3.2.5 Transition metals Flashcards
Transition metal definition
A d-block element with a partially filled d subshell. They lose elctrons to form positive ions
Why are Sc and Zn not considered transition metals
Sc3+ has no electrons in the d subshell
Zn2+ has a complete d subshell so cannot form ions with an incomplete d subshell
Transition metal properties
Form complexes
Form coloured compounds
Have variable oxidation states
Catalytic activity
Ligand definition
A molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons
Complex definition
Central metal atom or ion surrounded by ligands
Coordination number
The number of coordinate bonds to the central metal atom or ion. NOT the number of ligands
Monodentate ligands examples and change in coordination number
H2O - no change in coordination number
NH3 - no change in coordination number
Cl- - change in coordination number (very large)
Ligand substitution reaction
When a ligand(s) replaces another ligand(s), substitution may be incomplete resulting in multiple different ligands in one complex
Why can you have [Cu(H2O)6]2+, but not [Cu(Cl)6]4-
the Cl- ion is much larger than a H2O or NH3 molecule and there is not enough space for 6 chloride ions around a copper ion.
Bidentate ligand examples
H2N-CH2-CH2-NH2 ethane-1,2-diamine (en)
C2O42- ethanedioate
Benzene-1,2-diol
Multidentate ligand example and how many coordinate bonds it can form
EDTA 4-, 6 coordinate bonds
Example of a a multidentate compound
Haem - iron(II) complex with a multidentate ligand
How is oxygen transported in the blood
Fe(II) forms coordinate bonds with a tetradentate ligand. This allows it to form a coordinate bond with oxygen and globin, allowing oxygen to be transported with the blood
Why is CO toxic
Carbon monoxide is toxic because it replaces oxygen coordinately bonded to Fe(II) in haemoglobin.
Chelate effect
Bidentate and multidentate ligands replace monodentate ligands from complexes. This is more thermodynamically stable. This is because the number of species in the system increases so higher entropy which is favoured. And a small ∆H in substitution.
Cis-trans isomerism in complexes
Octahedral complexes, square planar complexes
Involves multidentate ligands
e.g. Cisplatin and Transplatin
Optical isomerism
Octahedral complexes
Involves either:
3 bidentate ligands
2 bidentate ligands and 2 monodentate ligands
1 hexadentate ligand
What transition metal forms linear complexes
Ag in [Ag(NH3)]2+ in tollen’s reagent
How can transition metals be identified
By colour
Why does colour arise in transition metal compounds
Some wavelengths are absorbed, some are reflected or transmitted
What happens to electrons when light is absorbed
They are excited from the ground state to an excited state
The energy difference between the ground state and the excited state equation
∆E = hν = hc ÷ λ
h = Planck’s constant
v = frequency
c = speed of light
λ = wavelength
What can alter ∆E and what does this cause
Change in coordination number
Change in oxidation state
Change in ligand
Causes a change in colour
How can the concentration of coloured ions in solution be measured
With a simple colorimeter
