Transition metals Flashcards
what is a transition metal
element that has an incomplete d sub-shell in either its atoms or one of its common ions
Properties of transition metals
the incomplete d sub-shell is responsable for a number of general properties of the transition metal elements :
- variable oxidation states
- catalytic action
- coloured compounds
- formation of complexes
D- block element
are elements that have their outer most electrons in a d-orbital
Why is Zn not a transition metal?
Zn can only form a +2 ion. In this ion the Zn2+ has a complete d orbital and so does not meet the criteria of having an incomplete d orbital in one of its compounds.
Why is Sc not a transition metal?
Sc can only form a +3 ion. In this ion Sc3+ has an empty d orbital and so doesn’t meet the criteria of having an incomplete d orbial in one of its ions
What is the coordination number?
The of dative covalent bonds formed with the central metal ion
Example Q
Give the Electron configuration for Cr element
1s2 2s2 2p6 3s2 3p6 4s1 3d5
When doing electron configuration of ions, which electrons do you remove first in a + ion
The 4s orbital ions
Ligand substitution
What is a ligand?
- A ligand is an atom/ion/molecule that donates a pair of electrons to a central metal atom/ion.
- Needs at least one lone pair of electrons
- Otherwise it cannot form a dative covalent bond
Ligand substitution
What is a ligand with one lone pair called?
what examples ?
Monodentate (H2O, NH3, Cl-, OH-)
Ligand substitution
What is a ligand with two lone pairs called?
what examples ?
Bidentate e.g. 1,2-diaminoethane
Ligand substitution
Ligand with more than two lone pairs?
what examples ?
Multidentate e.g. EDTA4- (6 lone pairs) can form 6 dative bonds
Ligand substitution
What affects the size of the energy gap when ligands are bonded to metal ions?
Which central metal ion it is, its oxidation number, which ligands they are and the coordination number
Complexes
What are complex ions?
A complex ion is a metal ion surrounded by dative covalently bonded ligands
Complexes
What gives the distinctive shapes of complex ions?
The bonding electrons in the dative covalent bonds of a complex repel each other.
This means that they will try to get as far away as possible.
Causing complexes with different coordination numbers to have distinctive shapes.
complexes
Which ligand can only form 4 coordinate bonds?
Cl
what is the chelate effect ?
The replacement of monodentate ligands with bidentate and multidentate ligands in complex ions
It is an energetically favourable reaction, meaning that ΔGꝋ is negative
The driving force behind the reaction is entropy
complexes
Haemoglobin contains ___ ions
Fe2+
complexes
Haemoglobin forms an ____ shape
octahedral
Complexes
Haem
A square planar ligand attached to a ferrous group
Complexes
Globin
A complex protein molecule attached to a ferrous group from below
Complexes
Which complex ion can only form 2 coordinate bonds?
Ag
Example Q
why is CO toxic ?
Carbon monoxide is toxic because it is a better ligand than oxygen and binds strongly and irreversibly to the iron(II) preventing oxygen from being carried to the cells
complexes
what is Ethanedioate ?
4
- A bidentate ligand that has two negative charges
- C2O2−4
- colourless
- naturally occuring in some food
Example Q
Ethanedioate ions are poisonous because they react with iron ions in the body.
Ethanedioate ions are present in foods such as broccoli and spinach.
Suggest one reason why people who eat these foods do not suffer from poisoning.
The ethanedioic acid is only present in small quantities / low concentration in these foods.
Chelates
Complex ions with polydentate ligands attached, which can be used to remove d-block elements from a solution
Complexes
what is the haem complex?
- The haem molecule is a complex with iron(II) at its centre
- Oxygen atoms form a dative covalent bond with the Fe(II) which enables oxygen molecules to be transported around the body in the blood
- Oxygen molecules are not very good ligands and bond weakly to the iron(II). The weak bonds allows them to break off easily and be transported into cells
complexes
Unidentate examples
NH3, H20, Cl-, OH-
complexes
What is Diaminoethane ?
4
- A bidentate ligand that has no charge
- C2H4(NH2)2
- colorless liquid with an ammonia-like odor
- is used as a building block for the production of many other chemical products
Why do multidentate ligands substitute unidentate?
No difference in ethalpy, but entropy increases, as there is more disorder
What is a ligand substitution reaction?
- Ligand exchange (or ligand substitution) is when one ligand in a complex is replaced by another
- Ligand exchange forms a new complex that is more stable than the original one
what happens in a ligand substitution reaction if both ligands are of similar size?
There are no changes in coordination number, or the geometry of the complex
What happens in a ligand substitution reaction when the ligands are of different sizes?
for example water ligands and chloride ligands, then a change in coordination number and the geometry of the complex will occur
When does incomplete Ligand Substitution takes place ?
- if the energetics of the reaction and stability of the product are not favourable
- Copper(II)ions illustrate this behaviour with ammonia
- Different sized ligands can also lead to incomplete substitution
what isomerism do octahedral complexes show ?
optical isomerism
Cisplatin
- is the cis isomer of the square planar complex of platinum
Colorimetry
- the strength of absorption of a rage of solutions of known concentration is measured and a graph is produced
- the more concentrated the solution the higher the absorbency
- concentration of a solution of unknown concentration can be found by measuring the absorption and using the graph
Explain how a calibration graph is produced and used to find the concentration of complex
M1 measure absorbance for (a range of) known concentrations
M2 plot graph absorbance v concentration
Allow concentration v absorbance
M3 read value of concentration for the measured absorbance from this graph
If no M1, must mention both variables
Need to describe HOW they use the graph
Example Q
Give the equation for the reaction between iron and sulfuric acid.
Fe (s)+H2SO4(aq)→ FeSO4(aq)+H2(g)
Example Q
Give the overall ionic equation for the oxidation of Fe2+ by manganate(VII) ions, in acidic conditions.
MnO4- (aq) + 8H+ (aq) + 5Fe2+ → Mn2+ (aq) + 5Fe3+ (aq) + 4H2O (l)
Example Q
State why an indicator is not added in this titration using potassium manganate(VIl) solution.
Potassium permanganate itself acts as a self-indicator.
Example Q
Ethanedioate ions react with aqueous iron(Ill) ions in a ligand substitution reaction.
Write an equation for this reaction.
Suggest why the value of the enthalpy change for this reaction is close to zero.
[Fe(H2O)6] 3+ + 3C2O4 2− → [Fe(C2O4)3] 3− + 6H2O
Same number and type of bond being broken and made.
