Transition elements

• Transition element

  elements with partially filled d subshells
• Exceptions of 4s shell filled before 3d shell

  chromium and copper
• Which elements are not transition elements?


  zinc and scandium, as they can’t form stable ions with incomplete d sub shells.

  zinc forms ion zn 3+

  scandium forms ion Sc 3+
• Why are transition elements good catalysts?

  they can change oxidation states by losing/gaining electrons within their d orbitals.

  they can transfer electrons to speed up reactions.

  they are good at absorbing substances onto their surfaces to lower activation energy of reactions
• Problem of using transition elements as catalysts?

  they can cause health risks because they are toxic
• Copper precipitate reaction colour change

  pale blue solution > blue precipitate , deep blue im aqueous ammonis
• iron (II) precipitation reaction

  pale green solution > green precipitate
• Iron (III) precipitate reaction

  yellow solution > rusty brown precipitate
• Manganese precipitation reaction

  pale pink solution > light pink/brown precipitate
• Chromium precipitation reaction

  purple/green solution > green precipitate, dark green in excess naoh, grey green precipitate dissolves in excess aqueous ammonia to form a purple complex ion
• Complex ion

  • transition metal ions bonded to one or more ligands by coordinate bonds
• Ligand

  • molecule or ion that can donate a pair of electrons to the transition metal ion to form a coordinate bond to a metal ion
• Coordinate bond

  • shared pair of electrons in which one of the bonded atoms provides both electrons for the shared pair
• Monodentate ligand: A ligand that can only form one coordinate bond with a metal ion.
• Coordination number is the number of coordinate bonds in a molecule.
• Transition metal complexes with H20 and NH ligands commonly form octahedral complexes with a bond angle of 90°. Octahedral complexes are formed when there is six-fold coordination.
• When complexes form with larger ligands such as Cl, they form tetrahedral complexes with a bond angle of 109.5° and 4 ligands coordinated. Tetrahedral complexes can show optical isomerism.
• Platinum and nickel complexes form in a square planar shape. This consists of four coordinate bonds with a bond angle of 90°.
• This is the cis isomer of a square planar complex of platinum. It has both chlorine atoms on the same side. It is commonly used as a cancer therapy drug. Drugs like cisplatin target components of cells that are chiral, so only one isomer of the drug will be the correct orientation to 'fit' the cells. Therefore, only this single isomer will work and cure the disease.Cisplatin can cause serious side effects such as hair loss, meaning it has to be administered in small amounts to try and reduce these effects whilst still targeting the cancerous cells.
• cisplatin acts by binding to the dna in fast growing cancer cells, this alters the dna structure in the cancerous cells, preventing cell division
• Haem is a multidentate ligand that is found in the molecule haemoglobin, haemoglobin is a protein used to transport oxygen around the body in blood, the structure is octahedral
• Ligand substitution in haemoglobin

  o2 molecule replaced by H2O or CO2
• Carbon monoxide acts as a ligand (electron pair donor) and can bind with haemoglobin. CO binds more strongly than O2 with haemoglobin, ligand substitution can occur. CO binds irreversibly with haemoglobin, in the presence of CO less O2 is transported in the blood, tissues become starved of O2
• Oxidation of Cr(OH)3 produces CrO4 2- which can then be acidified to produce Cr2O7 2-