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AN INTRODUCTION TO TRANSITION METAL CHEMISTRY KNOCKHARDY PUBLISHING KNOCKHARDY PUBLISHING TRANSITION METALS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard TRANSITION METALS CONTENTS • Definition • Metallic properties • Electronic configurations • Variable oxidation state • Coloured ions • Complex ion formation • Shapes of complexes • Isomerism in complexes • Catalytic properties • Revision check list TRANSITION METALS Before you start it would be helpful to… • Recall the definition of a co-ordinate (dative covalent) bond • Recall how to predict the shapes of simple molecules and ions 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 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 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 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 ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS POTASSIUM INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS CALCIUM INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS SCANDIUM INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS TITANIUM INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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 ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS VANADIUM INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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 ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS CHROMIUM INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS MANGANESE INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 3d 4s 3 3p 1s2 2s2 2p6 3s2 3p6 4s2 3d5 The new electron goes into the 4s to restore its filled state. ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS IRON INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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 ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS COBALT INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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 ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS NICKEL INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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 ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS COPPER INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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 ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS ZINC INCREASING ENERGY / DISTANCE FROM NUCLEUS 4f 4 4d 4p 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. 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 VARIABLE OXIDATION STATES Arises from the similar energies required for removal of 4s and 3d electrons maximum rises across row to manganese Sc Ti V Cr Mn Fe Co Ni +7 maximum falls as the energy required to remove more electrons becomes very high +6 +6 +6 +5 +5 +5 +5 all (except scandium) have an M2+ ion stability of +2 state increases across the row due to increase in the 3rd Ionisation Energy Cu Zn +4 +4 +4 +3 +3 +2 +3 +3 +2 +4 +4 +5 +4 +4 +3 +3 +3 +2 +2 +2 +2 +3 +2 +2 +2 +1 THE MOST IMPORTANT STATES ARE IN RED When electrons are removed they come from the 4s orbitals first Cu Cu+ Cu2+ 1s2 2s2 2p6 3s2 3p6 3d10 4s1 1s2 2s2 2p6 3s2 3p6 3d10 1s2 2s2 2p6 3s2 3p6 3d9 Ti Ti2+ Ti3+ Ti4+ 1s2 2s2 2p6 3s2 3p6 3d2 4s2 1s2 2s2 2p6 3s2 3p6 3d2 1s2 2s 2p6 3s2 3p6 3d1 1s2 2s2 2p6 3s2 3p6 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 ions with or d10 (full) Cu+,Ag+ Zn2+ d0 (empty) Sc3+ configuration are colourless e.g. titanium(IV) oxide TiO2 is white colour depends on ... transition element oxidation state ligand coordination number 3d ORBITALS There are 5 different orbitals of the d variety xy xz x2-y2 yz z2 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 (z2 and x2-y2) go higher and three go lower In a tetrahedral complex, three (xy, xz and yz) go higher and two go lower OCTAHEDRAL TETRAHEDRAL 3d 3d 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. COLOURED IONS 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 VIOLET BLUE BLUE-GREEN YELLOW-GREEN YELLOW ORANGE RED nm 400 450 490 570 580 600 650 Observed colour GREEN-YELLOW YELLOW RED VIOLET DARK BLUE BLUE GREEN nm 560 600 620 410 430 450 520 COLOURED IONS a solution of copper(II)sulphate is blue because red and yellow wavelengths are absorbed white light blue and green not absorbed COLOURED IONS a solution of copper(II)sulphate is blue because red and yellow wavelengths are absorbed COLOURED IONS a solution of copper(II)sulphate is blue because red and yellow wavelengths are absorbed COLOURED IONS a solution of nickel(II)sulphate is green because violet, blue and red wavelengths are absorbed FINDING COMPLEX ION FORMULAE USING COLORIMETRY • • • • • • a change of ligand can change the colour of a complex this property can be used to find the formula of a complex ion ight of a certain wavelength is passed through a solution the greater the colour intensity, the greater the absorbance the concentration of each species in the complex is altered the mixture with the greatest absorbance identifies ratio of ligands and ions RED LIGHT WHITE LIGHT BLUE FILTER SOLUTION COLORIMETER FINDING COMPLEX ION FORMULAE USING COLORIMETRY • • • • • • a change of ligand can change the colour of a complex this property can be used to find the formula of a complex ion Light of a certain wavelength is passed through a solution the greater the colour intensity, the greater the absorbance the concentration of each species in the complex is altered the mixture with the greatest absorbance identifies ratio of ligands and ions Finding the formula of an iron(III) complex White light is passed through a blue filter. The resulting red light is passed through mixtures of an aqueous iron(III) and potassium thiocyanate solution. Maximum absorbance occurs first when the ratio of Fe3+ and SCN¯ is 1:1. This shows the complex has the formula [Fe(H2O)5SCN]2+ FINDING COMPLEX ION FORMULAE USING COLORIMETRY • • • • • • a change of ligand can change the colour of a complex this property can be used to find the formula of a complex ion ight of a certain wavelength is passed through a solution the greater the colour intensity, the greater the absorbance the concentration of each species in the complex is altered the mixture with the greatest absorbance identifies ratio of ligands and ions Finding the formula of an nickel(II) edta complex Filtered light is passed through various mixtures of an aqueous solution of nickel(II) sulphate and edta solution. The maximum absorbance occurs when the ratio of Ni2+ and edta is 1:1. 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 chloride cyanide hydroxide oxide water ammonia Formula Cl¯ NC¯ HO¯ O2H2O NH3 Name of ligand chloro cyano hydroxo oxo aqua 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 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 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 EDTA An important complexing agent 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 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 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- 2 Square planar Pt(NH3)2Cl2 Linear [Ag(NH3)2]+ ISOMERISATION IN COMPLEXES Some octahedral complexes can exist in more than one form [MA4B2]n+ TRANS [MA3B3]n+ CIS ISOMERISATION IN COMPLEXES GEOMETRICAL 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. ISOMERISATION IN COMPLEXES OPTICAL ISOMERISM Some octahedral complexes exist in two forms Octahedral complexes with bidentate ligands can exist as a pair of enantiomers (optical isomers) 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 Examples of catalysts IRON Manufacture of ammonia - Haber Process NICKEL Hydrogenation reactions - margarine manufacture RHODIUM Catalytic converters VANADIUM(V) OXIDE Manufacture of sulphuric acid - Contact Process REVISION CHECK What should you be able to do? Recall and explain the typical properties of transition metals and their ions Recall and explain the electronic configurations of the first row transition elements Recall and explain the origin of colour in compounds and complex ions Recall and explain the shape of complex ions Recall and explain the possibilities for isomerism in complexes Recall examples of catalysis involving transition metals and their compounds CAN YOU DO ALL OF THESE? YES NO You need to go over the relevant topic(s) again Click on the button to return to the menu WELL DONE! Try some past paper questions AN INTRODUCTION TO TRANSITION METAL CHEMISTRY THE END © JONATHAN HOPTON & KNOCKHARDY PUBLISHING
