxidised to?

  Carboxylate anion.
• What is the colour of Tollens' reagent?

  Colourless.
• Formula of complex ion found in Tollens' reagent?

  [Ag(NH3)2]+