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
Why do all transition elements show both +1 and +2 oxidation states?
Formed by the loss of 4s electrons.
Why is Chromium (II) prepared by the reduction of Chromium (VI)?
The reduction of chromium (VI) by zinc in acid solution, produces hydrogen which can be used to exclude air since Chromium (II) is easily oxidised to Chromium (III).
NaOH + Chromium (III) salt
A green precipitate is formed which dissolves in excess NaOH to give a green solution containing chromate (III)
What are 3 features of a transition element?
- Coloured ions
- Variable oxidation states
- Catalysis complexes
Why doesn’t hexane react with transition metal ions?
No lone pairs
Why does ethanol react with transition metal ions?
Lone pairs on O
Why do co-ordinate bonds form between transition metal ions and water molecules?
TM ions can accept lone pair and H2O can donate pair.
2 examples of bidentate ligands
- Ethylenediamine
2. C2O
One feature of silver chemistry which isn’t a characteristic of transition elements
Colourless
Analytical method for determining conc. of transition metal ions in a solution
- Colorimetry
2. Atomic absorption
Formula of Zirconium in its highest oxidation state
ZrCl4
Octahedral complex with Iron (III) ions
[Fe(Cr2O4)3]3-
Why are chloride ions outside the bracket not considered to be acting as ligands?
Ionic bonding
1 example of a linear complex formed by a transition metal
- [AgCl2]-
2. [Ag(NH3)2]+
