Transition Metals OCR
• Which d block elements are/aren't transition metals (very recent
question)
• Overview of different shapes and ligands including haemoglobin
• Stereoisomerism in complex ions including a look at how cisplatin
works
• Precipitation and ligand sub reactions.
• Cheat-sheet within PowerPoint
• A glance at last 3 years of transition metal OCR questions and
PREDICTED QUESTIONS for this year's examination
• How to access a huge variety of practice questions for this topic.
What is a transition metal?
A d block element that forms an ion with a partially filled d subshell
So, which of the 3d elements are transition
metals and which ones aren’t?
Sc - 1s22s22p63s23p64s23d1
Fe- 1s22s22p63s23p64s23d6
Fe2+
-
1s22s22p63s23p63d6
Fe3+ - 1s22s22p63s23p63d5
Sc3+ - 1s22s22p63s23p6
Iron is a typical
transition metal
Cu - 1s22s22p63s23p64s13d10
Cu+ - 1s22s22p63s23p63d10
Cu2+ - 1s22s22p63s23p63d9
Fe3+ - [Ar]
Zn - 1s22s22p63s23p64s23d10
Zn2+ - 1s22s22p63s23p63d10
Although its atom is
partially filled, its only
common ion is NOT
therefore it’s NOT a
transition metal
Cu2+ has a partially
filled 3d subshell
therefore copper IS
a transition metal
Filled d subshell
therefore NOT a
transition metal
The incomplete d sub-shell is responsible for several general
properties of transition elements:
1) Variable oxidation state
2) Catalytic action
3) Coloured compounds
Just to contrast- Aluminium is a
group 3 element. NOT a
transition metal and it is a
white solid that forms
colourless solutions
4) Formation of complexes
This is the focus of the topic
DISSOLVE IN
WATER
SO42- ion
Water molecule from solution
This is the formula of the
complex ion and it is how all
metal ions exist in aqueous
solution
Cu2+(aq) = [Cu(H2O)6]2+
CuSO4
Cu2+ ion
Complex ions are not found on their own – there is always an
oppositely-charged ion to balance the charges although we may ignore
it much of the time. We may focus on the [Cu(H2O)6]2+ ion when we
dissolve copper(II) sulphate in water, forgetting the SO42- ion is also
present in equal concentrations.
What does this complex ion look like in more detail?
How does the copper interact with the water?
Water molecule from solution
Cu2+(aq) = [Cu(H2O)6]2+
Cu2+ ion
Ligand = particle with lone pair of electrons that bonds to metals by a co-ordinate bond
Complex = metal ion with coordinately bonded ligands (also called a dative covalent bond)
Co-ordination number = number of co-ordinate bonds from ligands to metal ion
The possible shapes on complex ions
Types of ligands
All ligands must have one (or more) lone pair(s) of electrons to form the co-ordinate bond(s) to the metal
ion.
Monodentate ligands – ligands which form one co-ordinate bond to a metal ion
NEUTRAL
2+
3+
1+
2+
3+
Its important to recognise whether a ligand has a charge or if it’s neutral this will effect the
overall charge of the complex ion
Bidentate ligands – ligands which form two co-ordinate bonds to a metal ion. There
will be 2 atoms on the molecule than are both capable of donating a lone pair
These are the main 2 examples of bidentate ligands
NEUTRAL
The exam could bring up some unfamiliar
examples of bidentate ligands e.g.
2- ION
Task- draw a 4 coordinate square planar
complex ion involving the bidentate ligand
above and an ethanedioate ion bonded to
central Pt2+ ion
At first glance it looks like the
coordination number is 4 but look closely
at the type of ligands involved.
A couple of bidentate ligands and also
a couple on monodentate results in a
coordination number of 6
Note- Cl- can act as a ligand and an
anion so its possible the anion here
could also be Cl-
Haemoglobin
6th binding site for O2 or H2O
Porphyrinmultidentate
ligand
Globin- a
protein
molecule
Stereoisomerism Recap in Organic Chemistry
E/Z or cis-trans
Optical Isomerism
Non-superimposable mirror images
Stereoisomerism in Complex Ions
Square planar
The Cisplatin version only works as two chloride ions are displaced and
the molecule joins on to the DNA. In doing this it stops the replication
of cancerous cells.
Pt(NH3)2Cl2
Cisplatin prevents DNA replication in cancer cells by a ligand
replacement reaction with DNA in which a dative covalent bond is
formed between platinum and a nitrogen atom on guanine
Cisplatin or
Z-platin
Transplatin or
E-platin
The N and O atoms marked in red can’t
bond to cis-platin as they are involved in the
bonding within the DNA molecule
Bonus mark
Q7
[Co(NH3)4Cl2]+
Cis or Z
A 2/4 coordination number split between the ligandslook to see where the 2 are relative to one another
Trans or E
Optical Isomerism
• Octahedral
• 2 or 3 bidentate ligands
Precipitation and ligand substitution reactions
For the precipitation
reactions with NaOH, if the
charge is 2+, it will react
with 2 OHIf the charge is 3+ it will
react with 3
[Cu(H2O)6]2++ 2OH-  Cu(H2O)4(OH)2 + 2H2O
No overall charge suggests a precipitate
Write the equivalent equation for an aqueous Cr3+ solution and NaOH
[Cr(H2O)6]3++ 3OH-  Cr(H2O)3(OH)3 + 3H2O
[Cr(H2O)6]3++ 3OH-  Cr(H2O)3(OH)3 + 3H2O
Excess NaOH
Cr(H2O)3(OH)3 + 3OH-  [Cr(OH)6]3- + 3H2O
Green precipitate
Dark green solution
For the precipitation
reactions with dropwise
NH3, if the charge is 2+, it
will react with 2 NH3
If the charge is 3+ it will
react with 3
[Cu(H2O)6]2++ 2NH3  Cu(H2O)4(OH)2 + 2NH4+
No overall charge suggests a precipitate
Dropwise NH3 = precipitation
[Cu(H2O)6]2+ + 2NH3  Cu(H2O)4(OH)2 + 2H2O
Excess NH3 = Ligand substitution
No overall charge suggests a precipitate
Pale blue precipitate
[Cu(H2O)6]2+ + 4NH3  [Cu(H2O)2(NH3)4]2+ + 4H2O
Deep (royal) blue solution
trans or E
[Cr(H2O)6]3+ is the other complex ion that will react with an excess of ammonia via
ligand substitution, suggest an equation. Write the equation for this ligand
substitution reaction.
HINT- It reacts with a different number of NH3 molecules to the Cu2+ and forms a
complex ion with NO cis/trans isomerism.
[Cr(H2O)6]3+ + 6NH3  [Cr(NH3)6]3+ + 6H2O
If concentrated hydrochloric acid is added to a
solution containing Cu2+ (aq),the solution turns green and
progressively more yellow as chloride ligands replace
the water molecules. The new complex is yellow, but
the solution containing both complexes appears green.
Another ligand
substitution reaction
[Cu(H2O)6]2+ + 4Cl- ⇌ [CuCl4]2- + 6H2O
octahedral
tetrahedral
(aq) metal ions
[Cu(H2O)6]2+
Blue solution
[Fe(H2O)6]2+
Pale green solution
[Mn(H2O)6]2+
Pale pink solution
+ NaOH
+ excess NaOH
Cu(H2O)4(OH)2
Dropwise NH3
Cu(H2O)4(OH)2
Blue precipitate
Blue precipitate
Fe(H2O)4(OH)2
[Fe(H2O)4(OH)2
Green precipitate
(if left standing
turns orange
brown).
Green precipitate
(if left standing
turns orange
brown).
Mn(H2O)4(OH)2
Mn(H2O)4(OH)2
Pale brown
precipitate
Pale brown
precipitate
Fe(H2O)3(OH)3
Fe(H2O)3(OH)3
Excess NH3
[Cu(H2O)2(NH3)4]2+
Deep (royal) blue
solution
[Cr(H2O)6]3+
Violet solution
Orange-brown
precipitate
[CuCl4]2Yellow solution
[FeCl4]2-
[Fe(H2O)6]3+
Pale yellow solution
Excess HCl/NaCl
[FeCl4]-
Orange-brown
precipitate
Cu(H2O)3(OH)3
[Cr(OH)6]3-
Cr(H2O)3(OH)3
[Cr(NH3)6]3+
Green precipitate
Dark green solution
Green precipitate
Purple solution
Last 3 years of OCR
Transition Metal
Questions
2021
• Ligand substitution of an octahedral complex with 2
bidentate ligands and then drawing the 3 stereoisomers • Variable oxidation states of copper
• What is a transition metal and what is and isn’t a
transition metal with electron configs
2020
2019
Predicted Questions for June 2022
•
Reactions involving aqueous Cu2+
•
Very little on qualitative analysis so maybe a flow chart with a variety of
the reactions from the table
•
Cisplatin and the action of it
•
Questions involving some unfamiliar bidentate ligands
•
Interconversions between Fe2+ and Fe3+
•
Explanation of the biochemical importance of iron in haemoglobin,
including ligand substitution involving O2 and CO