Transition metals Flashcards
Define transition metals
Metals that can form 1/more stable ions w/ partially filled d sub-shells
What causes the special chemical properties of T-metals?
Incomplete d sub-shell
Why is scandium not a t-metal?
- Only forms 1 ion: Sc3+
- Empty d sub-level
Why is zinc not a t-metal?
- Only forms 1 ion: Zn2+
- Has full d sub-level
When ions are formed which e- are removed first?
S then D
State the physical properties of t-metals
- High density
- High MP + BP
- Ionic radii = same
State the chemical properties of t-metals
- Form complex ions
- Form coloured ions
- Good catalyst
- Variable oxidation state
Why do t-metals show variable oxidation states?
- Energy level of 4s + 3d sub-level are v close to one another
- So diff. no. e- gained or lost using similar amounts of energy
Cu2+
Blue
Ni2+
Green
Co2+
Pink
Fe2+
Pale green
Mn2+
Pink
V2+
Violet
Fe3+
Yellow
Cr3+
Green/violet
V3+
Green
VO2+
Blue
VO2+
Yellow
Cr2O72+
Orange
MnO4-
Purple
Define complex
Central metal atom/ion surrounded by co-ordinately bonded ligands
Define co-ordinate bond
Covelant bond where both e- in shared pair come from same atom/ligand
Define ligand
Atom, ion or molecule that donates pair of e- to central t-metal to form co-ordinate bond
Define co-ordinate no.
No. of co-ordinate bonds formed w/ central metal ion
Which ligands do t-metals form octahedral complexes w/?
- Small ligands
- Eg. H2O, NH3
Which ligands do t-metals form tetrahedral complexes w/?
- Larger ligands
- eg. Cl-
What shape does 6 co-ordinate bonds form + what is the bond angle?
- Octahedral
- 90º
What shapes do 4 co-ordinate bonds form + what is the bond angle?
- Tetrahedral: 109.5º
- Square planar: 90º (cisplatin)
What shape does some silver complexes w/ 2 co-ordinate bonds form + what is the bond angle?
- Linear
- 180º
What is the overall charge on the complex ion?
Total oxidation state
Oxidation state of metal ion equation
Oxidation state of metal ion = total oxidation state - sum of oxidation states of ligands
Give an example of a linear complex + what it’s used for
- [Ag(NH3)2]+
- Tollen’s reagent
Define monodentate
Give examples
Ligand that can only form 1 co-ordinate bond
H2O, NH3, Cl-
Define multidentate
Give examples
Ligand that can form more than 1 co-ordinate bond
EDTA4-
What does EDTA4- stand for?
ethane diomine tetra acetate
Define bidentate
Give examples
Multidentate ligands that form 2 co-ordinate bonds
- ethane-1,2-diamine (H2NCH2CH2NH2)
- ethandioate (C2O42-)
What is haem?
Iron (II) complex w/ multidentate ligand
Why is haemoglobin important?
O2 co-ordinately bonds to Fe2+ to form oxyhaemoglobin + is carries O2 round body in blood
Why is CO dangerous?
- Co-ordinately bonds to Fe2+ instead of O2, forming carboxyhaemoglobin
- CO is a strong ligand + doesn’t readily exchange w/ H2O/O2 ligands
- Unable to transport O2 round body
- Causes: headaches, dizziness + death
Define optical isomerism
Ions can exist in 2 forms that are non-superimposable mirror images
Which complexes show optical isomerism?
Octahedral complexes w/ bidentate ligands
Which complexes form + display cis-trans isomerism?
- Octahedral complexes (monodentate ligand)
- Square planar
What is the cis isomer of cisplatin used for?
Anti-cancer drugs
When does the 3d orbital split into 2 diff energy levels?
Ligands bond to ions + causes orbitals to gain energy
Which orbitals do e- tend to occupy?
Lower orbitals
Where does e- get energy from to jump up to the higher orbitals?
Visible light
What happens when visible light hits a t-metal ion?
d e- move from ground state to excited state
How does colour arise in t-metals?
- Some wavelengths of visible light are absorbed
- Rest of freq. transmitted/reflected
What does the freq. absorbed depend on?
Size of the energy gap ΔE
What happens when the frequencies are reflected/transmitted?
Freq combines to make compliment of colour of absorbed freq - colour you see
What is the colour when there are no 3d e- or 3d sub-level is full?
- Colourless
- Bc no e- will jump so no energy absorbed
The larger the gap the___ the feq. of light that is absorbed
Higher
How can the colour of a complex be altered?
By change size of energy gap
- Change in:
- Oxidation state
- Co-ordination no.
- Ligand
What can be used to find the conc of t-metal ions?
- Spectroscopy
- White light shone through filter, chosen to only let colour of light absorbed by sample
- Light passes through sample to colorimeter - calculates how much light is absorbed
- More conc = more light absorbed
What must be produced before finding the unknown conc of a sample?
- Calibration curve - measuring absorbance of known conc of solutions + plot on graph
- Measure absorbance of sample + read off graph
Define ligand substitution
What does it usually result in?
- Ligands changing places w/ another
- Colour change
What happens to the co-ordination no. + shape of a complex ion if the ligands are similar size + same charge?
Nothing
Why is substitution btw H2O + NH3 easy?
- Similar size
- Both uncharged
What happens to the co-ordination no. + shape of a complex ion if the ligands are diff. size?
Changes
Why is the enthalpy change for a ligand exchange reaction v small?
Strength of bonds being broken is v similar to bonds formed
What is the chelate effect?
When monodentate ligands are substituted w/ bidentate + multidentate ligands, inc in stability, no. particles inc, so greater entropy - more likely to occur
What is used to reduce vanadium ions?
Zinc metal in acidic solution
How is the stability of an ion affected the larger the redox potential?
Less stable, more likely to be reduced
How is the redox potential affected in an acidic solution?
Larger redox potential, easier to reduce
Outline how to carry out a titration to find out how much oxidising agent is needed to react w/ a quantity of reducing agent
- Measure out reducing agent using pipette + put into CF
- Using measuring cylinder, add dliute sulfuric acid to flask
- Add oxidising agent (aqueous potassium manganate) to reducing agent using burette
- Add until the mixture changes colour to purple
How do transition metals work as catalysts?
Changing oxidation states
Outline heterogeneous catalyst
- Diff phase to reactants
- Reaction happens at active site on surface of catalyst
- Support mediums used to max. SA + minimise cost
Give examples when heterogenous catalysts are used
- Iron in haber process to make ammonia
- Vanadium oxide in contact process to make sulfuric acid
What is the problem in using hetrogenous catalysts?
Give example
- Impurities bind to catalyst surface + block reactants from being adsorbed - catalyst poisoning
- Reduces SA, slowing down reaction
- Inc cost
- Sulfur poisons iron catalyst in haber process, H produced from methane, sulfur reacts w/ iron to produce iron sulfide
Outline the process of heterogenous catalyst
- Diffusion
- Adsorption
- React (bonds broken/formed)
- Desorption
- Diffusion
Outline homogneous catalyst
- Same phase as reactants
- Work by forming intermediate species which react to form products + re-form catalyst
Why is the reaction btw iodide ions + peroxidisulfate slow?
How can you over come this problem?
- Both ions -ve charged so repel, less likely to collide
- Add Fe2+ ions bc +ve ion so no repulsion
Define autocatalyst
Product of reaction catalyses reaction
