transition elements&catalysts
DESCRIPTION
Transition Elements&Catalysts http://www.chem.ox.ac.uk/vrchemistry/complex/allbottlesmsiedefault.html http://www.gcsescience.com/pt21.htm. TRANSITION METALS. High densities , melting and boiling points Ability to exist in a variety of oxidation states Formation of colored ions - PowerPoint PPT PresentationTRANSCRIPT
Transition Elements&Catalysts
http://www.chem.ox.ac.uk/vrchemistry/complex/allbottlesmsiedefault.html
http://www.gcsescience.com/pt21.htm
TRANSITION METALS
• High densities,melting and boiling points• Ability to exist in a variety of oxidation
states• Formation of colored ions• Ability to form complex ions• Ability to act as catalysts
Zn and Sc do not share these properties.
THE FIRST ROW TRANSITION ELEMENTS
Definition D-block elements forming one or more stable ions withpartially filled (incomplete) d-sub shells.
The first row runs from scandium to zinc filling the 3d orbitals.
Properties arise from an incomplete d sub-shell in atoms or ions
THE FIRST ROW TRANSITION ELEMENTS
Metallicproperties all the transition elements are metals
strong metallic bonds due to small ionic size and close packing higher melting, boiling points and densities than s-block metals
K Ca Sc Ti V Cr Mn Fe Co
m. pt / °C 63 850 1400 1677 1917 1903 1244 1539 1495
density /g cm-3 0.86 1.55 3 4.5 6.1 7.2 7.4 7.9 8.9
4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
POTASSIUM
1s2 2s2 2p6 3s2 3p6 4s1
In numerical terms one would expect the 3d orbitals to be filled next.However, because the principal energy levels get closer together as you go further from the nucleus coupled with the splitting into sub energy levels, the 4s orbital is of a LOWER ENERGY than the 3d orbitals so gets filled first.
‘Aufbau’ Principle
INC
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SIN
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/ D
ISTA
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N
UC
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S
4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
CALCIUM
1s2 2s2 2p6 3s2 3p6 4s2
As expected, the next electron in pairs up to complete a filled 4s orbital.This explanation, using sub levels fits in with the position of potassium and calcium in the Periodic Table. All elements with an -s1 electronic configuration are in Group I and all with an -s2 configuration are in Group II.
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N
UC
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4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
SCANDIUM
1s2 2s2 2p6 3s2 3p6 4s2 3d1
With the lower energy 4s orbital filled, the next electrons can now fill p the 3d orbitals. There are five d orbitals. They are filled according to Hund’s Rule.BUT WATCH OUT FOR TWO SPECIAL CASES.
INC
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N
UC
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4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
TITANIUM
1s2 2s2 2p6 3s2 3p6 4s2 3d2
The 3d orbitals are filled according to Hund’s rule so the next electron doesn’t pair up but goes into an empty orbital in the same sub level.
HUND’S RULE OFMAXIMUM MULTIPLICITY
INC
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N
UC
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4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
VANADIUM
1s2 2s2 2p6 3s2 3p6 4s2 3d3
The 3d orbitals are filled according to Hund’s rule so the next electron doesn’t pair up but goes into an empty orbital in the same sub level.
HUND’S RULE OFMAXIMUM MULTIPLICITY
INC
REA
SIN
G E
NER
GY
/ D
ISTA
NC
E FR
OM
N
UC
LEU
S
4s
3 3p
3d
44p
4d
4fIN
CR
EASI
NG
EN
ERG
Y /
DIS
TAN
CE
FRO
M
NU
CLE
US
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
CHROMIUM
1s2 2s2 2p6 3s2 3p6 4s1 3d5
One would expect the configuration of chromium atoms to end in 4s2 3d4.To achieve a more stable arrangement of lower energy, one of the 4s electrons is promoted into the 3d to give six unpaired electrons with lower repulsion.
4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
MANGANESE
1s2 2s2 2p6 3s2 3p6 4s2 3d5
The new electron goes into the 4s to restore its filled state.
INC
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N
UC
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4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
IRON
1s2 2s2 2p6 3s2 3p6 4s2 3d6
Orbitals are filled according to Hund’s Rule. They continue to pair up.
HUND’S RULE OFMAXIMUM MULTIPLICITY
INC
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ISTA
NC
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N
UC
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4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
COBALT
1s2 2s2 2p6 3s2 3p6 4s2 3d7
Orbitals are filled according to Hund’s Rule. They continue to pair up.
HUND’S RULE OFMAXIMUM MULTIPLICITY
INC
REA
SIN
G E
NER
GY
/ D
ISTA
NC
E FR
OM
N
UC
LEU
S
4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
NICKEL
1s2 2s2 2p6 3s2 3p6 4s2 3d8
Orbitals are filled according to Hund’s Rule. They continue to pair up.
HUND’S RULE OFMAXIMUM MULTIPLICITY
INC
REA
SIN
G E
NER
GY
/ D
ISTA
NC
E FR
OM
N
UC
LEU
S
4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
COPPER
1s2 2s2 2p6 3s2 3p6 4s1 3d10
One would expect the configuration of copper atoms to end in 4s2 3d9.To achieve a more stable arrangement of lower energy, one of the 4s electrons is promoted into the 3d.
HUND’S RULE OFMAXIMUM MULTIPLICITY
INC
REA
SIN
G E
NER
GY
/ D
ISTA
NC
E FR
OM
N
UC
LEU
S
4s
3 3p
3d
44p
4d
4f
ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
ZINC
1s2 2s2 2p6 3s2 3p6 4s2 3d10
The electron goes into the 4s to restore its filled state and complete the 3d and 4s orbital filling.
INC
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K 1s2 2s2 2p6 3s2 3p6 4s1
Ca 1s2 2s2 2p6 3s2 3p6 4s2 Sc 1s2 2s2 2p6 3s2 3p6 4s2 3d1
Ti 1s2 2s2 2p6 3s2 3p6 4s2 3d2
V 1s2 2s2 2p6 3s2 3p6 4s2 3d3
Cr 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Mn 1s2 2s2 2p6 3s2 3p6 4s2 3d5
Fe 1s2 2s2 2p6 3s2 3p6 4s2 3d6
Co 1s2 2s2 2p6 3s2 3p6 4s2 3d7
Ni 1s2 2s2 2p6 3s2 3p6 4s2 3d8
Cu 1s2 2s2 2p6 3s2 3p6 4s1 3d10
Zn 1s2 2s2 2p6 3s2 3p6 4s2 3d10
ELECTRONIC CONFIGURATIONS
VARIABLE OXIDATION STATES
Arises from the similar energies required for removal of 4s and 3d electrons
When electrons are removed they come from the 4s orbitals first
Cu 1s2 2s2 2p6 3s2 3p6 3d10 4s1 Ti 1s2 2s2 2p6 3s2 3p6 3d2 4s2
Cu+ 1s2 2s2 2p6 3s2 3p6 3d10 Ti2+ 1s2 2s2 2p6 3s2 3p6 3d2
Cu2+ 1s2 2s2 2p6 3s2 3p6 3d9 Ti3+ 1s2 2s 2p6 3s2 3p6 3d1
Ti4+ 1s2 2s2 2p6 3s2 3p6
maximum rises across row to manganese
maximum falls as the energy required toremove more electrons becomes very high
all (except scandium) have an M2+ ion
stability of +2 state increases across the rowdue to increase in the 3rd Ionisation Energy
THE MOST IMPORTANT STATES ARE IN RED
Ti Sc V Cr Mn Fe Co Ni Cu Zn
+1
+2
+3
+4
+5
+6
+2 +2 +2 +2 +2 +2 +2 +2
+6
+7
+3+3 +3
+4
+3
+4
+3 +3 +3
+4 +4 +4 +4
+5 +5 +5 +5
+6
COLOURED IONS
Theory ions with a d10 (full) or d0 (empty) configuration are colourless ions with partially filled d-orbitals tend to be coloured it is caused by the ease of transition of electrons between energy levels energy is absorbed when an electron is promoted to a higher level the frequency of light is proportional to the energy difference
ions with d10 (full) Cu+,Ag+ Zn2+
or d0 (empty) Sc3+ configuration are colourlesse.g. titanium(IV) oxide TiO2 is white
colour depends on ... transition elementoxidation stateligandcoordination number
A characteristic of transition metals is their ability to form coloured compounds
3d ORBITALSThere are 5 different orbitals of the d variety
z2x2-y2
xy xz yz
COLOURED IONS
Absorbed colour nm Observed colour nmVIOLET 400 GREEN-YELLOW 560BLUE 450 YELLOW 600BLUE-GREEN 490 RED 620YELLOW-GREEN 570 VIOLET 410YELLOW 580 DARK BLUE 430ORANGE 600 BLUE 450RED 650 GREEN 520
The observed colour of a solution depends on the wavelengths absorbed
Copper sulphate solution appears blue because the energy absorbed corresponds to red and yellow wavelengths. Wavelengths corresponding to blue light aren’t absorbed.
WHITE LIGHT GOES IN
SOLUTION APPEARS BLUE
ENERGY CORRESPONDING TO THESE COLOURS IS ABSORBED
COLOURED IONS
a solution of copper(II)sulphate is blue becausered and yellow wavelengths are absorbed
white lightblue and green not absorbed
Coordination Compound
• Go to Power Point Coordination Chemistry
COMPLEX IONS - LIGANDS
Formation ligands form co-ordinate bonds to a central transition metal ion
Ligands atoms, or ions, which possess lone pairs of electronsform co-ordinate bonds to the central iondonate a lone pair into vacant orbitals on the central species
Ligand Formula Name of ligandchloride Cl¯ chlorocyanide NC¯ cyanohydroxide HO¯ hydroxooxide O2- oxowater H2O aquaammonia NH3 ammine
some ligands attach themselves using two or more lone pairsclassified by the number of lone pairs they usemultidentate and bidentate ligands lead to more stable complexes
COMPLEX IONS - LIGANDS
some ligands attach themselves using two or more lone pairsclassified by the number of lone pairs they usemultidentate and bidentate ligands lead to more stable complexes
Unidentate form one co-ordinate bond Cl¯, OH¯, CN¯, NH3, and H2O
Bidentate form two co-ordinate bonds H2NCH2CH2NH2 , C2O42-
COMPLEX IONS - LIGANDS
some ligands attach themselves using two or more lone pairsclassified by the number of lone pairs they usemultidentate and bidentate ligands lead to more stable complexes
Multidentate form several co-ordinate bonds
EDTA
An important complexing agent
d orbitals
http://www.chemguide.co.uk/inorganic/complexions/colour.html
• When the ligands bond with the transition metal ion, there is repulsion between the electrons in the ligands and the electrons in the d orbitals of the metal ion. That raises the energy of the d orbitals.
• However, because of the way the d orbitals are arranged in space, it doesn't raise all their energies by the same amount. Instead, it splits them into two groups
http://www.chemguide.co.uk/inorganic/complexions/colour.html
• The diagram shows the arrangement of the d electrons in a Cu2+ ion before and after six water molecules bond with it.
• Whenever 6 ligands are arranged around a transition metal ion, the d orbitals are always split into 2 groups in this way - 2 with a higher energy than the other 3.
• The size of the energy gap between them (shown by the blue arrows on the diagram) varies with the nature of the transition metal ion, its oxidation state (whether it is 3+ or 2+, for example), and the nature of the ligands.
• When white light is passed through a solution of this ion, some of the energy in the light is used to promote an electron from the lower set of orbitals into a space in the upper set.
• http://www.chemguide.co.uk/inorganic/complexions/colour.html
SPLITTING OF 3d ORBITALS
Placing ligands around a central ion causes the energies of the d orbitals to change Some of the d orbitals gain energy and some lose energy In an octahedral complex, two go higher and three go lower In a tetrahedral complex, three go higher and two go lower
Degree of splitting depends on the CENTRAL ION and the LIGAND
The energy difference between the levels affects how much energy is absorbed when an electron is promoted. The amount of energy governs the colour of light absorbed.
3d 3d
OCTAHEDRAL TETRAHEDRAL
Complex ion - Iron• Because of their size, transition metals attract
species that are rich in electrons. Ligands.
• Water is a common ligand as in hexaaquairon (III) ion, [Fe(H2O)6 3+
COMPLEX IONS - LIGANDS
some ligands attach themselves using two or more lone pairsclassified by the number of lone pairs they usemultidentate and bidentate ligands lead to more stable complexes
Multidentate form several co-ordinate bonds
HAEM
A complex containing iron(II) which is responsible for the red colour in blood and for the transport of oxygen by red blood cells.
Co-ordination of CO molecules interferes with the process
COMPLEX IONS - LIGANDS
some ligands attach themselves using two or more lone pairsclassified by the number of lone pairs they usemultidentate and bidentate ligands lead to more stable complexes
Multidentate form several co-ordinate bonds
CO-ORDINATION NUMBER & SHAPE the shape of a complex is governed by the number of ligands around the central ion the co-ordination number gives the number of ligands around the central ion a change of ligand can affect the co-ordination number
Co-ordination No. Shape Example(s)
6 Octahedral [Cu(H2O)6]2+
4 Tetrahedral [CuCl4]2-
Square planar Pt(NH3)2Cl2
2 Linear [Ag(NH3)2]+
ISOMERISATION IN COMPLEXES
GEOMETRICAL (CIS-TRANS) ISOMERISM
Square planar complexes of the form [MA2B2]n+ exist in two forms
trans platin cis platin
An important anti-cancer drug. It is a square planar, 4 co-ordinate complex of platinum.
13.2.7 Catalytic Action of Transition Elements
• Catalysts increase the rate of a chemical reaction without themselves being chemically changed(lower EA).
• They can be heterogeneous( catalyst is in a different phase from the reactants) or homogeneous( same phase)
• Transition metals are good at adsorbing small molecules.
• Read CC page 59,60. Outline due Monday.
13.2.7. CATALYTIC PROPERTIES
Transition metals and their compounds show great catalytic activity
It is due to partly filled d-orbitals which can be used to form bonds with adsorbed reactants which helps reactions take place more easilyTransition metals can both lend electrons to and take electrons from other molecules. By giving and taking electrons so easily, transition metal catalysts speed up reactions
Examples of catalysts
IRON Manufacture of ammonia - Haber Process
NICKEL Hydrogenation reactions - margarine manufacture
MANGANESE IV OXIDE Hydrogen peroxide
VANADIUM(V) OXIDE Manufacture of sulphuric acid - Contact Process
http://www.gcsescience.com/pt21.htm
Co in Vitamin B12Vitamin B12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins. It is normally involved in the metabolism of every cell of the human body, especially affecting DNA synthesis and regulation, but also fatty acid synthesis and energy production.
Contact Process• Vanadium pentoxide is used in different, industrial processes as
catalyst: In the contact process it serves for the oxidation of SO2 to SO3 with oxygen at 440°C.
• Sulfur dioxide and oxygen then react as follows:
• 2 SO2(g) + O2(g) 2 SO⇌ 3(g) : ΔH = −197 kJ mol−1
• To increase the reaction rate, high temperatures (450 °C), medium pressures (1-2 atm), and vanadium(V) oxide (V2O5) are used to ensure a 96% conversion. Platinum would be a more effective catalyst, but it is very costly and easily poisoned.[citation needed]
• The catalyst only serves to increase the rate of reaction as it has no effect on how much SO3 is produced. The mechanism for the action of the catalyst is:
• 2SO2 + 4V5+ + 2O2- → 2SO3 + 4V4+ 4V4+ + O2 → 4V5+ + 2O2-
• http://www.chemguide.co.uk/physical/equilibria/contact.html
13.2.8. Economic Significance of catalysts in Contact and Haber processes
• The catalytic properties of these metals are due to their ability to exist in a number of stable oxidation states and the presence of empty orbitals for temporary bond formation.
• The catalyst is usually a powdered solid and the reactants a mixture of gases.
Decomposition of Hydrogen Peroxide – MnO2
Hydrogen peroxide decomposes to oxygen and water when a small amounts of manganese dioxide is added. Catalase enzyme from potato also decomposes hydrogen peroxide.
2 H2O2 → 2 H2O + O2
Catalytic Converter
http://auto.howstuffworks.com/catalytic-converter2.htm
Catalytic Converters
13.6
CO + Unburned Hydrocarbons + O2 CO2 + H2Ocatalyticconverter
2NO + 2NO2 2N2 + 3O2
catalyticconverter
Ostwald Process
Hot Pt wire over NH3 solutionPt-Rh catalysts used
in Ostwald process
4NH3 (g) + 5O2 (g) 4NO (g) + 6H2O (g)Pt catalyst
2NO (g) + O2 (g) 2NO2 (g)
2NO2 (g) + H2O (l) HNO2 (aq) + HNO3 (aq)
13.6
http://hferrier.co.uk/higher/unit1a/unit1a.htm
• They increase the rates of reaction and decrease the time needed for a reaction to reach equilibrium. They increase the efficiency of industrial processes and help reduce costs and so increase profits.
• So, a catalyst affects the transition state and activation path. How does it do this? Typically, by complexing one of the reagents. Complexation by transition metals affords access to a wide variety of oxidation states for the metal. This has the property of providing electrons or withdrawing electrons from the transition state of the reaction. That is, if the transition state is electron rich, then the transition metal might hold some of that electron density and those prevent too much from building up on the reagent. This would then facilitate the reaction. Or the transition metal might undergo formal oxidation/reduction to achieve electron transfer to a substrate, thereby allowing a reaction to occur. This is "complexation and electron storage" taken to the extreme but is a common mechanism in organometallic chemistry. Indeed, a variety of catalytic pathways rely on a two electron transfer between the metal and the substrate (e.g. hydroformylation). It is the ability of the transition metal to be in a variety of oxidation states, to undergo facile transitions between these oxidation states, to coordinate to a substrate, and to be a good source/sink for electrons that makes transition metals such good catalysts.