topic 15: transition metals Flashcards
what is the electronic configuration of Sc
1s2 2s2 2p6 3s2 3p6 4s2 3d1
what is the electronic configuration of Ti
1s2 2s2 2p6 3s2 3p6 4s2 3d2
what is the electronic configuration of V
1s2 2s2 2p6 3s2 3p6 4s2 3d3
what is the electronic configuration of Cr
1s2 2s2 2p6 3s2 3p6 4s1 3d5
what is the electronic configuration of Mn
1s2 2s2 2p6 3s2 3p6 4s2 3d5
what is the electronic configuration of Fe
1s2 2s2 2p6 3s2 3p6 4s2 3d6
what is the electronic configuration of Co
1s2 2s2 2p6 3s2 3p6 4s2 3d7
what is the electronic configuration of Ni
1s2 2s2 2p6 3s2 3p6 4s2 3d8
what is the electronic configuration of Cu
1s2 2s2 2p6 3s2 3p6 4s1 3d10
what is the electronic configuration of Zn
1s2 2s2 2p6 3s2 3p6 4s2 3d10
what is a transition metal
d-block elements that form one or more stable ions with incompletely-filled d-orbital
what are the characteristics of transition metals
- complex formation * formation of coloured ions
- variable oxidation state
- catalytic activity
why is Zn not a transition metal
Zn can only form a +2 ion. in this ion the Zn2+ has a complete d orbital and so does
not meet the criteria of having an incomplete d orbital in one of its compounds
why is Sc not a transition metal
Sc can only form a +3 ion. In this ion the Sc3+ has an empty d orbital and so does not meet the criteria of having an incomplete d orbital in one of its ions
what is a complex
s a central metal ion surrounded by ligands
what is a ligand
an atom, ion or molecule which can donate a lone electron pair
coordinate bonding
co-ordinate bonding is involved in complex formation. co-ordinate bonding is when the shared pair of electrons in the covalent bond
come from only one of the bonding atoms. co-ordination number: the number of co-ordinate bonds formed to a central
metal ion
ligands can be monodentate, bidentate or multidentate. what do these words mean
can form one coordinate bond per ligand
which have two atoms with lone pairs
and can form two coordinate bonds per ligand
describe the structure of EDTA4- anion
6 donor sites (4O and 2N) and forms a 1:1
complex with metal(II) ions
colour changes arise from changes in what 3 things
oxidation state
co-ordination number
ligand
[Co(NH3)6]2+ (aq) [Co(NH3)6]3+ (aq) +e- yellow —> brown
what causes the colour change in the equation
in this equation only oxidation state is changing
Cu(H2O)62+ + 4Cl- [CuCl4]2- + 6H2O
blue —> green
what causes the colour change in this equation
In this equation both ligand and co- ordination number are changing
Co(H2O)62+ + 6 NH3 Co(NH3)62+ + 6H2O
pink —> yellow brown
in this equation only the ligand is changing
how do colour arises
colour arises from electronic transitions from the ground state to excited states: between different d orbitals
a portion of visible light is absorbed to promote d electrons to higher energy levels. the light that is not absorbed is transmitted to give the substance colour
what colour does the solution appear if it absorbs orange light
blue
what will happen in changing a ligand or changing the coordination number
it will alter the energy split between the d- orbitals, changing deltaE and hence change the frequency of light absorbed
why does scandium have no colour
is a member of the d block, its ion (Sc3+) hasn’t got any d electrons left to move
around. so there is not an energy transfer equal to that of visible light
why do Zn2+ and Cu+ not have colour
in the case of Zn2+ ions and Cu+
ions the d shell is full e.g.3d10 so here there is no space for electrons to transfer. so there is not an energy transfer equal to that of visible light
what happens if visible light of increasing frequency is passed through a
sample of a coloured complex ion
some of the light is
absorbed
in a spectrophotometry what is the amount of light proportional to
proportional to the concentration of the absorbing species
some complexes have only pale colours and do not absorb light strongly. what is added to intensify the colour
a suitable ligand
what is used in spectrometry
absorption of visible light
what does spectrophotometry determine
the concentration of coloured ions
what is the method of using spectrophotometry
- add an appropriate ligand to intensify colour
- make up solutions of known concentration
- measure absorption or transmission
- plot graph of results or calibration curve
- measure absorption of unknown and compare
what is the common shape of the transition metal ions with small ligands. give example of ligand(s)
octahedral
e.g. H2O, OH- and NH3
what is the common shape of the transition metal ions with larger ligands. give example of ligand(s)
tetrahedral
what other complex shape is formed. give example(s)
square planar
what shape do complexes with the ligand Ag+ commonly form. give example
linear
e.g. [Ag(NH3)2]+, [Ag(S2O3)2]3- and
[Ag(CN)2]-
what is cisplatin used as and how does it work
an anticancer drug
platin binds to DNA of cancer cells and stops cancer cells diving
why does only the cisplatin version work
two chloride ions are displaced and
the molecule joins on to the DNA. in doing this it stops the replication of
cancerous cells
as well as stopping the replication of cancer cells, what else does cisplatin do
prevent the replication of healthy cells by bonding on to healthy DNA which may lead to unwanted side effects like hair loss
what is an example of a bidentate ligand
NH2CH2CH2NH2
what is an example of an multidentate ligands
EDTA4-
what is haemoglobin
an iron (II) complex containing a multidentate ligand
what does the Fe(II) in haemoglobin enable
oxygen to be transported in the blood
when does a ligand exchange reaction occur
when an oxygen molecule bound to
haemoglobin is replaced by a carbon monoxide molecule
why do H2O, OH- and NH3 act as monodentate ligands
they have an active lone pair of electrons on the outer energy level. these are used to form co-ordinate(dative) bonds with the metal ion
what CO to humans
toxic
why is CO toxic to humans
CO can from a strong coordinate bond with haemoglobin and replaces oxygen in a
ligand exchange reaction. this is a stronger bond than that made with oxygen and so it prevents the oxygen attaching to the haemoglobin
what are the 4 main oxidation states of vanadium
+5, +4, +3, +2
what colour does VO2+ with the oxidation number of +5 have
yellow solution
what colour does VO+2 with the oxidation number of +4 have
blue solution
what colour does V+3 with the oxidation number of +3 have
green solution
what colour does V2+ with the oxidation number of +2 have
violet solution
what does the ion with the V at the oxidation state +5 exist as
a solid
compound in the form of a VO3- ion, usually as NH4VO3
what would adding zinc to vanadium (V) in acidic solutions do
reduce the vanadium down through each successive oxidation state, and the colour would successively change from yellow to blue to green to violet
when transition metals form ions, what subshell do they lose their electrons from first
4s then 3d
what are the general trends in variable oxidation states
- relative stability of +2 state with respect to +3 state increases across the period
- compounds with high oxidation states tend to be oxidising agents e.g MnO4-
- compounds with low oxidation states are often reducing agents e.g V2+ & Fe2+
why do transition metals have various oxidation states
they are able to donate and receive electrons and are able to oxidize and reduce. This is because the ions contain partially filled sub-shells of d electrons that can easily lose or gain electrons. the energy differences between the oxidation states are small
what happens to the more negative Ecell
it moves to the right and gets oxidised
what happens when zinc reacts with vanadium. refer to Ecell
as zinc has a more negative electrode potential than all the vanadium half equations, zinc will reduce from to V2+
what happens when tin reacts with vanadium. refer to Ecell
vanadium will only be reduced with oxidation state 3+, 4+, 5+
what happens during the reduction chronium
Cr3+ (green) and then Cr2+ (blue) are formed by reduction of
Cr2O7 2- (orange) by the strong reducing agent zinc in (HCl) acid solution
is zinc or Fe2+ a stronger reducing agent
zinc
how will Fe2+ reduce chronium
will only reduce the dichromate to Cr3+
why would the zinc/dichromate be kept under a hydrogen atmosphere
to reduce it to Cr2+, because O2 in air will oxidise Cr2+ up to Cr3+
how can the Cr2+ state be stabilised
by forming a stable complex ion with a ligand such as the ethanoate ion
how would you know that chromium(II)
ethanoate is formed
if the blue Cr2+ ions are bubbled through sodium ethanoate, a stable red precipitate is formed
what can the reaction between Fe2+ and Cr2O72- in acid solution be used as
a quantitative redox titration
what is the equation of the reaction between Fe2+ and Cr2O7 2- in acid solution (include colour change)
Cr2O72- + 14H+ + 6Fe2+ 2Cr3+ + 7H2O + 6 Fe3+
orange ——> green
when is it easier to oxidise in alkaline conditions than acid conditions
when they have low oxidation states as it is easier to remove an electron from a negatively charged ion
what is the overall equation when Cr(OH)6
3- (aq)is oxidised into CrO42- (aq) by hydrogen peroxide
2 [Cr(OH)6]3- + 3H2O2 2CrO42- +2OH- + 8H2O
what are the steps in order to balance a half equation in alkaline conditions
Add H2O to balance O
Add H+ to balance H
Add OH- to both sides to cancel out H+
what happens during the chromate/ dichromate equilibrium
The chromate CrO42- and dichromate Cr2O72- ions can be converted from one to the other by the following equilibrium reaction
what is the equation of chromate/ dichromate equilibrium
2 CrO42- + 2H+ <–> Cr2O72- + H2O
what would happen if acid is added to the chromate/dichromate equilibrium
push the equilibrium to the dichromate (RHS)
what would happen if alkali is added to the chromate/dichromate equilibrium
push the equilibrium to the chromate (LHS)
in the formation of complex ions, is the ligand Lewis base or acid
lewis base bc it is donating a pair of electrons in the dative covalent bond and the metal ion is the Lewis acid
what is a Lewis base
electron pair donator
what is a Lewis acid
electron pair acceptor
in solution Cr(III) often appears green and
Fe(III) appears yellow/brown, why?
when can the ruby and violet colour be seen
due to hydrolysis reactions.
the ruby and violet colour is only really seen in solid hydrated salts that contain these complexes
what is the equation of the hydrolysis of a 2+ metal complex and 3+ metal complex
[M(H2O)6]2+ + H2O [M(H2O)5(OH)]+ +H3O+
[M(H2O)6]3+ + H2O [M(H2O)5(OH)]2+ H3O+
why is the acidity of [M(H2O)6]3+ is greater than that of [M(H2O)6]2+
because the 3+ metal ions have higher charge density (charge/size ratio) and have greater polarising power. the greater the polarising power, the more strongly it attracts the water molecule. this weakens the O-H bond so it breaks more easily releasing H+ ions
[Cu(H2O)6 ]2+ (aq) + EDTA4- (aq) [Cu (EDTA)]2- (aq) + 6H2O (l)
explain the entropy change of this reaction
- the copper complex ion has changed from having monodentate ligands to a multidentate ligand
- in this reaction there is an increase in the entropy of the system because there are more moles of products than reactants (from 2 to 7)
- this creates more disorder
the stability of the EDTA complexes has many applications. what are the uses of EDTA
- added to rivers to remove poisonous heavy metal ions
—–> the EDTA complexes are not toxic - it is in many shampoos to remove
calcium ions present in hard water
—–>so helping lathering
what type of ligand is ethane-1-2-diamine
bidentate ligand
the Stotal is positive for this equation
[Co(NH3)6]2+ + 3NH2CH2CH2NH2 —>[Co(NH2CH2CH2NH2)3]2+ + 6NH3
explain why
- this reaction has an increase in entropy because of in the increase in moles from 4 to 7 in the reaction so ΔSsystem is positive
- its enthalpy change ΔH (and ΔSsurroundings) is close to zero as the
number of dative covalent and type (N to metal coordinate bond) are the same so the energy required to break and make bonds will be the same
how does ethane-1-2-diamine act as a base
can carry out the deprotonation reactions
(similar to those of ammonia) forming hydroxide precipitates
when would the partial substitution of ethanedioate ions occur and what is formed
- when a dilute aqueous solution containing
ethanedioate ions is added to a solution
containing aqueous copper(II) ions - in this reaction four water molecules are replaced and a new complex is formed
what are ligand exchange equations with ethanedioate ions
Cu(H2O)6 2+ + 3C2O42- —-> [Cu(C2O4)3]4- + 6H2O
Cr(H2O)6 3+ + 3C2O42- [Cr(C2O4)3]3- + 6H2O
in a complex ion containing a Cl- as a ligand, how are the Cl- arranged
have Cl ions acting as ligands inside the complex and Cl ions outside the complex attracted ionically to it
what would happen if silver nitrate is added to the complex containing Cl- ions
it will only form the silver chloride precipitate with the free chloride ions outside of the complex
what are catalysts
increase reaction rates without getting used up. they do this by providing an alternative route with a lower activation energy
what is a heterogeneous catalyst
in a different phase from the reactants
what is a homogeneous catalyst
in the same phase as the reactants
where does heterogeneous catalysis occur
on the surface of the catalyst
what happens during heterogeneous catalysis
- adsorption of reactants at active sites on the surface may lead to catalytic action
- the active site is the place where
the reactants adsorb on to the surface of the catalyst. This can result in the bonds within the reactant molecules becoming weaker, or the molecules being held in a more reactive configuration
there will also be a higher concentration of reactants at the solid surface so leading to
a higher collision frequency
the strength of adsorption determines the
effectiveness of the catalytic activity
- some metals e.g. W have too strong adsorption and so the products cannot be released
- some metals e.g. Ag have too weak adsorption, and the reactants do not adsorb in high enough concentration
referring to the strength of adsorption, why are Pt and Ni catalysts used
they have about the right strength and are most useful as catalysts
what would happen when the surface area of a solid catalyst increases
will improve its effectiveness. a support medium is often used to maximise the surface area and minimise the cost
what are advantages of heterogeneous catalysts
- they can be filtered off and are easy
to separate from any liquid or gaseous products - they are suited to continuous processes rather than batch processes
what is an example of a heterogeneous catalyst
V2O5
is used as a catalyst in the Contact Process.
overall equation : 2SO2 + O2 —> 2SO3
step 1 SO2 + V2O5 —> SO3 + V2O4
step 2 2V2O4 + O2 —> 2V2O5
what are the steps in heterogeneous catalysis in catalytic converter
- CO and NO molecules form bonds with atoms at active sites on the surface of the catalyst - adsorbed onto the surface
- as a result bonds in the reactants are weakened and break
- new bonds form between the reactants held close together on catalyst surface
- desorption of CO2 and N2 product molecules from the surface of the catalyst
what do catalytic converters do
these remove CO, NOx and unburned hydrocarbons (e.g. octane, C8H18) from the exhaust gases, turning them into ‘harmless’ CO2, N2 and H2O.
how do catalytic converters have a large surface area
they have a ceramic honeycomb coated
with a thin layer of catalyst metals Platinum, Palladium, Rhodium
making ethanoic acid from methanol and carbon monoxide is a preferable industrial production method, why?
because it has a high atom economy
when catalyst and reactants are in the same phase, what does the reaction undergo
the reaction proceeds through an
intermediate species
why are transition metals able to act as homogeneous catalysts
- because they can form various oxidation states
- they are able to donate and receive electrons and are able to oxidize and reduce
- this is because the ions contain partially filled sub-shells of d electrons that can easily lose or gain electrons
in the reaction between iodide and persulfate ions, why is the uncatalysed reaction very slow
because the reaction needs a collision between two negative ions. repulsion
between the ions is going to hinder this – meaning high activation energy
in the catalysed reaction between I- and S2O8 2-, why does it have a lower activation energy
both of the individual stages in the catalysed mechanism involve collision between positive and negative ions
what is the reaction between I- and S2O8 2- ‘ s catalyst
Fe2+
(Fe3+ ions can also act as the catalyst because the two steps in the catalysed mechanism can occur in any order)
how can you construct a catalysed mechanism of the reaction
- split full equation into its two
half equations - add in cobalt to make two
new redox equations. - making sure the oxidised
cobalt equation is combined
with the original reduced half
equation and vice versa
