Transition metals Flashcards
What is special about scandium and zinc
They are not transition metals as their ions have either full or empty d oribtals
What is a transition element?
A d block element that forms at least 1 ion with an incomplete d sub shell
What is a complex ion
A central metal atom or ion surrounded by ligands.
What is a ligand?
A molecule or ion that can donate a pair of electrons to the transition to form a dative bond
What is the number of co-ordinate bonds called
The coordination number
What does monodentae mean
A ligand donates 1 pair of electrons to form 1 co-ordinate bonds
What is the convention for writing the chemical formula of a complex ion
Overall charge is outside the brackets
All the charges in the bracket must add to the outside bracket
[Co(H2O)5Cl]+
5 water ligands - no charge
Cl = -1
Therefore Co = 2+
What are the 4 characteristic properties of transition elements
Complex formation
Formation of coloured ions
Variable oxidation states
Catalytic activity
What are 3 examples of monodentae ligands
H2O
NH3
Cl-
In what way are the ligands NH3 and H2O similar
They are similar sizes
Both have no charge
Why doesnt the co-ordination number change when H2O is substituted with NH3
They are similar sizes
Can their only be 1 type of ligand on a molecule
No it can be incomplete
e.g. [Cu(NH3)4(H2O)2]2+
How big is the Cl- ligand compared to NH3 and H2O
It is larger
Can Cl- replacing H2O ligand change co-ordination number
Yes it can
What is a bidentae ligand
3 examples?
2 dative covalent bonds
e.g. ethane-1,2-diamine/
benzene-1,2-diol
Ethane dioate (C2O4)2-
What is an example of a multidentae ligand
EDTA 4-
What is Haem
An iron 2 complex with a multidentae ligand
How does oxygen attach to haem
it forms a co-ordinate bond with the Fe (II) enabling it to be transported in the blood)
Why is CO toxic
It replaces the oxygen co-ordinate bond
What is the chelate effect
A multidentae ligand is favourable to monodentae ligands
Why is the chelate effect true
EDTA 4- + [Cr(H2O)6]3+ —> [Cr(EDTA)]- + 6H2O
3en + [Cr(H2O)6]3+ —> [Cr(en)3]3+ + 6H2O
The multidentae ligand starts with 2 molecules on the left and 7 on the right. There has been a large change in entropy towards chaos which the universe favours
The 3 bidentae ligands start with 4 molecules on the left and 7 on the right. The entropy change in less
Enthalpy change is negligible
What is a common complex shape formed between small ligands and metal ions
An octahedral complex
What types of isomerism can octahedral complexes display
Cis-Trans isomerism with monodentae ligands
Optical isomerism with bidentae ligands
What type of complex is formed between larger ligands and metal ions
Tetrahedral complexes (Cl-)
Square planar complexes (can display cis trans isomerism)
What shape is cis platin and which isomer is it
Square planar
Cis isomer
What shape does Ag+ form
A linear complex
What is [Ag(NH3)2]+ used for
Tollens reagent
What is the formula for tollens reagent
[Ag(NH3)2]+
What are the requirements for an optical isomer
3 bidentae ligands
2 bidentae ligands & 2 monodentae ligands
1 hexandentae ligands
How can transition metal oxide be identified
By their colour
How does colour arise from transitions metals
Some of the visible light is absorbed and the remaining wave lengths of light are reflected
D electrons move from the ground state to an excited state when light is absorbed
What is the formula for the energy difference between the ground state of electrons and their excited state
ΔΕ = hv
h= planks constant v= frequency
ΔΕ = hc/λ
h= planks constant c= speed of light λ= wave length (m)
What 3 things can lead to a change in colour of a metal compound
Oxidation state
Co-ordination number
Change in ligand
What is the absorption of visible light used in
Calorimetry
What can a colorimeter be used for
Determining the conc. of coloured ions in solution
What are the redox equations for the reduction of vanadate ions by zinc in acidic solutions
Zn —> Zn2+ + 2e-
VO2^+ + 2H+ +e- —> VO^2+ + H2O
2VO2^+ + 4H+ + Zn —> 2VO^2+ + 2H2O + Zn+
C2O4 2- + MnO4- redox
C2O4 2- —> 2CO2 + 2e-
MnO4- + 5e- + 8H+ —> Mn2+ + 4H2O
5C2O42- + 2MnO4- + 16H+ —> 10CO2 + 2Mn2+ + 8H2O
When does a transition metals oxidation state increase
In an alkaline solution
Why do transition metals oxidation states increase in alkaline solution
Since oxidation is electron loss, it is easier to form negatively charged ions than a neutral or positive one
How can low oxidation states be stabilised
Keep them in an acidic solution
Fe2+ + MnO4- redox reaction
Fe2+ —> Fe3+ + e-
MnO4- + 5e- + 8H+ —> Mn2+ + 4H2O
5Fe2+ + MnO4- + 8H+ —> 5Fe3+ + Mn2+ + 4H2O
What type of catalysts do transition metals act as
Heterogenous catalysts
Homogenous catalysts
What is a heterogeneous catalyst?
A catalyst in a different phase from the reactants and the reaction occurs at the active sites in the surface
What can be used to increase S.A of a heterogenous catalyst and reduce cost
Use a support medium
e.g. honey comb structure coated in platinum in catalytic converters
What is the heterogenous catalyst used in the contact process
V2O5
What is the heterogenous catalyst used in the haber process
Fe
Will heterogenous catalysts last forever
No, they can become poisoned by impurities that block active sites.
This reduces efficiency which will cost the company
Platinum acts as a heterogeneous catalyst in the reaction between ammonia and oxygen. It provides an alternative reaction route with a lower activation energy.
Describe the stages of this alternative route
Reactant(s) adsorbed onto the platinum active sites
Reaction (on the surface) or bond breaking (weakening) / bond making occurs (on the surface)
Desorption (of the product)
What is a homogenous catalyst
Same phase as the reactants
How do homogeneous catalysts work
The reaction proceeds through an intermediate species
Why are variable oxidation states important in catalysis
Transition metals can adopt more than 1 stable oxidation state
This means they can gain and lose electrons and remain stable
Therefore they can act as both an oxidising and reducing agent in a redox reaction
What is the contact process
2SO2 + O2 —> 2SO3
What are the equations for the contact process with a V2O5 catalyst
SO2 + V2O5 —> SO3 + V2O4
2V2O4 + O2 —> 2V2O5
How does Fe2+ catalyse the reaction between I- and S2O82-
(Overall and sub equation)
S2O8 2- + 2I- —> 2SO4 2- + I2
S2O8 2- + 2Fe2+- —> 2SO4 2- + 2Fe3+
2Fe3+ + 2I- —> 2Fe2+ + I2
Explain what happens during autocatalysis
The reaction starts of slow as not much of the product (catalyst) has been formed yet
The reaction then speeds up quickly
It then slows down again at the end
A calculation of the enthalpy of lattice formation of silver iodide based on a perfect ionic model gives a smaller numerical value than the value calculated in Question 1.2
Shows covalent character
Forces holding the lattice together are stronger
