Transition metals (A-level) Flashcards
Define a transition metal.
- A d-block element that forms at least one ion with an incomplete d sub-shell.
Why are Sc and Zn not considered transition metals? (3)
- Sc³⁺ has no electrons in the d sub-shell
- Zn²⁺ has a full d sub-shell (3d¹⁰)
- Transition metals must have partially filled d-orbitals
What are the typical properties of transition metals?
- Variable oxidation states
- Form coloured compounds
- Form complex ions
- Act as catalysts
- Show paramagnetism (due to unpaired d electrons)
Define a ligand and give two examples. (2)
- A ligand is a molecule or ion that donates a lone pair to a central metal ion to form a coordinate bond.
- Examples: H₂O, NH₃, Cl⁻, CN⁻, EDTA⁴⁻
What is the coordination number of a complex ion?
- The number of coordinate bonds formed between the central metal ion and ligands.
- Describe the shape and give an example of a complex with:
(a) coordination number 6
(b) coordination number 4
(a) Octahedral – e.g. [Fe(H₂O)₆]³⁺
(b) Tetrahedral – e.g. [CuCl₄]²⁻
OR
Square planar – e.g. [Ni(CN)₄]²⁻
What is a bidentate ligand? Give an example. (2)
- A ligand that donates two lone pairs to the central ion, forming two coordinate bonds.
- Example: Ethane-1,2-diamine (en) or C₂O₄²⁻
What is a chelate complex and why is it more stable?
A complex ion containing multidentate ligands.
It is more stable due to the chelate effect – entropy increases when multiple ligands are replaced by fewer multidentate ligands.
Why do transition metal complexes show colour? (3)
- d-orbitals split into two energy levels in a complex
- Electrons absorb specific frequencies of visible light to move between levels
- The remaining light is transmitted/reflected as colour
What factors affect the colour of a complex? (4)
- Identity of metal ion
- Oxidation state
- Type of ligand
- Coordination number
Write an equation for the ligand substitution of [Cu(H₂O)₆]²⁺ with excess NH₃ (2)
- [Cu(H₂O)₆]²⁺ + 4NH₃ → [Cu(NH₃)₄(H₂O)₂]²⁺ + 4H₂O
- Pale blue → deep blue
What happens when [Cu(H₂O)₆]²⁺ is mixed with HCl (concentrated)? (4)
- Ligand substitution:
[Cu(H₂O)₆]²⁺ + 4Cl⁻ ⇌ [CuCl₄]²⁻ + 6H₂O - Pale blue → yellow/green
- Coordination number changes from 6 to 4
- Shape changes from octahedral to tetrahedral
Give an example of a redox titration involving transition metals. (2)
- Fe²⁺ + MnO₄⁻ → Fe³⁺ + Mn²⁺
- Acidified KMnO₄ is used to oxidise Fe²⁺ to Fe³⁺
Explain autocatalysis in the reaction between MnO₄⁻ and C₂O₄²⁻. (3)
- Mn²⁺ is a product that also acts as a catalyst
- It increases the rate once formed, by allowing an alternative redox route
- This is autocatalysis
Name two industrial catalysts involving transition metals. (2)
- Fe in the Haber Process (N₂ + 3H₂ ⇌ 2NH₃)
- V₂O₅ in the Contact Process (SO₂ + ½O₂ ⇌ SO₃)
How do heterogeneous transition metal catalysts work? (4)
- Reactants adsorb onto the surface
- Bonds weaken → reaction occurs
- Products desorb
- Surface provides an alternative reaction pathway with lower activation energy
Why do transition metals show variable oxidation states? (2)
- Small energy difference between 3d and 4s sub-shells
- Allows loss of different numbers of electrons in redox reactions
