Transition Metals and their Chemistry Flashcards
What is a simple definition of a transition metal?
An element between the s and p blocks of the periodic table
What is a better definition of a transition metal?
An element which forms one or more stable ions which have incompletely full d sub-shells
What are the general properties of transition metals?
Hard metals with high melting and boiling temperatures
Show more than one oxidation number in their compounds
Many show catalytic activity
Which are d block elements that are not transition metals?
Scandium and zinc
Second definition excludes them
Where are the first electrons lost from in transition metals?
Outer 4s subshell followed by the 3d subshell
How are the small fluctuations in the general trend of increasing ionisation energies explained?
Relative stability of full and half-full subshells
What can phytomining be used for?
Extract transition metals using plants from areas where they cannot be obtained economically by other methods
How is phytomining carried out?
Crops grow on soil containing metal
Plant is burned and energy used for electricity
Leaves bio-ore which is then smelted
What are the advantages and disadvantages of phytomining?
Bio-ores are almost sulphur free
Need less energy for smelting
Cause less acid rain pollution
Usually have higher metal content than mineral ores
‘Green’ alternative to mining low grade ores
Only commercially viable if the price of the metal being extracted remains high
What are general observations made on the transition metals from titanium to copper?
+1, +2, +3 are the most common
From titanium to chromium, +3 is the most common
From manganese onwards, +2 is the most common
What happens with very high oxidation numbers?
Involved in covalent bonding Mn2O7
Form polyatomic ions such as (CrO4)2-
What does changes in the colour of solution indicate?
A change in the oxidation number of the ion
When the 3d orbital is either empty of full, the solution is colurless
What is a simple explanation for explaining the colour of solution?
Due to electrons absorbing photons of certain frequencies of visible light
Energy of each of these photons matches the energy needed for one electron to jump from a lower to a higher energy orbital
Frequencies of visible light remaining after this absorption give the solution its colour
What sort of bonding is involved in complex ions?
Dative covalent (co-odinate) bonds
How are complex ions formed?
Small size results in high electron density which attract electron rich species
Central metal ion is surrounded by either anions or molecules that act as electron-pair donors
The electron-pair donors are called ligands
What does the number of ligands involved in a complex ion depend one?
Size of metal ion
Size of ligand
What is the charge of a complex ion?
Sum of the charge on the metal ion and the charge(s) of the ligands
What are anionic and cationic ion complexes?
Anionic - Attracted to anode during electrolysis
What is the co-ordination number?
Number of lone pairs attached to the metal ion
What are monodentate, bidentate and polydentate ligands?
Mono - join to the metal ion by one atom only
Bi - join to the metal atom by two atoms
Poly - attach to the metal ion by more than two atoms
What is 1,2-diaminoethane? Where are the lone pairs?
:NH2-CH2-CH2-H2N:
What is ethanedioate? Where are the lone pairs?
:O- :O-
C - C
=O =O
What is the charge of edta? Where are the lone pairs?
4-
Nitrogen and oxygens with single bonds
6 lone pairs
Give 3 biological examples that contain transition metals?
Chlorophyll, vitamin B12 and haemoglobin
What does the shape of complex ions depend on? Give some examples of sorts of shape
Depends on number of electrons within the d orbital and the coordination number
Linear, planar, tetrahedral, octohedral
What is the most common coordination number and what shape is it?
6
Octohedral
What are the oxidation numbers of vandium? What are the colours?
V2+ +2 Purple
V3+ +3 Green
(VO)2+ +4 Blue
(VO2)+ +5 Yellow
What must be taken into account when working out a suitable reducing agent?
The reaction involving the vandium species must have a more a more positive E standard (so it goes to the right) than the E standard of the reducing agent
Activation energy and kinetic feasibility must also be taken into account
What does the stability of oxidation numbers depend on?
Arrangement of electron in the ions
Half-full of full subshells are more stable
How does copper (I) exist?
Unstable in aqueous solution
Exists at high temperatures, when insoluble and precipitated, in complexes
How do copper (I) compounds disproportionate in aqueous solution?
Cu2SO4 –> Cu(s) + CuSO4(aq)
How can copper (I) ions be stabilised in solution?
Adding conc HCl to form a complex
CuCl(s) + Cl-(aq) –> [CuCl2]- (aq)
How can copper (I) chloride be made?
Boil: [Cu(H2O)6]2+ +4Cl- –>[CuCl4]2- +6H2O
Boil: [CuCl4]2- + Cu(s) –> 2[CuCl2]-
[CuCl2]- + (cold water) –> CuCl(s) + Cl-
How is copper (I) iodide made?
Precipitated as a white solid when potassium iodide solution is added to copper (II) sulphate solution
How is copper (I) oxide made?
Precipitated as a red solid when alkaline solution of copper (II) sulphade is reduced be glucose?aldehyde
Cu2+ complexed with 2,3-dihydroxybutanedioates to prevent precipitation of Cu(OH)2
What are the oxidation number and colour of chromium (II)?
Cr2+ pale blue in aqueous solution
Easily oxidised
What is the most stable oxidation number of chromium?
Cr3+ violet/blue-grey
Hydrated gives green solution when involved in reactions as a ligand exhange often takes place
Exhibits amphoteric characteristics
[Cr(H2O)3(OH)3] + 3H+ –> [Cr(H2O)6]3+
[Cr(H2O)3(OH)3] + 3OH- –> [Cr(OH)6]3- +3H2O
What are chromium compounds often used as?
Green and yellow pigments, protective primers, tanning animal hides and to prevent the corrosion of metals
What is the highest oxidation number of chromium and what are the colours of its compounds?
+6
CrO3
Chromate ion (CrO4)2- bright yellow
Dichromate (Cr2O7)2- orange
How does chromium oxide react with water?
CrO3(s) + H2O –> H2CrO4(aq)
How does the chromate (VI) and the dichromate (VI) ion exist in equilibrium?
(CrO4)2- +2H+ (Cr2O7)2- +H2O
Shifted to the right in acidic solution and the left in alkaline solution
Why are complex ions coloured?
Movement between partly filled d-orbitals (movement between 3d and other shells too large
Ligands change the energy of an orbital as orbitals closer to the ligands have higher energy
‘Splits’ the orbitals into lower and higher energy orbitals
Split occurs so that total energy of 3d is the same
What does crystal field theory show?
More electrons allow a greater combination of transitions therefore transition metal ions undergo changes of colour when the oxidation number changes
How is the Cr2+ ion stable? What does it look like?
In red-coloured chromium (II) ethanoate
[Cr2(CH3CO2)4(H2O)2]
See picture
How is [Cr2(CH3CO2)4(H2O)2] made?
Reducing Cr3+ compound using zinc to form blue solution
Sodium ethanoate added to form bright red precipitate
When exposed to air, it will be oxidised to Cr3+ and turn grey-green
How is [Cr2(CH3CO2)4(H2O)2] made in the lab?
When tap funnel is opened, HCl runs into flask
Zn(s) +2HCl –> ZnCl2 + H2(g)
H2 reduces orange dichromate (VI) to green chromium (II) then to blue chromium (II)
(Cr2O7)2- + 6H+ + 4H2 –> 2Cr2+ + 7H2O
Once turned blue, tap is closed and pressure builds up, forcing content into boiling tube and producing red precipitate
2Cr2+ + 4CH3COO- +2H2O –> [Cr2(CH3CO2)4(H2O)2]
Adding OH- to hexaaqua 2+ ions
[M(H2O)6]2+ + 2OH- –> M(H2O)4(OH)2 + 2H2O
Acid base reaction
What is the exception for adding OH- to hexaaqua 2+ ions?
[Zn(H2O)6]2+ + 2OH- –> Zn(H2O)4(OH)2 + 2H2O
Zn(H2O)4(OH)2 + 2OH- –> [Zn(OH)4]2-
Adding OH- to hexaaqua 3+ ions
[Cr(H2O)6]3+ + 3OH- –> Cr(H2O)3(OH)3 + 3H2O
Cr(H2O)3(OH)3 + 3OH- –> [Cr(OH)6]3- + 3H2O
Smaller ion so more likely to polarise OH bond and break it, hence more likely to dissolve
What ions act as amphorteric hydroxides?
Zn2+ Al3+ Cr3+
ACID: Cr(H2O)3(OH)3 + OH- [Cr(H2O)2(OH)4]- + H2O
BASE: Cr(H2O)3(OH)3 + H+ [Cr(H2O)4(OH)2]- + H2O
What initial reaction occurs when small amounts of ammonia added to hexaaqua 2+ and 3+ ions?
[M(H2O)6]2+ + 2NH3 –> M(H2O)4(OH)2 + 2NH4+
[M(H2O)6]3+ + 3NH3 –> M(H2O)3(OH)3 + 3NH4+
Acid-base reaction
What reaction occurs when ammonia acts is added in excess to hexaaqua 2+ ions?
[Cu(H2O)6]2+ + 4NH3 –> Cu(NH3)4(H2O)2 + 4H2O
Ligand exhange reaction
Maximum of 4 ammonia ligands as it is slightly larger than H2O
Give 5 examples of transition metals acting as catalysts
TiCl3 in the polymerisation of ethene
Iron in the Haber process (or rubidium which is more effective but more expensive)
Vanadium in the Contact process
Platinum gauze in the first stage of the Ostwald process
Nickel in the hydrogenation of vegetable oils to make margarine
What is the Contact process?
Producing sulphur trioxide needed in the manufacture of sulphuric acid
2SO2(g) + O2(g) 2SO3(g)
How has the catalyst used in the Monsanto process developed?
Originally, cobalt and iodide co-catalyst used at 300C and 700 atm
Rhodium/iodide used which presented some problems so iridium presented as alternative
When used with ruthenium it is very active and reduces costs, CO2, drying columns and formation of by-products
What are the two types of catalysts?
Homogeneous- same phase as reactants
Heterogeneous- different phase from reactants
How does a heterogeneous reactant work?
Reactant molecules adsorbed onto surface of catalyst at active sites, weakening bonds between atoms
Reduces energy needed to break reactant molecules apart and increases chance of successful collision
If other molecules bind irreversibly, the catalyst is poisoned and will no longer work
Why are transition metals effective catalysts?
Exist in multiple oxidation states to provide alternative route
Why are catalysts finely divided?
Larger surface area allows more reactants to be adsorbed
What are the modern uses of transition metals?
Supra molecules
Chemotherapy
Photochromic lenses
How do photochromic lenses work?
Contain copper and silver halides which exist in equilibrium:
Cu+(s) + Ag+(s) Cu2+(s) + Ag(s)
In bright light, the equilibrium shifts and silver atoms are produced
How does chemotherapy work?
Uses chemicals to damage or destroy cancer cells, causing as little harm as possible to healthy tissue
Many drugs damage DNA or proteins involved in cell division
Cis-platin slows growth of cancer cells by binding to the DNA of nucleus and interfering with natural repair mechanisms
What alternatives are being developed to cis-platen?
Trans isomer which is used with other drugs to enhance effects without considerable damage
Gold which is small enough to pass through the membranes, delivering the drug to its target
Heat allows chemo dosage to be reduced whilst retaining same efficiency
