Transition Elements&Catalysts

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 DefinitionD-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

THE FIRST ROW TRANSITION ELEMENTS Metallic propertiesall 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 density / g cm

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS POTASSIUM 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 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 INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS CALCIUM 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 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 -s 1 electronic configuration are in Group I and all with an -s 2 configuration are in Group II. INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS SCANDIUM 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 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. INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS TITANIUM 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2 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 HUND’S RULE OF MAXIMUM MULTIPLICITY INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS VANADIUM 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 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 HUND’S RULE OF MAXIMUM MULTIPLICITY INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f INCREASING ENERGY / DISTANCE FROM NUCLEUS ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS CHROMIUM 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 One would expect the configuration of chromium atoms to end in 4s 2 3d 4. 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 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS MANGANESE 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 The new electron goes into the 4s to restore its filled state. INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS IRON 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 Orbitals are filled according to Hund’s Rule. They continue to pair up. HUND’S RULE OF MAXIMUM MULTIPLICITY HUND’S RULE OF MAXIMUM MULTIPLICITY INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS COBALT 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7 Orbitals are filled according to Hund’s Rule. They continue to pair up. HUND’S RULE OF MAXIMUM MULTIPLICITY HUND’S RULE OF MAXIMUM MULTIPLICITY INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS NICKEL 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8 Orbitals are filled according to Hund’s Rule. They continue to pair up. HUND’S RULE OF MAXIMUM MULTIPLICITY HUND’S RULE OF MAXIMUM MULTIPLICITY INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS COPPER 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 One would expect the configuration of copper atoms to end in 4s 2 3d 9. 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 HUND’S RULE OF MAXIMUM MULTIPLICITY INCREASING ENERGY / DISTANCE FROM NUCLEUS

4s 3 3p 3d 4 4p 4d 4f ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS ZINC 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 The electron goes into the 4s to restore its filled state and complete the 3d and 4s orbital filling. INCREASING ENERGY / DISTANCE FROM NUCLEUS

K1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 Ca1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Sc1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1 Ti1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 2 V1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 3 Cr1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 Mn1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 Fe1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 Co1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7 Ni1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8 Cu1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 Zn1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 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 Cu1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1 Ti1s 2 2s 2 2p 6 3s 2 3p 6 3d 2 4s 2 Cu + 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 Ti 2+ 1s 2 2s 2 2p 6 3s 2 3p 6 3d 2 Cu 2+ 1s 2 2s 2 2p 6 3s 2 3p 6 3d 9 Ti 3+ 1s 2 2s 2p6 3s 2 3p 6 3d 1 Ti 4+ 1s 2 2s 2 2p 6 3s 2 3p 6 maximum rises across row to manganese maximum falls as the energy required to remove more electrons becomes very high all (except scandium) have an M 2+ ion stability of +2 state increases across the row due to increase in the 3rd Ionisation Energy THE MOST IMPORTANT STATES ARE IN RED TiScVCrMnFeCoNiCuZn

COLOURED IONS Theory ions with a d 10 (full) or d 0 (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 d 10 (full) Cu +,Ag + Zn 2+ or d 0 (empty) Sc 3+ configuration are colourless e.g. titanium(IV) oxide TiO 2 is white colour depends on... transition element oxidation state ligand coordination number A characteristic of transition metals is their ability to form coloured compounds

3d ORBITALS There are 5 different orbitals of the d variety z2z2 x 2 -y 2 xyxzyz

COLOURED IONS Absorbed colournmObserved colournm VIOLET400GREEN-YELLOW560 BLUE450YELLOW600 BLUE-GREEN490RED620 YELLOW-GREEN570VIOLET410 YELLOW580DARK BLUE430 ORANGE600BLUE450 RED650GREEN520 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 because red and yellow wavelengths are absorbed white light blue 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 Ligandsatoms, 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 chlorideCl¯chloro cyanideNC¯cyano hydroxideHO¯hydroxo oxideO 2- oxo waterH 2 Oaqua ammoniaNH 3 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

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 Unidentateform one co-ordinate bond Cl¯, OH¯, CN¯, NH 3, and H 2 O Bidentateform two co-ordinate bonds H 2 NCH 2 CH 2 NH 2, C 2 O 4 2-

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 Multidentateform several co-ordinate bonds EDTA An important complexing agent

d orbitals

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 Cu 2+ 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. ns/colour.htmlhttp:// ns/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 theCENTRAL 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 OCTAHEDRALTETRAHEDRAL

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(H 2 O) 6 3+

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 Multidentateform 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 pairs classified by the number of lone pairs they use multidentate and bidentate ligands lead to more stable complexes Multidentateform 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.ShapeExample(s) 6Octahedral[Cu(H 2 O) 6 ] 2+ 4Tetrahedral [CuCl 4 ] 2- Square planarPt(NH 3 ) 2 Cl 2 2Linear[Ag(NH 3 ) 2 ] +

ISOMERISATION IN COMPLEXES GEOMETRICAL (CIS-TRANS) ISOMERISM Square planar complexes of the form [MA 2 B 2 ] n+ exist in two forms trans platincis platin An important anti-cancer drug. It is a square planar, 4 co-ordinate complex of platinum.

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.

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 easily Transition metalsTransition 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 IRONManufacture of ammonia - Haber Process NICKELHydrogenation reactions - margarine manufacture MANGANESE IV OXIDE Hydrogen peroxide VANADIUM(V) OXIDEManufacture of sulphuric acid - Contact Process

Co in Vitamin B12 Vitamin B 12, 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.vitamin brainnervous systembloodB vitaminsmetabolism cellDNAfatty acid

Contact Process Vanadium pentoxide is used in different, industrial processes as catalyst: In the contact process it serves for the oxidation of SO 2 to SO 3 with oxygen at 440°C. Sulfur dioxide and oxygen then react as follows:oxygen 2 SO 2 (g) + O 2 (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 (V 2 O 5 ) are used to ensure a 96% conversion. Platinum would be a more effective catalyst, but it is very costly and easily poisoned. [citation needed]atmvanadium(V) oxidePlatinumpoisonedcitation needed The catalyst only serves to increase the rate of reaction as it has no effect on how much SO 3 is produced. The mechanism for the action of the catalyst is: 2SO 2 + 4V O 2- → 2SO 3 + 4V 4+ 4V 4+ + O 2 → 4V O 2-

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 – MnO 2 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 H 2 O 2 → 2 H 2 O + O 2

Catalytic Converter lytic-converter2.htm

Catalytic Converters 13.6 CO + Unburned Hydrocarbons + O 2 CO 2 + H 2 O catalytic converter 2NO + 2NO 2 2N 2 + 3O 2 catalytic converter

Ostwald Process Hot Pt wire over NH 3 solution Pt-Rh catalysts used in Ostwald process 4NH 3 (g) + 5O 2 (g) 4NO (g) + 6H 2 O (g) Pt catalyst 2NO (g) + O 2 (g) 2NO 2 (g) 2NO 2 (g) + H 2 O (l) HNO 2 (aq) + HNO 3 (aq) 13.6

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.