Transition metals

• Transition metals are d block elements that can form at least one stable ion with an incomplete d sub level this would be from Titanium to Copper
• When transition metals form ions, the 4s electrons are removed before 3d electrons. This means that nearly all of them make stable 2+ ions
• Physical properties of transition metals:

  • High density
  • High boiling and melting point
  • Malleable
• Chemical properties of transition metals (caused by incomplete d sublevels):

  • Form complex ions
  • Form coloured ions
  • Good catalysts
• Complex ions

  A complex consists of a central metal ions surrounded by ligands forming coordinate/dative bonds with the ions
• A ligand is an ion or molecule with a lone pair of electrons that form a dative covalent bond with the central ion
• Coordination number is the number of coordinate/dative bonds in a transition metal ion complex
• Oxidation number is the oxidation state of the central metal ion
• Ligands are classified by the number of dative covalent or coordinate bonds they make
• • Monodentate/Unidentate - Only form one dative bond e.g. H2O, OH-, Cl- and NH3
  • Bidentate - Can form 2 dative bonds e.g. ethane-1,2-diamine (en) as both nitrogen atoms donate lone pairs to metal ions. And ethanedioate (C2O4 2-) as the two single bonded oxygen atoms both donate lone pairs
  • Multidentate - form multiple dative bonds
• Naming bonding atoms in ligands:

  • H2O = Aqua
  • NH3 = Ammine
  • OH- = Hydroxo
  • CN- = Cyano
  • Cl- = Chloro
• 4 shapes of complex ions :

  • Linear
  • Square planar
  • Tetrahedral
  • Octahedral
• Complexes have different shapes due to the coordination number and size of ligands
• Multidentate example is EDTA 4- ions which form 6 coordinate bonds

  
• Square planar e.g. is nickel ( || ) tetracyano ion

  • Has a charge of 2-
  • Has a coordination number of 4.
• Tetrahedral e.g. is cobalt (||) chloride ion

  • Has a 2- charge
  • Has a coordination number of 4

  
• Cis-trans isomerism occurs because ligands cannot rotate around the central metal ion. Formed by complexes with monodentate ligands.
• Platin can either be cisplatin or transplatin with cisplatin having the same formula group 90 ° from each other while transplatin has them 180 ° from each other
• Which platin is the diagram?

  Cisplatin

  
• Which platin is in the diagram?

  Transplatin

  
• Different steriosomers can have different chemical properties e.g. Cisplatin is an isomer which is an anti cancer drug but transplatin has no medical uses
• Cis-trans in octerhedral complex ion can happen if they have 4 ligands of one type and 2 of another

  • If the 2 odd ligands are opposite each other (180 °) they are trans
  • If the 2 odd ligands are next to each other (at least 90 ° ) they are cis
• Cisplatin is injected into cancer patients as they are useful in treating solid tumours as it prevent DNA from unwinding by forming coordinate bonds with DNA bases so DNA can't replicate
• Disadvantage of cisplatin:

  • It also affects healthy cells
  • Loads of side effects
  • If patient has too much of it they could be come resistant to it
• Optical isomerism is where a molecule can exist as two forms that are non superimposable mirror images of each other (left and right hand).

  • Formed by octahedral complexes with bidentate ligands
• Most transition metal compounds appear coloured because they absorb energy corresponding to certain parts of visible electromagnetic spectrum.

  • The colour seen is part of the visible spectrum that aren't absorbed e.g. a red compound will absorb all frequencies of the spectrum apart from red light
• Light can be either be transmitted or reflected through or off an object
• Since the d sub level is only partially filled. This means that electrons can move between orbitals
• In transition metal atoms all of the d sub level orbitals sit at the same energy level but when an ion or compound is formed, the energy of the orbitals differ
• The difference in energy between the d sub levels orbitals can be called ∆E
• The frequency of light which provide the ∆E can be found using the following equation ∆E = hv

  • h is plank constant
  • v is the frequency of light
• To work out frequency of light you can use the following equation v = c ÷ λ

  • v is the frequency of light
  • c is the speed of light
  • λ is the wavelength
• Factors affecting colours of transition metals:

  • Size of ligands
  • Type of ligands
  • Coordination number
  • Oxidation number
  • The transition metal ion
• Ultraviolet-visible spectroscopy (UV - Vis) can be used to determine the concentration of a transition metal complex solution.

  • It passes light through a filter and then through a sample. Some of the light is absorbed while the rest pass through
  • Then a colorimeter is used to measure the absorbance of the sample. The amount of light absorbed is proportional to the concentration of the absorbing species
• Method to determine unknown concentration of transition metals

  1. First, add an alternative ligand to intensify the colour e.g. thiocyanate (SCN-) or bipyridyl
  2. Then, make up solutions of known concentrations
  3. Measure the absorption of unknown concentration
  4. Plot calibration curve
  5. Test unknown and use calibration curve to find the concentration
• Red = Low energy light

  Orange |

  Yellow |

  Green |

  Blue |

  Indigo ↓ 

  Violet = High energy light
• If a transition metal complex has a large ∆E between d orbitals, it will absorb light from the high energy level so it appears red, orange or yellow as light from low energy level will be transmitted / reflected
• If a transition metal complex has a small ∆E between d orbitals, it will absorb light from the low energy level so it appears blue, indigo or violet as light from high energy level will be transmitted / reflected
• A ligand substitution reaction occurs when a ligand in a complex ion is replaced by another type of ligand molecules substitution can be by:

  • Of similarly sized ligands ( e.g. 6H2O replaced with 6NH3)
  • Of different sized ligands (e.g. 6H2O replaced with 4Cl-)
  • Partial substitution
• Ligand substitution - different sized

  • When concentrated HCl is added to a solution of hexaaquacopper (||), the chloride ions replace the water molecules as ligands.
  • Equation: [Cu(H2O)6]2+ + 4Cl- ---> [CuCl4]2- + 6H2O
  • The 4H+ ions are spectator ions
  • Since Cl ions are bigger then water only 4 can fit this would change the shape from the octahedral to tetrahedral and the coordination number
  • Colour change from blue to green