Transition Metals

• Define transition metals

  A transition element is a d-block element that forms one or more stable ions with partially filled d orbitals

  
• Define d-block elements


  An element located between Group 2 and Group 13. The 3d sub-shell has the highest energy and electrons added to 3d orbitals
• Electron configuration of transition metals


  To work out the electron arrangement for ions of the d-block: 4s electrons are removed first, followed by the 3d electrons

  
• Why are scandium and zinc not transition metals?


  Although scandium and zinc are in the d-block:-

  -> Scandium (Sc) can only form 3+ ions with an electron configuration of [Ar]3d0 meaning an empty d sub-shell

  -> Zinc (Zn) can only form 2+ ions with an electron configuration of [Ar]3d10 meaning a full d sub-shell

  
• Why is copper classed as a transition metal, despite the fact the Cu+ ion has completely filled d-orbitals (3d104s1)?


  A full d sub-shell provides greater stability for Cu

  -> When an electron from the 4s orbital moves into the 3d orbital to create a more stable 3d sub-shell.
• What are the different types of properties of transition metals that are different from other metals?


  -> They form compounds in which the transition element has different oxidation states

  -> They form coloured compounds

  -> The element and their compounds can act as catalysts
• 1) Variable oxidation states


  Transition elements form compounds with more than one oxidation state.

  -> The number of oxidation states increases across the transition element series to manganese, and then decreases.

  ALL TRANSITION ELEMENTS FORM ELEMENTS WITH OXIDATION NUMBER +2

  
• Give two examples of the existence of more than one oxidation state for each element in its compounds


  Iron (II) chloride

  Iron (III) chloride
• 2) Formation of coloured compounds


  The solid compounds can be dissolved in water to produce coloured solutions

  -> The colour of a solution is linked to the partially filled d-orbital of the transition metal ion.
• Give two examples of the formation of coloured ions


  Iron forms two common oxidation states +2 and +3 in its compounds:-

  -> Iron (II) - Pale green

  -> Iron (III) - Yellow
• What is a catalyst?


  A catalyst is a substance which increases the rate of a chemical reaction, without being changed itself. It works by providing an alternative pathway with a lower activation energy

  
• 3) Transition metals as catalysts


  Transition metals and their compounds of ammonia are important catalysts used in a variety of industrial processes and in the laboratory
• Give two examples of transition metals as catalysts


  -> The Haber process to manufacture ammonia from the reaction between nitrogen and hydrogen is catalysed by iron

  N2(g)+3H2(g)⇌2NH3(g)

  
  

  -> The Contact process in the production of sulfur trioxide from the oxidation of sulfur dioxide is catalysed by vanadium oxide (V205(s))

  2SO2(g)+O2(g)⇌2SO3(g)
• Why are transition metals good catalysts?


  Their variable oxidation states means that by receiving and losing electrons in the d-orbitals reactions can speed up
• What are the Haber process and Contact process examples of?


  Heterogeneous catalysis - As the catalyst is in a different state to the reactants
• What are the benefits of transition metals as catalysts?


  -> They are used to make product faster and can be used to lower temperature required for a reaction:-

  - This saves both energy, money and is better for the environment
• What are the risks of transition metals as catalysts?


  -> Long term exposure to copper can cause damage to the liver

  -> Long term exposure to manganese can cause psychiatric issues and physical tremors
• Define a ligand

  A molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond or a dative covalent bond

  -> Ligands can have no charge, neutral charge or be negatively charged

  
• Define coordination number


  The total number of coordinate bonds formed between a central metal ion and its ligands
• What are monodentate ligands?


  A ligand that is able to donate one pair of electrons to a central metal ion
• Give examples of monodentate ligands


  H20 (neutral)

  NH3 (neutral)

  Cl- (negative)

  OH- (negative)

  
• What are bidentate ligands?


  A ligand that can donate two lone pairs of electrons to the central metal ion, forming two dative covalent/coordinate bonds

  
• Give examples of bidentate ligands


  Ethanedioate

  1,2-diaminoethane (NH2CH2CH2NH2)

  
• What are multidentate ligands?


  Ligands that can form many coordinate bonds

  
• Give an example of multidentate ligands

  
• What is a dative covalent bond/coordinate bond?


  A covalent bond in which a shared pair of electrons is provided by one of the bonding atoms
• Define complex ion


  A central metal ion attached coordinately bonded ligands
• How is a complex ion formed?


  A complex ion is formed when one or more molecules (or negatively charged ions) bond to a central metal ion

  
• How are complex ions represented?

  
• How do you calculate the charge on a complex ion?

  The sum of the charges on the central metal ion and any ligands present
• Give an example of a complex ion and how it is formed?


  [Cr(H2O)6]3+

  -> This is formed when CrCl3∙6H20 is dissolved in water

  -> Cr3+ is the central metal ion

  -> Water acts as a ligand with each water molecule donating a lone pair of electrons from the oxygen atom to the central metal ion to form a coordinate bond

  -> The coordination number is 6 as there are six coordinate bonds to the central metal ion
• Give an example of a six-coordinate complex (octahedral shape)


  This has an octahedral shape with bond angles around the manganese of 90°

  
• What are the two common shapes of four-coordinate complexes (coordination number of four)?


  Tetrahedral complexes

  Square planar complexes
• Tetrahedral complexes


  Bond angle of 109.5° around the central metal ion

  
• Square planar complexes


  A square planar shape occurs in complex ions of transition metals with eight d-electrons in the highest energy d-sub-shell

  -> In this shape, ligands are arranged at the corners of a square (without the ligands above and below the plane)

  
• What are stereoisomers?


  Compounds with the same structural formula, but different arrangements of atoms in space
• What are the two types of stereoisomers that complex ions can display?


  cis-trans isomerism

  optical isomerism

  
• What does the type of isomerism depend on for complex ions?


  ->The NUMBER and TYPE of ligand that are attached to the central metal ion

  -> The shape of the complex
• Why does cis-trans isomerism require a C=C bond?


  A C=C double bond prevents the rotation of groups attached to each carbon atom of the C=C bond

  -> In complex ions, there is no C=C bond
• Cis-trans isomerism in square planar complexes


  Cis isomer -> Two identical groups are adjacent to each other 90 degrees apart in same line

  
  

  Trans -> Two identical groups opposite to each other 180° apart