Transition Metals Flashcards
Chemical properties of transition metals
- Variable oxidation states
- Colour
- Catalysis
- Complex formation
Transition element
One that forms at least 1 stable ion with a part full d-shell of elelectrons
Why are Scandium and Zinc not transition metals?
Scandium only forms Sc 3+, which is d10, in all its compounds and zinc only forms Zn 2+ (3d10) in all its compounds.
Ligand
An ion or molecule with a lone pair of electrons that forms a co-ordinate bond with a transition metal
Complex ion
A transition metal ion surrounded with 2,4 or 6 ligands
Co-ordination number
Number of co-ordinate bonds to ligands that surround the d-block metal ion
Ions with co-ordination number 6
Octahedral
Ions with co-ordination number 4
Tetrahedral
Multidentate ligands
More than 1 lone pair that can bond to a transition metal ion
EDTA
A hexadentate ligand that can use lone pairs on 4 oxygen an both nitrogen atoms.
Chelates
Complex ions with polydentate ligands
Haemoglobin
Fe2+ ion with co-ordination number 6. 4 co-ordination sites are taken up by a porphyrin ring which acts as a tetradentate ligand. Below the plane of this ring is a 5th nitrogen acting as a ligand. The 6th site can accept an oxygen molecule as a ligand.
Why does [CoCl4]2- ion have 4 ligands and [Co(NH3)6]3+ ion have 6 ligands?
Chloride ion is a larger ligand than the ammonia molecule, so fewer ligands can fit around the central metal ion
Why are transition metal complexes coloured?
- Part-filled d-orbitals
- Possible for electrons to move from one d-orbital to another
- In an isolated transition metal atom, all d-orbitals are of exactly the same energy, but in a compound, the presence of other atoms nearby make the d-orbitals have slightly different energies
- When electrons move from 1 d-orbital to another of a higher energy level, they often absorb energy in the visible region of the spectrum equal to the difference in energy between levels
- The colour is therefore missing from the spectrum and we see the combination of the colours that are not absorbed
Why is a colorimeter used?
To find the ratio of metal ions to ligands in a complex