Transition metals

• What are transition metals?

  elements with an incomplete d sub shell in atoms or ions
• transition metals that have different electron configuration to the rest?

  chromium and copper
• Why do chromium and copper have different electron configuration?

  so more stable (4s1)
• Characteristics of transition metals

  -coloured ions

  -complex formation

  -variable oxidation stated

  -catalysts
• Why is zinc not a transition metal?

  can only form 2+ ions, the ion has a complete d orbital so does not meet the criteria of having an incomplete d orbital
• Complex

  central metal ion surrounded by ligands
• Ligand

  atom or ion that can donate a lone electron pair
• What type of bonding is involved in complexes?

  coordinate bonding
• Coordinate bonding

  shared pair of electrons in a covalent bonds come from only one boning atom
• Coordination number

  -number of coordinate bonds formed to the metal ion
• Monodentate ligands examples

  -H2O, NH3, Cl-
• What is a monodentate ligand?

  can only form one coordinate bond per ligand
• Bidentate ligands

  can form 2 coordinate bonds per ligand
• Bidentate ligands examples

  -NH2CH2CH2

  -C2O4 -2
• Multidentate ligand

  can form more than 2 coordinate bonds per ligand
• How many coordinate bonds can EDTA4- form?

  6
• similarities of NH3 and H2O

  -small

  -no charge

  -can form 6 coordinate bonds
• Substitution reaction between NH3 and H2O does not change the coordination number
• Addition of high concentration of chloride ions to aqueous ions lead to ligand substitution
• Chloride ligand vs H2O and NH3

  • all are monodentate
  • Cl- is larger, can only fit 4 atoms
• Ethane 1-2 diamine as ligand

  3 bidentate ligand in complex, 6 coordination no.
• Ethandioate as ligand

  3 bidentate ligand in complex, 6 coordination no.

  -octehedral

  • 90'
• molecular formular for Ethane 1-2 diamine

  NH2CH2CH2NH2
• Molecular formula for ethanedioate

  C2O4 -2
• Partial substitution of ethanedioate ions. When dilute aqueous solution of ethanedioate ions added to solution containing aqueous Cu2+ ions, 4 water molecules removed
• Why are only 4 molecule of water of removed when 2 molecule of ethanedioate ions are substituted?

  Because each ethanedioate atom is a bidentate ligand, 2 lone pairs from each O atom can be donated to form coordinate bonds
• draw displayed formula of EDTA 4-


  1

  
• Another multidentate ligand that is not EDTA 4-

  Haem - iron complex
• How does Haem operate as a multidentate ligand

  oxygen form coordinate bonds to FE(II) in haemoglobin, enabling oxygen to be transported in the blood
• How is CO toxic to humans?

  CO can form strong coordinate bonds with haemoglobin, stronger than oxygen so replaces oxygen and attaches to haemoglobin
• What is the chelate effect?

  the substitution of monodentate ligands with bidentate ligands leads to more stable complexes and positive entropy change
• An example of the chelate effect

  copper complex from having monodentate ligands to multidentate ligands

  [Cu(H2O)6]2+ + EDTA4- -> [Cu(EDTA)]2- + 6H2O
• How does having bidentate or multidentate ligands in a complex increase entropy?

  increase in entropy, more moles of products than reactants, creating more disorder
• How does enthalpy change when a bidentate or multidentate is substituted?

  enthalpy change is small because similar number of bonds in both complexes
• What will the Gibb's free energy value be when the chelate effect occur?

  G will be negative because enthalpy change will be small and entropy change will be positive
• Chelate effect overall

  -increase entropy, more mole in products than reactants so more disorder

  -enthalpy change is small

  -Gibb's will be negative because entropy is positive and enthalpy will be small
• What are EDTA complexes used for?

  -added to rivers to remove poisonous metal ions as EDTA complex are not toxic

  -in shampoos to remove calcium ions in hard water, help lathering
• [Co(NH3)6)2+ + 3NH2CH2CH2NH2 ->[Co(NH2CH2CH2NH2)3]2+ +6NH3

  -increase entropy

  -enthalpy change is close to 0, no. of coordinate bonds are the same, so energy to break and form bonds are the same
• shape of cisplatin

  square planar
• shape of [Ag(NH3)2)+]

  linear