Learning Objectives Flashcards
What is a transition metal?
d-block elements that can form one or more stable ions with partially filled d-orbitals
Why are Sc and Zn not transition metals?
Sc will form a stable ion that has no electrons in the d subshell, and Zn will form a 2+ ion that will have a full d subshell
Why do transition metals show variable oxidation numbers?
Successive ionisation energies of transition metals are similar because 4s and 3d orbitals are very close in energy levels
What is a ligand?
A species with at least one lone pair that is able to form coordinate bonds with metal ions
What is a complex ion?
A central metal ion surrounded by ligands
What is the coordination number?
The amount of co-ordinate (dative) bonds existing in the complex ion
What kind of bonding is present in a complex ion?
Co-ordinate (dative) bonds existing
When will a transition metals show a colour?
Transitions metals form coloured ions in solution
What impacts the colour of a transition metal?
The energy gap (change in E) which is dependent on
a. Central transition metal ion surrounded
b. Charge of the transition metal ion
c. Ligands
d. Coordination number of the complex
A AND B CHANGE THE ELECTRON CONFIG
What causes the colour of transition metals?
When ligands bond to a central metal ion, they change the energies of the d orbitals - leading to some gaining energy and some losing energy (splitting of orbitals)
The difference in energy levels determines the colours of light that are absorbed (the one that is reflected is the one that it looks like)
Why are some ions not coloured?
If their d orbitals are full or empty (Sc and Zn) then electrons cannot move between the energy levels so not light can be absorbed and no colour is seen
Why are H2O, OH- and NH3 monodentate ligands?
They all have one lone pair that can be donated to the central metal ion - in H2O’s case, it has two lone pairs, but only one is readily available for donation
What shape and angle do six-fold complexes have?
Octahedral and 90
Why are six-fold complexes an octahedral shape?
Similar to bonding in shapes, the electron pairs want to maximise separation and minuses repulsion
If a complex is four-fold, what shapes and respective angles can it make?
Tetrahedral and 109.5, or, Square planar and 90 and 180
What is an example of a ligand that forms a 2-fold complex?
Ag+
What is an example of a ligand that forms 4-fold (tetrahedral) shapes?
Cl- and CN-
What is an example of a ligand that forms 6-fold complexes?
Most things tbh, e.g. H2O, NH3 AND OH-
What is an example of a ligand that forms a 4-fold (square planar) complex?
Pt, Ni, Pd
Why does Cl- form four fold complexes?
It is relatively large so many of them cannot fit around a central metal ion
What does cisplatin look like?
Square planar (2 Cl ligands and 2 NH3 ligands surrounding a Pt central metal ion)
How is cisplatin different from transplatin structurally?
Cisplatin shows CIS (same) isomerism meaning both the Cl ligands are adjacent to each other.
Transplatin shows TRANS (across) isomerism so the Cl ligands are opposite to each other.
How is cisplatin used as a cancer treatment? And why is transplatin not used in the same way?
Cisplatin contains 2 (not very good) Cl ligands that can undergo ligand substitution when a better ligand comes around, like something containing Nitrogen (nitrogenous bases but specifically guanine)
This allows cisplatin to STOP DNA synthesis as it can lose the 2 Cl ligands to form co-ordinate bonds with 2 guanines next to each other on the chain instead.
This then prevents the enzyme, DNA polymerase, from connecting the bases so replication is halted
Transplatin cannot do this because it only has 1 Cl ligand that is able to be substituted at one time and the ONE co-ordinate bond between transplatin and the base is not enough to stop DNA polymerase
What are the bidentate ligands you need to know?
1,2-diaminoethane (NH2CH2CH2NH2)
Ethanedioate (C2O4)
What are the multidentate ligands you need to know?
EDTA 4-
- it has four letters so have a charge of 4
- it’s negative bc it’s a ligand and the central metal ion is always positive
What is a specific example of a complex ion in the blood?
Haemoglobin is an iron(ii) complex
Oxygen is usually co-ordinately bonded with haemoglobin, what ligand can do a ligand exchange reaction and prove fatal?
Oxygen is transported around the body by haemoglobin by forming co-ordinate bonds with the Fe2+ ion
Carbon monoxide will irreversibly bind to the Fe2+ ion and prevent oxygen from binding - carbon monoxide poisoning
What are is the pneumonic for Vanadium’s colours in order of descending oxidation state?
You Better Get Vanadium
Yellow Blue Green Violet
What reaction changes vanadium’s oxidation states?
Reduction reactions including Zn in acidic conditions
What is the relevance of E values for the interconversion of the oxidation states of vanadium?
The E values indicate the tendency of vanadium in a specific oxidation state to be reduced.
As the oxidation states lower, the E value lowers meaning the reaction are less feasible - higher oxidation states leads to more stability
They can help with predicting what oxidation state vanadium will have and if a reaction will even occur
In redox reactions, how can you tell which one is the oxidising agent and which one is the reducing agent based on oxidation states?
High oxidation states usually are oxidising agents (get reduced)
Low oxidation states are usually reducing agents (get oxidised)
How can dichromate ions be converted into chromate ions and vice versa?
Through the equilibrium
2CrO₄²⁻ + 2H⁺ ⇌ Cr₂O₇²⁻ + H₂O
Add either acid or alkali
Acid - more Cr₂O₇²⁻
Alkali - more CrO₄²⁻
What reactions do transition metals undergo and describe them
Ligand exchange/substitution
- a better ligand will form a stronger bond with the central metal ion so kicks another worse ligand off
Redox
- oxidation stars of transition metal changes
Acid-base
- ligands lose or gain H+
When does ligand exchange occur?
- A better ligand is available
- A change in pH in aqueous solution
- A change in coordination number
- complex ion is introduced to high conc of alternative ligand
What is the chelate effect?
Exchange of monodentate or bidentate ligands to multidentate ligands producing more aqueous species to increase entropy so reaction is thermodynamically favourable and a more stable complex ion is produced
If a transition metals undergo ion is not a polyatomic ion, it is assumed to be…
complexed to 6 water collectors in aqueous solution
What is the optimal conditions for chromate and dichromate?
Chromate is more stable in alkaline
Dichromate is more stable in acidic
What is the optimal conditions for chromate and dichromate?
Chromate is more stable in alkaline
Dichromate is more stable in acidic
What does amphoteric mean?
A substance that can behave as an acid or a base
