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Transition Metals
A transition metal is an element having an incomplete d sub shell either in its atomic or its common
ionic form
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Central block of periodic table, known as d-block
Zinc does not fit definition as atom and ions all have complete sub shells

Four Transition Element Characteristics, Due to the partially filled d sub- shells in their atoms or ions;
 Variable oxidation states
 Formation of complexes
 Formation of coloured ions
 Catalytic activity
Variable Oxidation States
 Transition metals have electrons of similar energies in the 3d and 4s energy levels
 A particular element may form ions of roughly equal stability by losing different numbers of
electrons
 All transition elements have variable oxidation states, some more forms than others
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Ti=+4, V=+5, Cr= +6, Mn=+7
 After Mn, the increasing nuclear charge binds the electrons more strongly so that the +2
oxidation state becomes more common
Variable Oxidation States of Vanadium
 Vanadium exists in several different oxidation states in a number of complexes
o Salt; Ammonium Vanadate(V) NH4VO3 has max
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VO3- + 2H+ VO2+ + H2O
o Powdered zinc metal is now added to the yellow solution which releases 2
electrons as it reacts with the acid to become Zn(II)
Zn  Zn2+ + 2eThese electrons released are able to reduce Vanadium (V) through its oxidation states +4, +3 and +2
accompanied by distinct colour changes
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V(V) V(IV) V(III) V(II)
VO2+
VO2+
V3+
V2+
Yellow Blue
Green Violet

Variable Oxidation States of Chromium
V(IV) V(III) V(II)
Cr2O72- Cr3+
Cr2+
Orange Green Blue
Cr(II) is very easily oxidised to Cr(III) and will not be seen unless no air is present
Variable Oxidation States of Manganese
Manganese has a highest oxidation state of +7 as MnO 4- which is a powerful oxidising agent and may
be reduced directly to lowest oxidation state of +2 by reaction with Zn or Fe(II) in acid solution
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All ligands are Lewis Bases as they are lone pair donors used to form a co-ordinate
bond with the metal ion
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-3 Ethanedioate (Oxalate) ions Cr(C2O4)33-

-Ni(NH2CH2CH2NH2)32+

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Each ligand takes up two of the positions at right angles to each other
Co-ordinate number is 6 as 6 bonds formed

Multidentate
A multidentate ligand has 4 or 6 lone pairs
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Has 4 Nitrogen atoms with 4 lone pairs at centre
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 4 Coordinate bonds formed with haem, but still has space for two more, one below and
above plane of ring
 Globin protein attaches to additional one of positions using N with lone pair on its amino
acids
 Water or oxygen can be added to other position- how O2 is carried around the body
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Lewis in 1923;
An acid substance is one which can employ a lone pair from another molecule in completing
the stable group of one of it’s own atom
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A Lewis Base
A Lewis base is any species that donates a pair of electrons to a Lewis Acid to form a Lewis addut
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Number is determined by size of water molecules and Cu2+ ions
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Aldehydes produce a positive ‘silver mirror’
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AgCl + 2NH3  [Ag(NH3)2]+ + Cl-

Catalysis
A catalyst alters the rate of a chemical reaction without being used up or undergoing any permanent
chemical change
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A Maxwell- Boltzman distribution curve shows us the amount of kinetic energy a particle
has
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When activation energy is lowered by the catalyst a higher proportion of molecules will have
sufficient energy to react
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Most industrial catalysts are transition metals
Heterogeneous Catalysts
 Catalyst in a different phase from the reactants- catalyst solid, reactant gases
 May be transition metals or transition metal complexes
 Heterogeneous catalysis occurs on the surface of the solid catalyst where the active sites are
located where at least one of the reactants is adsorbed by forming weak chemical bonds
with the metal atoms

Catalysis work in three stages;
Adsorption- Formation of bonds with the metal may use some of the electrons from bonds within
the gas molecules thus weakening these bonds and making a subsequent reaction easier
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This increases the chances of favourable collisions taking place
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This will
reduce the activation energy
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This
will reduce the activation energy
 Concentration of reactants on a surface will be increased, increase collision rates of
reactant molecules
Efficiency of a catalyst will depend on how strongly or weakly the reactant molecules are adsorbed
on the catalyst surface
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Silver is not a good catalyst as there are few d- orbitals available for bonding with the
reactant molecules so it adsorbs too weakly
If only a partial reaction is wanted, a weak catalyst allows the desorption before further oxidation
can occur
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Surface will become ‘poisoned’ by the reactant molecules
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Sulphur compounds have a tendency to poison transition metal catalyst
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Tungsten is too strong catalyst
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Nickel and platinum achieve this balance and are generally excellent catalyst
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Presence of iron(II) allows the
peroxdisulphate(VI) ions to oxidise the iron(II) to iron(III) and then the ioide ions reduce iron(III) to
iron(II)
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As soon as some of the colour has disappeared (Mn(VII) to Mn(II)), further
addition of Mn(VII) is decolourised instantly
Increasing the Efficiency of catalysts
 Increase surface area of heterogeneous catalyst as reactions can only take place on surface
 Expensive catalyst are spread thinly across an inert support medium- increases SA and
reduces cost
 Mixed catalyst
Catalytic converters in cars use two expensive catalyst- platinum and rhodium spread across cheap
inert support
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Transition metals have an incompletely filled d- subshell so that colour can arise from
electronic transitions from the ground state to excited states
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Difference is
E2 –E1= ΔE= hv
-34
h= Plancks constant (6
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Some of visible wavelength radiation will be absorbed, the exact frequency will depend on
the transition metal, its oxidation, the co-ordination number and type of ligand
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Transition metals have an important ability to form compounds in which the metals oxidation stte is
different
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e
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Any surplus oxygen will be
converted into water by reaction with hydrogen ions from acid present
Example 1- Dichromate (VII) ions reduced to chromium (III) by sulphite ions which are oxidised to
sulphate ions
Cr2O72- + 14H+ +6e- >>>> 2Cr3+ + 7H2O
SO32- + H2O >>>> SO42- + 2H+ +2eCr2O72- + 8H+ +3SO32- >>>>3SO42- + 4H2O + 2Cr3+
Example 2- Manganate(VII) ions MnO4- can be reduced to Manganese(II), Mn2+ by iron(II) ions, Fe2+
which are oxidised to iron(III) ions Fe3+
MnO4- + 8H+ + 5e- >>>> Mn2+ 4H2O
Fe2+ >>>> Fe3+ eMnO4- + 8H+ + 5Fe2+ >>>> Mn2+ + 4H2O + 5Fe3+



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