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The First Transition Series

d & f -block. The First Transition Series. 45.1 Introduction 45.2 General Features of the d -Block Elements from Sc to Zn 45.3 Characteristic Properties of the d -Block Elements and their Compounds by : Sudhir Kumar PGT (Chem) KV 1 Pathankot.

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The First Transition Series

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  1. d & f -block The First Transition Series 45.1Introduction 45.2General Features of the d-Block Elements from Sc to Zn 45.3Characteristic Properties of the d-Block Elements and their Compounds by : Sudhir Kumar PGT (Chem) KV 1 Pathankot

  2. The first transition series

  3. Titanium Scandium Chromium Vanadium Manganese Zinc Iron Copper Cobalt Nickel Introduction • d-Block elements (transition elements): • Lie between s-block and p-block elements • Occur in the fourth and subsequent periods • All contains incomplete d sub-shell (i.e. 1 – 9 electrons) in at least one of their oxidation state

  4. Strictly speaking, scandium (Sc) and zinc (Zn) are not transitions elements • ∵ Sc forms Sc3+ ion which has an empty d sub-shell (3d0) Zn forms Zn2+ ion which has a completely filled d sub- shell (3d10)

  5. Cu shows some intermediate behaviour between transition and non-transition elements because of two oxidation states, Cu(I) & Cu(II) • Cu+ is not a transition metal ion as it has a completely filled d sub-shell • Cu2+ is a transition metal ion as it has an incompletely filled d sub-shell

  6. Relative energy levels of orbitals before and after filling with electrons General Features of the d-Block Elements from Sc to Zn Electronic Configurations

  7. General Features of the d-Block Elements from Sc to Zn • Before filling electrons, the energy of 4s sub-shell is lower than that of 3d sub-shell •  4s sub-shell is filled before 3d sub-shell • Once the 4s sub-shell is filled, the energy will increase •  The lowest energy sub-shell becomes 3d sub-shell, so the next electron is put into 3d sub-shell

  8. General Features of the d-Block Elements from Sc to Zn Electronic configurations of the first series of d-block elements

  9. General Features of the d-Block Elements from Sc to Zn • Cr is expected to be [Ar] 3d44s2 but the actual configuration is [Ar] 3d54s1 • Cu has the electronic configuration of [Ar] 3d104s1instead of [Ar] 3d94s2 • This can be explained by the fact that a half-filled or fully-filled d sub-shell provides extra stability

  10. 45.2 General Features of the d-Block Elements from Sc to Zn (SB p.167) d-Block Elements as Metals • d-block elements are typical metals • (1) good conductors of heat and electricity, hard, strong, malleable, ductile and lustrous • (2) high melting and boiling points except Hg is a liquid at room temperture • These properties make d-block elements as good construction materials • e.g. Fe is used for construction and making machinery • Ti is used to make aircraft and space shuttles

  11. General Features of the d-Block Elements from Sc to Zn ( • Transition elements have similar atomic radii which make them possible for the atom of one element to replace those of another element in the formation of alloy • e.g. Mn is for conferring hardness and wearing resistance to its alloy (duralumin) • Cr is for conferring inertness on stainless steel

  12. Tsing Ma Bridge is constructed of steel Iron is used to make ships General Features of the d-Block Elements from Sc to Zn

  13. Tungsten in a light bulb The statue is made of alloy of copper and zinc Titanium is used in making aircraft Jewellery made of gold General Features of the d-Block Elements from Sc to Zn

  14. General Features of the d-Block Elements from Sc to Zn Atomic Radii and Ionic Radii • Observations: • d-block metals have smaller atomic radii than s-block metals • The atomic radii of the d- block metals do not show much variation across the series • The atomic radii decrease initially, remain almost constant in the middle and then increase at the end of series

  15. General Features of the d-Block Elements from Sc to Zn N Variations in atomic and ionic radii of the first series of d-block elements

  16. General Features of the d-Block Elements from Sc to Zn • The atomic size reduces at the beginning of the series • ∵ increase in effective nuclear charge with atomic numbers •  the electron clouds are pulled closer to the nucleus •  causing a reduction in atomic size • The atomic size decreases slowly in the middle of the series • ∵ when more and more electrons enter the inner 3d sub-shell •  the screening and repulsive effects of the electrons in the 3d sub-shell increase •  the effective nuclear charge increases slowly

  17. General Features of the d-Block Elements from Sc to Zn • The atomic size increases at the end of the series • ∵ the screening and repulsive effects of the 3d electrons reach a maximum • The reasons for the trend of the ionic radii of the d-block elements are similar to those for the atomic radii. • Remember that the electrons have to be removed from the 4s orbital first

  18. General Features of the d-Block Elements from Sc to Zn Comparison of Some Physical and Chemical Properties between d-Block and s-Block Metals Density Densities (in g cm-3) of the s-block metals and the first series of d-block metals

  19. General Features of the d-Block Elements from Sc to Zn • d-block metals are generally denser than the s-block because most of the d-block metals have close-packed structures while most of the s-block metals do not. • The densitiesincrease generally across the first series of d-block metals. This is in agreement with the general decrease in atomic radius across the series

  20. General Features of the d-Block Elements from Sc to Zn Ionization Enthalpy

  21. General Features of the d-Block Elements from Sc to Zn • 1st I.E. of d-block metals are greaterthan those ofs-block elements in the same row of the Periodic Table. • ∵ the d-block metals are smaller in size than the s-block metals, thus they have greater effective nuclear charges • For K, the 2nd I.E. is exceptionally higher than its 1st I.E • For Ca, the 3rd I.E. is exceptionally higher than its 2nd I.E • ∵ the electrons are come form the inner fully-filled electron shells

  22. General Features of the d-Block Elements from Sc to Zn • The first few successive I.E. for d-block elements do not show dramatic changes∵ removal of electrons does not involvethe disruption of inner electron shells • The 1st I.E. of the d-block metals increase slightly and irregularly across the series • ∵ Going across the first transition series, the nuclear charge of the elements increases, and additional electrons are found in the inner 3d sub-shell •  The additional screening effect of the additional 3d electrons is so significant that the effective nuclear charge of the elements increases only very slowly across the series

  23. General Features of the d-Block Elements from Sc to Zn • Successive ionization enthalpies exhibit a similar gradual increase across the first transition series • The increases in the 3rd and 4th ionization enthalpies across the series are progressively more rapid

  24. General Features of the d-Block Elements from Sc to Zn • Some abnormal high ionization enthalpy, e.g. 1st I.E. of Zn, 2nd I.E. of Cr & Cu and the 3rd I.E. of Mn • ∵The removal of an electron from a fully-filled or half-filled sub-shell requires a relatively large amount of energy Variation of successive ionization enthalpies of the first series of the d-block elements

  25. (a) The second ionization enthalpies of both Cr and Cu are higher than those of their next elements respectively. In the case of Cr, the second ionization enthalpy involves the removal of an electron from a half-filled 3d sub-shell, which has extra stability. Therefore, this second ionization enthalpy is relatively high. The case is similar for copper where its second ionization enthalpy involves the removal of an electron from a fully-filled 3d sub-shell which also has extra stability. Thus, its second ionization enthalpy is also relatively high. General Features of the d-Block Elements from Sc to Zn Check Point 45-1 Explain the following variation in terms of electronic configurations. (a) The second ionization enthalpies of both Cr and Cu are higher than those of their next elements respectively. Answer

  26. (b) The third ionization enthalpy of Mn is higher than that of its next element. It is because its third ionization enthalpy involves the removal of an electron from a half-filled 3d sub-shell which has extra stability. Therefore, its third ionization enthalpy is relatively high. General Features of the d-Block Elements from Sc to Zn Explain the following variation in terms of electronic configurations. (b) The third ionization enthalpy of Mn is higher than that of its next element. Answer

  27. General Features of the d-Block Elements from Sc to Zn Electronegativity Electronegativity values of the s-block metals and the first series of the d-block metals

  28. General Features of the d-Block Elements from Sc to Zn • The electronegativity of d-block metals are generally higher than those of the s-block metals • ∵ Generally, d-block metals have smaller atomic radii than s-block metals the nuclei of d-block metals can attract the electrons in a bond more tightly towards themselves

  29. General Features of the d-Block Elements from Sc to Zn • The electronegativity shows a slight increase generally with increasing atomic numbers across the series • ∵ Gradual increase in effective nuclear charge and decrease in atomic radius across the series •  The closer the electron shell to the nucleus, the more strongly the additional electron in a bond is attracted Higher electronegativity

  30. General Features of the d-Block Elements from Sc to Zn Melting Point and Hardness Melting points (C) of the s-block metals and the first series of the d-block metals

  31. General Features of the d-Block Elements from Sc to Zn • The melting points of the d-block metals are muchhigher than those of the s-block metals • Reasons: • 1.d-block metal atoms are small in size and closely packed in the metallic lattice. All Group I metals and some Group II metals do not have close-packed structures • 2. Both 3d and 4s electrons of d-block metals participate in metallic bonding by delocalizing into the electron sea, and thus the metallic bond strength is very strongs-Block metals have only 1 to 2 valence electrons per atom delocalizing into the electron sea

  32. General Features of the d-Block Elements from Sc to Zn • The hardness of a metal depends on thestrength of the metallic bonds • ∵ The metallic bond of d-block metals is stronger than that of s-block metals •  d-block metals are much harder than the s-block metals

  33. The d-block metals are comparatively small, and the metallic atoms are closely packed in the metallic lattice. Besides, both the 3d and 4s electrons of the d-block metals participate in metallic bonding by delocalizing into the electron sea. The strength of metallic bond in these metals is thus very strong. In the case of s-block metals, the metallic radius is larger and most of them do not have close-packed structures. Also , as they have only one or two valence electrons per atom delocalizing into the electron sea, the metallic bond formed is weaker. Therefore, the d-block metals have a much higher melting point than the s-block metals. General Features of the d-Block Elements from Sc to Zn Check Point 45-2 What are the differences between the structures and bonding of the d-block and s-block metals? How do these differences affect their melting points? Answer

  34. Generally, s-block metals (e.g. K, Na & Ca) react with H2O vigorously to form metal hydroxides and H2 • d-block metals react only very slowly with cold water.Zn and Fe are relatively more reactive •  Zn and Fe react with steam to give metal oxides and H2 • Zn(s) + H2O(g)  ZnO(s) + H2(g) • 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g) General Features of the d-Block Elements from Sc to Zn ( Reaction with Water

  35. 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.175) Variable Oxidation States • d-block elements has ability to show variable oxidation states • ∵ 3d & 4s electrons are of similar energy levels, the electrons in both of them are available for bonding •  When the first transition elements react to form compounds, they can form ions of roughly the same stability by losing different numbers of electrons •  Form compounds with a wide variety of oxidation states

  36. 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.175) Oxidation states of the elements of the first transition series in their oxides and chlorides

  37. 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.176) Oxidation states of the elements of the first transition series in their compounds

  38. 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.176) Observations: 1. Sc and Zn do not exhibit variable oxidation states. Sc3+ has electronic configuration of argon (i.e. 1s22s22p63s23p6). Zn2+ has the electronic configuration of [Ar] 3d10. Other oxidation states are not possible. 2. Except Sc, all elements have +2 oxidation state. Except Zn, all elements have +3 oxidation state 3. The highest oxidation state is +7 at Mn. This corresponds to removal of all 3d & 4s electrons. (Note: max.oxidation state is NEVER greater than the total number of 3d & 4s electrons)

  39. 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.176) 4. There is a reduction in the number of oxidation states after Mn. ∵ decreasein the number of unpaired electrons and increase in nuclear charge which holds the 3d electrons more firmly 5. The relative stability of various oxidation states can be correlated -with the stability of empty, half-filled and fully- filled configuration e.g. Ti4+ is more stable than Ti3+ (∵ [Ar]3d0 configuration) Mn2+ is more stable than Mn3+ (∵ [Ar]3d5 configuration) Zn2+ is more stable than Zn+ (∵ [Ar]3d10 configuration)

  40. 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.177) Variable Oxidation States of Vanadium and their Interconversions • Vanadium shows oxidation states from +2 to +5 in its compounds • In these oxidation state, vanadium forms ions which have distinctive colours in aqueous solutions

  41. 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.177) • In acidic medium, vanadium(V) state occurs as VO2+(aq); vanadium(IV) state occurs as VO2+(aq) • In alkaline medium, vanadium(V) state occurs as VO3–(aq) • Most compounds with vanadium(V) are good oxidizing agents while those with vanadium(II) are good reducing agents • The starting material for the interconversions of common oxidation states of vanadium is ammonium vanadate(V) (NH4VO3) • When NH4VO3 is acidified, vanadium exists in the form of VO2+(aq) which the oxidation state of +5

  42. Vanadium(V) ions can be reduced sequentially to vanadium(II) ions by the action of Zn powder and acid • The sequence of color changes forms a characteristic test for vanadium • VO2+(aq)  VO2+(aq)  V3+(aq)  V2+(aq) Zn conc. HCl Zn conc. HCl Zn conc. HCl violet yellow blue green 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.177)

  43. Half reaction E (V) Zn2+(aq) + 2e– Zn(s) VO2+(aq) + 2H+(aq) + e– VO2+(aq) + H2O(l) VO2+(aq) + 2H+(aq) + e– V3+(aq) + H2O(l) V3+(aq) + e– V2+(aq) –0.76 +1.00 +0.34 –0.26 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.178) • The feasibility of the changes in oxidation number of vanadium can be predicted by using electrode potentials easily

  44. Under standard conditions, Zn can reduce vanadium(V) to vanadium(IV) as the Ecell value is +ve • 2  (VO2+(aq) + 2H+(aq) + e– VO2+(aq) + H2O(l))E = +1.00 V–) Zn2+(aq) + 2e– Zn(s) E = –0.76 V • 2VO2+(aq) + Zn(s) + 4H+(aq) 2VO2+(aq) + Zn2+(aq) + 2H2O(l) Ecell = +1.76 V 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.178)

  45. Further reduction of vanadium(IV) to vanadium(III) by Zn is feasible as the Ecell value is +ve • 2  (VO2+(aq) + 2H+(aq) + e– V3+(aq) + H2O(l))E = +0.34 V–) Zn2+(aq) + 2e– Zn(s) E = –0.76 V • 2VO2+(aq) + Zn(s) + 4H+(aq) 2V3+(aq) + Zn2+(aq)+ 2H2O(l) Ecell = +1.10 V 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.178)

  46. Further reduction of vanadium(III) to vanadium(II) by Zn is also feasible • 2  (V3+(aq) + e– V2+(aq))E = +0.34 V–) Zn2+(aq) + 2e– Zn(s) E = –0.76 V • 2V3+(aq) + Zn(s) 2V2+(aq) + Zn2+(aq) Ecell = +0.50 V 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.179) Conclusion: Zn acts as a strong reducing agent which reduces vanadium(V) through vanadium(IV), vanadium(III)and finally to vanadium(II) in an acidic medium

  47. 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.179) Variable Oxidation States of Manganese and their Interconversions • Mn shows oxidation states from +2 to +7 in its compounds • The most common oxidation states of Mn include +2, +4, +7 • Mn also forms coloured compoundsor ions in these oxidation states

  48. Mn is most stable in +2 oxidation state • The most common Mn compound in +4 oxidation state is MnO2 which is a strong oxidizing agent. It reacts with reducing agents and is reduced to Mn2+ • MnO2(s) + 4H+(aq) + 2e– • Mn2+(aq) + 2H2O(l) E = +1.23 V • MnO2 is used in the laboratory production of chlorine • MnO2(s) + 4HCl(aq)  MnCl2(aq) + 2H2O(l) + Cl2(g) +4 black +2 very pale pink 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.179)

  49. The most common Mn compound in +7 oxidation state is KMnO4 which is an extremely powerful oxidizing agent. Its oxidizing power depends on pH • In acidic medium, MnO4– ions are reduced to Mn2+ ions • MnO4–(aq) + 8H+(aq) + 5e– Mn2+(aq) + 4H2O(l) • E = +1.23 V +7 purple +2 very pale pink • In alkaline medium, MnO4– ions are reduced to MnO2 • MnO4–(aq) + 2H2O(l) + 3e– MnO2(s) + 4OH–(aq) • E = +0.59 V +7 purple +4 black 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.180)

  50. Mn(II) Mn(IV) Mn(VII) Mn(III) Mn(VI) 45.3 Characteristic Properties of the d-Block Elements and their Compounds (SB p.180)

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