Transition Metals Flashcards
What are d block elements
their highest energy electrons are in the d orbital
What are transition metals
An element which forms at least one stable ion with a partially full d-shell of electrons
What are the characteristics of transition metals
- form complexes
- form coloured ions
- variable oxidation states (they have partially filled d orbitals so can lose 4s and 3d electrons)
- catalytic activity
Why is zinc not a transition metal
It can only form a 2+ ion. In this ion the Zn2+ has a complete d orbital
What is a complex
A central metal ion surrounded by ligands
What is a ligand
An atom, ion or molecule which can donate a lone electron pair to form a dative covalent bond
What is the coordination number
The number of dative covalent bonds a ion is forming
Explain why complexes formed from transition metal ions are coloured
- some wavelengths of light are absorbed
- to promote electrons in the d orbitals to higher energy levels
- the light that is not absorbed is transmitted to give the substance colour
AE = ?
- plancks constant x frequency of light absorbed
- plancks constant x speed of light/wavelength of light absorbed
Give 3 examples of catalysts and the reactions they catalyse
Iron - Haber process
Vanadium (V) oxide - contact process
MnO2 - decomposition of H2O2
Which electrons do transition metals lose first when forming ions
4s
How many coordinate bonds does EDTA form
6
When a compound is dissolved in water what shape does it form
Octahedral with 6 H20 Ligands
Explain the chelate effect in terms of entropy
- multidentate ligands = more molecules
- so significant increase in entropy
- delta G is less than 0
- so reaction is feasible
- more stable complex ion formed
What shape is Platin
Square planar - forms Cisplatin
How does haemoglobin transport oxygen
Oxygen forms a coordinate bond to Fe(II) in haemoglobin, allowing it to be transported in the blood
Why is carbon monoxide toxic
It replaces oxygen coordinately bonded to Fe (II) in haemoglobin
What is the chelate effect
Bidendate and multidentate ligands replace monodentate ligands from complexes
How would changing a ligand or coordination number change colour
It will alter the energy split between the d orbitals, changing AE and the frequency of light absorbed
What can be used to reduce Vanadium
Zinc
What colour is MnO4-
Deep purple
What colour is Mn2+
Pink
What colour is Cr2O7 2-
Orange
What colour is Cr3+
Green
What colour is Fe2+ aqua ion
Green
What colour is Fe3+ aqua ion
Pale brown
What colour is Cr2+ aqua ion
Blue
What colour is Cr3+ aqua ion
Red/violet
What colour is Co2+ aqua ion
Brown
What colour is Co3+ aqua ion
Yellow
Why are transition metals good catalysts
They can exist in variable oxidation states so can provide alternative pathways easily
What are the 2 equations for vanadium catalyst in the contact process
SO2 + V2O5 —> SO3 + V2O4
2V2O4 + O2 —> 2V2O5
Describe how a heterogeneous catalyst works
- the reactants adsorb onto the surface/active sites
- the bonds weaken and reaction takes place
- the products desorb from the surface
Describe how to obtain a calibration graph
- measure absorbance for a range of known concentrations
- plot a graph of absorbance vs concentration
- read the value of concentration for the measured absorbance from the graph
Explain why a compound may be white
- full 3d subshell
- so can’t absorb visible light
Why might the enthalpy change/AH for a reaction be (almost) 0
Same number and type of bond being broken and made
Define autocatalysis
When the product of a reaction is also a catalyst for that reaction
Write two equations to show how Fe2+ catalyses the reaction between S2O8(2-) ions and I- ions
S2O8 (2-) + 2Fe2+ —> 2Fe3+ + 2SO4 (2-)
2 Fe3+ +2I- —> 2Fe2+ + I2
Define homogenous vs heterogenous catalyst
Homogeneous catalyst is in the same phase as reactants
Heterogeneous catalyst is in a different phase from the reactions
What is a Lewis acid and base
Acid - electron pair acceptor
Base - electron pair donor
What colour is V3+
Green
What colour is V2+
Violet
What colour and oxidation state is VO2 (+)
5+
Yellow
What colour and oxidation state is VO (2+)
4+
Blue
How could a compound increase the pH
- has a high charge density
- so polarise water molecules more
- so weakens the OH bond in water, releasing H+ ions
What are the monodentate ligands
H20, NH3 and Cl-
If CuCl2 solid is dissolved in solution what is its Ligand
[Cu(H20)6] 2+
What are the two bidentate ligands
- Ethane-1,2-diamine
NH2CH2CH2NH2 - Ethanedioate
C2O4 (2-)
Both form 2 coordinate bonds
What is the multidentate ligand called
EDTA (4-)
Forms 6 coordinate bonds
Explain Cl- effect on the coordination number when it reacts
It decreases eg from 6 to 4
Because Cl- ions are larger so only 4 can fit around the metal ion
What is Cis-trans isomerism
Occurs in monodentate Ligands
E-Z isomerism
Trans - E
Cis- Z
What type of isomerism occurs in bidentate ligands
Optical isomerism
Describe why optical isomerism occurs
The arrangement of the coordinate bonds can lead to enantiomers formed
What two factors effect the lifetime of a catalyst
- catalyst poisoning - active sites blocked
+ large surface area eg by using powder or small pellets
Describe a ligand reaction in Gibbs terms in which the no. Of molecules increases
- increase in entropy as more moles of products than reactants
- so more disorder
- delta S is positive
- delta G is negative so reaction is feasible (write equation to work out AG)
- delta H is close to 0 because same number and type of of bonds
Why might a reaction be slow before a catalyst is added
If there are two negative ions that repel
It will make the activation energy higher
Why might a ion not be able to catalyse a reaction
- doesn’t have a variable oxidation state
Why might two atoms be a good catalyst
Because the two oppositely charged ions attract each other
