1. Transition Elements&Catalysts

2. 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.

3. THE FIRST ROW TRANSITION ELEMENTS
Definition D-block elements forming one or more stable ions with
partially 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

4. THE FIRST ROW TRANSITION ELEMENTS
Metallic
properties 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

5. Sc and Zn
A transition metal is one which forms one or more stable ions which have incompletely filled d orbitals.

6. Scandium
Scandium has the electronic structure [Ar] 3d14s2. When it forms ions, it always loses the 3 outer electrons and ends up with an argon structure.
The Sc3+ ion has no d electrons and so doesn't meet the definition.

7. Zinc
Zinc has the electronic structure [Ar] 3d104s2. When it forms ions, it always loses the two 4s electrons to give a 2+ ion with the electronic structure [Ar] 3d10.
The zinc ion has full d levels and doesn't meet the definition either.

8. Copper
By contrast, copper, [Ar] 3d104s1, forms two ions. In the Cu+ ion the electronic structure is [Ar] 3d10. However, the more common Cu2+ ion has the structure [Ar] 3d9.
Copper is definitely a transition metal because the Cu2+ ion has an incomplete d level.

9. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
POTASSIUM 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
1s2 2s2 2p6 3s2 3p6 4s1
‘Aufbau’ Principle
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.

10. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
CALCIUM 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
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.

11. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
SCANDIUM 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
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.

12. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
TITANIUM 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
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 OF
MAXIMUM MULTIPLICITY

13. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
VANADIUM 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
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 OF
MAXIMUM MULTIPLICITY

14. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
CHROMIUM 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
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.

15. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
MANGANESE 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
1s2 2s2 2p6 3s2 3p6 4s2 3d5
The new electron goes into the 4s to restore its filled state.

16. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
IRON 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
1s2 2s2 2p6 3s2 3p6 4s2 3d6
Orbitals are filled according to Hund’s Rule. They continue to pair up.
HUND’S RULE OF
MAXIMUM MULTIPLICITY

17. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
COBALT 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
1s2 2s2 2p6 3s2 3p6 4s2 3d7
Orbitals are filled according to Hund’s Rule. They continue to pair up.
HUND’S RULE OF
MAXIMUM MULTIPLICITY

18. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
NICKEL 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
1s2 2s2 2p6 3s2 3p6 4s2 3d8
Orbitals are filled according to Hund’s Rule. They continue to pair up.
HUND’S RULE OF
MAXIMUM MULTIPLICITY

19. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
COPPER 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
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 OF
MAXIMUM MULTIPLICITY

20. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS
ZINC 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
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.

21. ELECTRONIC CONFIGURATIONS
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

22. To write the electronic structure for Fe3+:
Fe 1s22s22p63s23p63d64s2 Fe3+1s22s22p63s23p63d5
The 4s electrons are lost first followed by one of the 3d electrons.
The rule is quite simple. Take the 4s electrons off first, and then as many 3d electrons as necessary to produce the correct positive charge.

23. When d-block elements form ions, the 4s electrons are lost first.
For Cr
[Ar]4s13d5 is the configuration for chromium atom. It has this rather than two electrons in the 4s as it is more stable like this. When it forms 3+ it has the configuration [Ar]4s03d3 as the 4s will be lost first as they are at a lower energy level.

25. VARIABLE OXIDATION STATES
Arises from the similar energies required for removal of 4s and 3d electrons
maximum rises across row to manganese
maximum falls as the energy required to
remove more electrons becomes very high
all (except scandium) have an M2+ ion
stability of +2 state increases across the row
due 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 +7
When electrons are removed they come from the 4s orbitals first
Cu 1s2 2s2 2p6 3s2 3p6 3d10 4s 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 3d Ti4+ 1s2 2s2 2p6 3s2 3p6

26. COLOURED IONS
A characteristic of transition metals is their ability to form coloured compounds
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.

27. 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
Absorbed colour nm Observed colour nm
VIOLET GREEN-YELLOW 560
BLUE YELLOW 600
BLUE-GREEN 490 RED 620
YELLOW-GREEN 570 VIOLET 410
YELLOW DARK BLUE 430
ORANGE BLUE 450
RED GREEN 520

28. a solution of copper(II)sulphate is blue because
red and yellow wavelengths are absorbed
blue and green not absorbed
white light

29. Coordination Compound
Open Power Point Coordination Chemistry

30. A Coordination Compound
Small size d block ions tend to attract species rich in electrons forming complex ions.
Typically consists of a complex ion and counterions (anions or cations as needed to produce a neutral compound):
[Co(NH3)5Cl]Cl2
K3Fe(CN)6

31. Ligands
Neutral molecule or ion having a lone electron pair that can be used to form a bond to a metal ion.
Monodentate ligand – one bond to a metal ion
Bidentate ligand – two bonds to a metal ion
Polydentate ligand – more than two bonds to a metal ion

32. COMPLEX IONS - LIGANDS
Formation ligands form co-ordinate bonds to a central transition metal ion
Ligands atoms, or ions, which possess lone pairs of electrons
form co-ordinate bonds to the central ion
donate a lone pair into vacant orbitals on the central species
Ligand Formula Name of ligand
chloride Cl¯ chloro
cyanide NC¯ cyano
hydroxide HO¯ hydroxo
oxide O2- oxo
water H2O aqua
ammonia NH3 ammine
some ligands attach themselves using two or more lone pairs
classified by the number of lone pairs they use
multidentate and bidentate ligands lead to more stable complexes

33. some ligands attach themselves using two or more lone pairs
classified by the number of lone pairs they use
multidentate 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-

34. Coordination Number
Number of bonds formed between the metal ion and the ligands in the complex ion.
6 (octahedral shape)and 4 (tetrahedral shape)
2 and 8 (least common, linear)

35. Coordination Number: 6, 4, 2

36. when transition metals form coordination complexes, the d-orbitals of the metal interact with the electron cloud of the ligands in such a manner that the d-orbitals become non-degenerate (not all having the same energy.)
The way in which the orbitals are split into different energy levels is dependent on the geometry of the complex.

37.
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.

38. INCREASING ENERGY / DISTANCE FROM NUCLEUS
COPPER 4 4p 4d 4f
INCREASING ENERGY / DISTANCE FROM NUCLEUS 3d 4s 3 3p
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 OF
MAXIMUM MULTIPLICITY

39.
The diagram shows the arrangement of the d electrons in a Cu2+ =[Ar]3d9 before and after six water molecules bond with it.

40. 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.

41. 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.

42. 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.
OCTAHEDRAL
TETRAHEDRAL 3d 3d
The light that is absorbed corresponds to the energy required to promote a d electron from the lower split level to the higher split level

44. The magnitude of the splitting of the d-orbitals in a transition metal complex depends on three things:
the geometry(shape) of the complex
the oxidation state of the metal
the nature of the ligands

45. Complex ion - Iron
Water is a common ligand as in hexaaquairon (III) ion, [Fe(H2O)6 3+

46. COMPLEX IONS - LIGANDS
some ligands attach themselves using two or more lone pairs
classified by the number of lone pairs they use
multidentate 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

47. COMPLEX IONS - LIGANDS
some ligands attach themselves using two or more lone pairs
classified by the number of lone pairs they use
multidentate and bidentate ligands lead to more stable complexes
Multidentate form several co-ordinate bonds

48. 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]+

49. Ligands can be replaced by other ligands.
Copper and Ammonia
Ligands can be replaced by other ligands.
The addition of ammonia to an aqueous solution of copper sulfate gives a deep blue color of tetramine copperII ion.
Cl NH3
[CuCl4]2-  [Cu(H2O)4 ]2+  [Cu(NH3)4 ]2+
H2O H2O

50. 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.

51. 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)

52. 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 easily
Transition 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

54. Read CC page 59,60. Outline due Monday.

55. Co in Vitamin B12
Vitamin 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.
Cobalt is a biological catalyst.

56. 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 SO3(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.[
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:

58. Haber Process N2(g) + 3H2(g)  2NH3
The Haber Process combines nitrogen and hydrogen into ammonia. The nitrogen comes from the air and the hydrogen is obtained mainly from natural gas (methane). Iron is used as a catalyst.
N2(g) + 3H2(g)  2NH3

59. Iron in hemoglobin(iron is a biological catalyst)
A hemoglobin molecule is made up of a heme unit covalently bonded to a protein chain.
Hemes are most commonly recognized in their presence as components of hemoglobin, the red pigment in blood,

60. Decomposition of Hydrogen Peroxide – MnO2
Hydrogen peroxide decomposes to oxygen and water when a small amounts of manganese dioxide is added..
2 H2O2 → 2 H2O + O2

62. Nitrogen
Ethene reacts with hydrogen in the presence of a finely divided nickel catalyst at a temperature of about 150°C. Ethane is produced.

63. Catalytic Converter
Catalytic converters change poisonous molecules like carbon monoxide and various nitrogen oxides in car exhausts into more harmless molecules like carbon dioxide and nitrogen. They use expensive metals like platinum, palladium and rhodium as the heterogeneous catalyst.
The metals are deposited as thin layers onto a ceramic honeycomb. This maximises the surface area and keeps the amount of metal used to a minimum.

64. Catalytic Converters CO + Unburned Hydrocarbons + O2 CO2 + H2O
2NO + 2NO2
2N2 + 3O2
13.6

65. 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.
Cc page 66

66.
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.

67. So, a catalyst affects the transition state and activation path
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.