Transition Elements&Catalysts

Transition Elements&Catalysts

http://www.chem.ox.ac.uk/vrchemistry/complex/allbottlesmsiedefault.html

http://www.gcsescience.com/pt21.htm

http://www.chem.ox.ac.uk/vrchemistry/complex/allbottlesmsiedefault.html


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‘Aufbau’ Principle

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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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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.

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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


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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.



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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


MANGANESE

1s2 2s2 2p6 3s2 3p6 4s2 3d5

The new electron goes into the 4s to restore its filled state.

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IRON

1s2 2s2 2p6 3s2 3p6 4s2 3d6

Orbitals are filled according to Hund’s Rule. They continue to pair up.



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COBALT

1s2 2s2 2p6 3s2 3p6 4s2 3d7




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NICKEL

1s2 2s2 2p6 3s2 3p6 4s2 3d8




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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.



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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.

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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 ORBITALS

There 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 aqua

ammonia 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



Unidentate form one co-ordinate bond Cl¯, OH¯, CN¯, NH3, and H2O

Bidentate form two co-ordinate bonds H2NCH2CH2NH2 , C2O42-



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




• 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+




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




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.chemeddl.org/collections/tsts/stahl/Stahl9-12/Transitionorbitals9to12.html


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.

http://en.wikipedia.org/wiki/Vitamin

http://en.wikipedia.org/wiki/Brain

http://en.wikipedia.org/wiki/Nervous_system

http://en.wikipedia.org/wiki/Blood

http://en.wikipedia.org/wiki/B_vitamins

http://en.wikipedia.org/wiki/Metabolism

http://en.wikipedia.org/wiki/Cell_(biology)

http://en.wikipedia.org/wiki/DNA

http://en.wikipedia.org/wiki/Fatty_acid

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

http://en.wikipedia.org/wiki/Oxygen

http://en.wikipedia.org/wiki/Atmosphere_(unit)

http://en.wikipedia.org/wiki/Vanadium(V)_oxide

http://en.wikipedia.org/wiki/Platinum

http://en.wikipedia.org/wiki/Catalyst_poisoning

http://en.wikipedia.org/wiki/Wikipedia:Citation_needed

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.

http://hferrier.co.uk/higher/unit1a/unit1a.htm

• 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.

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Transition Elements&Catalysts