Transition Elements

• Transition elements

  D block elements that form at least one ion with an incomplete d sub shell
• Why are Sc and Zn not transition metals?

  -Do not form ions with incomplete d-sub shell

  -Sc³⁺ = empty d-sub shell

  -Zn²⁺ = full d-sub shell

  -do not form coloured compounds

  need electrical configuration of elements and ions
• 4s is at a lower energy level than 3d:

  -electrons fill 4s before 3d

  -when ions are formed, electrons are lost from 4s before 3d
• anomalies in transition elements

  -Chromium: 3d and 4s are half filled

  1s²2s²2p⁶3s²3p⁶4s¹3d⁵

  -Copper: 3d full and 4s is half filled

  1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰

  filled like this for increased stability
• Properties

  -High boiling and melting point

  -form coloured compounds

  -conductors of heat and electricity

  -form ions with a variety of different oxidisation states

  -its elements and compounds can act as catalysts

  -forms compounds in which transition elements have different oxidation states
• What properties to transition metals are different to other metals?

  -form coloured compounds

  -its elements and compounds can act as catalysts

  -forms compounds in which transition elements have different oxidation states
• a species containing a transition element in its highest oxidation state is often a strong oxidising agent
• Oxidation states increase to Mn and then decrease
• all transition elements (Ti-Cu) can form ions with a +2 charge. This is because the 4s sub-shell has emptied (2 electrons have been removed)
• What is a catalyst?

  Substance that increases the reaction rate without being used by the overall reaction. It allows the reaction to proceed via an alternate route with a lower activation energy
• What is a homogenous catalyst?

  -A catalysts with the same state as the reactants
• Homogenous catalysts examples

  1.) Cu²⁺(aq) for the reaction of Zn with acids

  • Zn(s) + H₂SO₄ (aq)—> ZnSO₄ (aq) + H₂ (aq)

  2.) Fe²⁺(aq) for reactions between iodide ions and peroxodisulfate ions

  • S₂O₈ ²⁻ (aq)+ Fe²⁺(aq) —> 2SO₄²⁻(aq) + Fe³⁺(aq)
  • Fe³⁺(aq) + 2I⁻(aq) —> I₂ (aq) + Fe ²⁺(aq)

  the iron reacts and is then regenerated
• Heterogenous catalyst examples

  1.) Finely divided Iron catalyst for the process of manufacturing ammonia (HABER PROCESS)

  • N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)

  2.) V₂O₅ (s) Vandium (VI) oxide for the production of sulfur trioxide (CONTACT PROCESS)

  • 2SO₂ (g) + O₂ (g) ⇌ 2SO₃ (g)

  3.) Ni (s) in the hydrogenation of vegetable fats to make margarine

  4.) MnO₂ (s) Manganese (IV) oxide in the decomposition of hydrogen peroxide (H₂O₂)

  • 2H₂O₂ (aq) —> 2H₂O (l) + O₂ (g)
• How do catalysts work?

  -Adsorption: reaction takes place on the surface of the metal. Reactants are weakly adsorbed onto the surface which weakens the bonds and allows the reaction to take place.

  -Changing oxidation state: transition metal ions gains/loses electrons and then gets regenerated at the end of the reaction
• what is a complex ion?

  A complex ion is a charged species consisting of a central metal ion bonded to surrounding ligands.
• What is a ligand?

  A ligand is a molecule or ion that binds to a central metal atom or ion in a coordination complex by donating a pair of electrons
• What is a dative covalent bond?

  Covalent bond where one of the bonded atom provides both of the electrons for the shared pair
• What is the coordination number?

  Indication of the number of coordinate/dative covalent bonds attached to the central (metal) ion
• What is a mono-dentate/unidentate ligand?

  -Ligand that is able to donate 1 pair of electrons to the central ion

  -1 coordinate bond per ligand

  -H₂O: , :NH₃ , :Cl⁻ , :CN⁻ , :OH⁻
• What is a bidentate ligand?

  Species with two lone pairs of electrons that can form two dative covalent bonds

  Examples: ethandioate and 1,2-diaminoethane

  
• What is a multidentate ligand?

  Species with multiple lone pairs of electrons able to donate many electrons and form many dative covalent bonds to the central ion

  example: EDTA⁴⁻, this has 4 carboxylate groups and forms 6 coordinate bonds
• Coordination number of 6= Octahedral

  Coordination number of 4 = Tetrahedral or square planar
• The stability of an octahedral complex depends on the size of the central ion relative to the radius of the ligand.
• Shapes of complex ions

  Octahedral- bond angle of 90, 6 coordinate bonds

  Square planar- bond angle of 90, 4 coordinate bonds

  Tetrahedral- bond angle of 109.5, 4 coordinate bonds

  Examples:

  
• Stereoisomerism in complex ions

  CIS-TRANS ISOMERISM IN SQUARE PLANAR

  • must have no more than two identical ligands attached to the central ion
  • CIS= 2 identical groups/ligands are adjacent to each other (90 degrees apart)
  • TRANS= 2 identical groups/ligands are opposite each other (180 degrees apart)

  EXAMPLE:

  
• Stereoisomerism in complex ions


  CIS-TRANS ISOMERISM IN OCTAHEDRAL

  • monodentate ligands: 4 of one type, 2 of the other
  • bidentate ligands: 2 of the type
  • CIS= 2 identical groups/ligands are adjacent to each other (90 degrees apart)
  • TRANS= 2 identical groups/ligands are opposite each other (180 degrees apart) OPTICAL ISOMERISM CAN OCCUR IN THE CIS ISOMER BUT NOT IN THE TRANS ISOMER
• Optical isomerism in octahedral real complexes

  -contains 2 or more bidentate ligands (can be seen with 3 bidentate ligands)

  -NON SUPERIMPOSABLE MIRROR IMAGE

  -cis isomer can form optical isomers but trans isomers cannot
• What is the role of cis-trans isomerism in medicine?

  -when scientists researched the effect on electrical fields on bacteria using platinum electrodes the colony of E-Coli failed to divide but continued to grow

  -Cis-platin attacks tumours and in many cases shrinks them in size

  -However, there are side effects like kidney damage

  -Cis-platin forms a platinum complex inside the cells which binds to DNA and prevents the DNA of the cell from replicating

  -this leads to activation of the cells own repair mechanism and eventually leads to apoptosis
• What is a ligand substitution?


  When a ligand in a complex ion is replaced by another ligand
• Haemoglobin

  4 protein chains (polypeptides) held by weak intermolecular forces. Each contains a heme group which contains the central metal ion of Fe2+ which binds to oxygen
• Reactions of aqueous copper (II) ions [Cu(H₂O)₆]²⁺:

  With excess aqueous NH₃ (aq):

  [Cu(H₂O)₆]²⁺ (aq) + 4NH₃ (aq) → [Cu(NH₃)₄(H₂O)₂]²⁺ (aq) + 4H₂O(l)

  -pale blue solution to deep/darker blue solution. (The two water molecules are above and below the octahedral when drawn - north and south)
• Reactions of aqueous copper (II) ions [Cu(H₂O)₆]²⁺:

  With excess aqueous NH₃ (aq):

  -four ammonia ligands have replaced four of the water ligands-Adding NH₃ drop-wise will form a pale blue precipitate of Cu(OH₂)

  -Adding excess NH₃ will mean the precipitate dissolves to form a dark blue solution 

  -pale blue solution to deep/darker blue solution
• Reactions of aqueous copper (II) ions [Cu(H₂O)₆]²⁺:

  With Chloride ions using concentrated HCl

  [Cu(H₂O)₆]²⁺ (aq) + 4Cl⁻ (aq) ⇌ [CuCl₄]²⁻ (aq) + 6H₂O(l)  

  -pale blue solution to yellow solution

  -octahedral to tetrahedral
• Reactions of aqueous copper (II) ions [Cu(H₂O)₆]²⁺:

  With Chloride ions using concentrated HCl:

  -four chloride ligands have replaced all six of the water ligands (chloride ligands are larger than the water ligands so fewer fit around the central ion

  -pale blue solution to a yellow solution

  -If water is added to the yellow solution, a blue solution would form but this would be more dilute and paler than the original colour

  -green is the intermediate colour as blue and yellow mix
• Reactions of aqueous chromium (III) ions [Cr(H₂O)₆] ³⁺:

  -When KCr(SO₄)₂·12(H₂O)₂ (Chromium (II) potassium sulfate) is dissolved in water, the complex ion  [Cr(H₂O)₆] ³⁺ is formed

  -this is a pale purple solution

  -When Chromium (III) Sulfate is dissolved in water, the complex ion  [Cr(H₂O)₅SO₄]⁺ is formed

  -this is a green solution
• Reactions of aqueous chromium (III) ions [Cr(H₂O)₆] ³⁺:

  [Cr(H₂O)₆] ³⁺ (aq) + 6NH₃(aq) → [Cr(NH₃)₆] ³⁺ (aq) + 6H₂O(l)  

  -violet to purple

  -adding NH₃(aq) dropwise forms a grey-green precipitate of Cr(OH)₃

  -adding excess  NH₃(aq) means the precipitate dissolves to form a purple colour 
• Ligand substitution and Haemoglobin

  -Hb binds to O₂ as blood passes through the lungs due to increased oxygen pressure in the capillaries of the lung

  -Oxyhaemoglobin forms which is a complex ion

  -Hb in red blood cells can also bind to CO₂ which is carried back to the lungs and released via exhalation
• Ligand substitution and Haemoglobin

  -carbon monoxide can also bind to the Fe2+ ion

  -Carboxyhaemoglobin is formed which is a complex ion

  -Ligand substitution occurs if carbon monoxide is inhaled and it replaces oxygen

  -carbon monoxide binds stronger to Hb than oxygen does and so prevents oxygen from binding

  -bond between carbon monoxide and Fe2+ is permanent

  -if conc of carbon monoxide is too high, oxygen transport is prevented and can result in death
• What is a precipitation reaction?

  When two aqueous solutions containing ions react together to form an insoluble ionic solid
• Reactions with NaOH (aq)

  Insoluble in excess sodium hydroxide:

  Cu²⁺ ions (Copper (II) ions)

  Cu²⁺ (aq) + 2OH⁻ (aq) → Cu(OH)₂ (s)

  Blue → blue precipitate