Computer science 12th DOC-20240924-WA0006.pptx

Computer class 12th

1. The d -Block Elements

2. Introduction d -block elements 🡺 locate between the s -block and p -block 🡺 known as transition elements 🡺 occur in the fourth and subsequent periods of the Periodic Table

3. period 4 period 5 period 6 period 7 d-block elements

4. Introduction Transition elements are elements that contain an incomplete d sub-shell (i.e. d 1 to d 9 ) in at least one of their oxidation states in compounds. 3d 3d 10

5. Introduction Cd and Zn are not transition elements because They form compounds with only one oxidation state in which the d sub-shell are NOT incomplete. Cd → Cd 2+ 4d 10 Zn → Zn 2+ 3d 10

6. The first transition series the first horizontal row of the d -block elements

7. Characteristics of transition elements (d-block vs s-block) Physical properties vary slightly with atomic number across the series (cf. s-block and p-block elements) Higher m.p./b.p./density/hardness than s-block elements of the same periods. Variable oxidation states (cf. fixed oxidation states of s-block elements)

8. Characteristics of transition elements 4. Formation of coloured compounds/ions (cf. colourless ions of s-block elements) 5. Formation of complexes 6. Catalytic properties

9. The building up of electronic configurations of elements: 🡺 Aufbau principle 🡺 Pauli exclusion principle 🡺 Hund’s rule Electronic Configurations

10. 3d and 4s sub-shells are very close to each other in energy. Relative energy of electrons in sub-shells depends on the effective nuclear charge they experience. Electrons enter 4s sub-shell first Electrons leave 4s sub-shell first Electronic Configurations

11. Cu Cu 2+ After ‘electrons’ left the atom Relative energy levels of orbitals in atom and in ion

12. Valence electrons in the inner 3 d orbitals Electronic Configurations Examples: 🡺 The electronic configuration of scandium: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 1 4 s 2 🡺 The electronic configuration of zinc: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 3 d 10 4 s 2

13. Element Atomic number Electronic configuration Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc 21 22 23 24 25 26 27 28 29 30 [Ar] 3 d 1 4 s 2 [Ar] 3 d 2 4 s 2 [Ar] 3 d 3 4 s 2 [Ar] 3 d 5 4 s 1 [Ar] 3 d 5 4 s 2 [Ar] 3 d 6 4 s 2 [Ar] 3 d 7 4 s 2 [Ar] 3 d 8 4 s 2 [Ar] 3 d 10 4 s 1 [Ar] 3 d 10 4 s 2 Electronic configurations of the first series of the d -block elements

14. A half-filled or fully-filled d sub-shell has extra stability

15. d -Block Elements as Metals Physical properties of d -Block elements : 🡺 good conductors of heat and electricity 🡺 hard 🡺 strong 🡺 malleable and ductile d -Block elements are typical metals

16. d -Block Elements as Metals Physical properties of d -Block elements: 🡺 lustrous 🡺 high melting points and boiling points Exceptions : Mercury 🡺 low melting point 🡺 liquid at room temperature and pressure

17. d -Block Elements as Metals d -block elements 🡺 extremely useful as construction materials  strong and unreactive

18. d -Block Elements as Metals 🡺 used for construction and making machinery nowadays 🡺 abundant 🡺 easy to extract Iron

19. d -Block Elements as Metals Iron 🡺 corrodes easily 🡺 often combined with other elements to form steel ∴ harder and higher resistance to corrosion

20. d -Block Elements as Metals Titanium 🡺 used to make aircraft and space shuttles 🡺 expensive Corrosion resistant, light, strong and withstand large temperature changes

21. d -Block Elements as Metals The similar atomic radii of the transition metals facilitate 🡺 formation of substitutional alloys 🡺 the atoms of one element to replace those of another element 🡺 modify their solid structures and physical properties

22. d -Block Elements as Metals Manganese confers hardness & wearing resistance to its alloys e.g. duralumin : alloy of Al with Mn/Mg/Cu Chromium 🡺 confers inertness to stainless steel

23. Atomic Radii and Ionic Radii Two features can be observed: 1. The d -block elements have smaller atomic radii than the s -block elements 2. The atomic radii of the d -block elements do not show much variation across the series

24. Variation in atomic radius of the first 36 elements Atomic Radii and Ionic Radii

25. (i) ↑ in nuclear charge (ii) ↑ in shielding effect (repulsion between e - ) (i) > (ii) (i) ≈ (ii) (ii) > (i)

26. At the beginning of the series 🡺 atomic number ↑ 🡺 effective nuclear charge ↑ 🡺 the electron clouds are pulled closer to the nucleus 🡺 atomic size ↓ Atomic Radii and Ionic Radii

27. In the middle of the series 🡺 the effective nuclear charge experienced by 4s electrons increases very slowly 🡺 only a slow decrease in atomic radius in this region 🡺 more electrons enter the inner 3 d sub-shell 🡺 The inner 3d electrons shield the outer 4s electrons effectively

28. At the end of the series 🡺 the screening and repulsive effects of the electrons in the 3 d sub- shell become even stronger 🡺 Atomic size ↑ Atomic Radii and Ionic Radii

29. Many of the differences in physical and chemical properties between the d -block and s -block elements 🡺 explained in terms of their differences in electronic configurations and atomic radii Comparison of Some Physical and Chemical Properties between the d -Block and s -Block Elements

30. 1. Density Densities (in g cm –3 ) of the s -block elements and the first series of the d -block elements at 20°C

31. d -block > s -block  1. the atoms of the d -block elements are generally smaller in size 2. more closely packed (fcc/hcp vs bcc in group 1) 3. higher atomic mass 1. Density

32. The densities 🡺 generally increase across the first series of the d -block elements  1. general decrease in atomic radius across the series 2. general increase in atomic mass across the series 1. Density

33. 2. Ionization Enthalpy Element Ionization enthalpy (kJ mol –1 ) 1st 2nd 3rd 4th K Ca 418 590 3 070 1 150 4 600 4 940 5 860 6 480 Sc Ti V Cr 632 661 648 653 1 240 1 310 1 370 1 590 2 390 2 720 2 870 2 990 7 110 4 170 4 600 4 770 K → Ca (sharp ↑) ; Ca → Sc (slight ↑)

34. 2. Ionization Enthalpy Element Ionization enthalpy (kJ mol –1 ) 1st 2nd 3rd 4th Cr Mn Fe Co Ni Cu Zn 653 716 762 757 736 745 908 1 590 1 510 1 560 1 640 1 750 1 960 1 730 2 990 3 250 2 960 3 230 3 390 3 550 3 828 4 770 5 190 5 400 5 100 5 400 5 690 5 980 Sc → Cu (slight ↑) ; Cu → Zn (sharp ↑)

35. The first ionization enthalpies of the d -block elements 🡺 greater than those of the s -block elements in the same period of the Periodic Table  1. The atoms of the d -block elements are smaller in size 2. greater effective nuclear charges 2. Ionization Enthalpy

36. Sharp ↑ across periods 1, 2 and 3 Slight ↑ across the transition series

37. Going across the first transition series 🡺 the nuclear charge of the elements increases 🡺 additional electrons are added to the ‘inner’ 3 d sub-shell 2. Ionization Enthalpy

38. The screening effect of the additional 3 d electrons is significant 2. Ionization Enthalpy The effective nuclear charge experienced by the 4s electrons increases very slightly across the series For 2 nd , 3 rd , 4 th … ionization enthalpies, similar gradual ↑ across the series are observed.

39. Electron has to be removed from completely filled 3p subshell 3d 5 3d 5 3d 5 3d 10 d 10 /s 2

40. The first few successive ionization enthalpies for the d -block elements 🡺 do not show dramatic changes  4s and 3d energy levels are close to each other 2. Ionization Enthalpy

41. Difficult to remove e - from fully- or half-filled sub-shells d 5 Cr + Mn 2+ Fe 3+

42. 3. Melting Points and Hardness 1541 1668 1910 1907 1246 1538 1495 1455 1084 419 d-block >> s-block  1. both 4s and 3d e - are involved in the formation of metal bonds 2. d-block atoms are smaller

43. 3. Melting Points and Hardness K has an exceptionally small m.p. because it has an more open b.c.c. structure. 1541 1668 1910 1907 1246 1538 1495 1455 1084 419

44.  Unpaired electrons are relatively more involved in the sea of electrons Sc Ti V Cr Mn Fe Co Ni Cu Zn 1541 1668 1910 1907 1246 1538 1495 1455 1084 419

45. ↑ ↑↓ 3d 4s Sc ↑ ↑ ↑↓ Ti ↑ ↑ ↑ ↑↓ V m.p. ↑ from Sc to V due to the ↑ of unpaired d-electrons (from d 1 to d 3 ) Sc Ti V Cr Mn Fe Co Ni Cu Zn 1541 1668 1910 1907 1246 1538 1495 1455 1084 419

46. 2. m.p. ↓ from Fe to Zn due to the ↓ of unpaired d-electrons (from 4 to 0) Sc Ti V Cr Mn Fe Co Ni Cu Zn 1541 1668 1910 1907 1246 1538 1495 1455 1084 419 ↑↓ ↑ ↑ ↑ ↑ ↑↓ 3d 4s Fe ↑↓ ↑↓ ↑ ↑ ↑ ↑↓ Co ↑↓ ↑↓ ↑↓ ↑ ↑ ↑↓ Ni

47. Sc Ti V Cr Mn Fe Co Ni Cu Zn 1541 1668 1910 1907 1246 1538 1495 1455 1084 419 3. Cr has the highest no. of unpaired electrons but its m.p. is lower than V. ↑ ↑ ↑ ↑ ↑ ↑ 3d 4s Cr It is because the electrons in the half-filled d-subshell are relatively less involved in the sea of electrons.

48. Sc Ti V Cr Mn Fe Co Ni Cu Zn 1541 1668 1910 1907 1246 1538 1495 1455 1084 419 4. Mn has an exceptionally low m.p. because it has the very open cubic structure. Why is Hg a liquid at room conditions ? All 5d and 6s electrons are paired up and the size of the atoms is much larger than that of Zn.

49. The metallic bonds of the d -block elements are stronger than those of the s -block elements ∴ much harder than the s -block elements 3. Melting Points and Hardness The hardness of a metal dependent on 🡺 the strength of the metallic bonds

50. Mohs scale : - A measure of hardness Talc Diamond 10 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn 0.5 1.5 3.0 4.5 6.1 9.0 5.0 4.5 -- -- 2.8 2.5

51. In general, the s -block elements 🡺 react vigorously with water to form metal hydroxides and hydrogen 4. Reaction with Water The d -block elements 🡺 react very slowly with cold water 🡺 react with steam to give metal oxides and hydrogen

52. d-block compounds vs s-block compounds A Summary : - Ions of d-block metals have higher charge density ⇒ more polarizing ⇒ 1. more covalent in nature 2. less soluble in water 3. less basic (more acidic) e.g. Fe(OH) 3 < Fe(OH) 2 << NaOH

53. One of the most striking properties 🡺 variable oxidation states Variable Oxidation States The 3 d and 4 s electrons are 🡺 in similar energy levels 🡺 available for bonding

54. Elements of the first transition series 🡺 react with other elements to form compounds 🡺 form ions of roughly the same stability by losing different numbers of the 3 d and 4 s electrons Variable Oxidation States

55. Oxidation states Oxides / Chloride +1 Cu 2 O Cu 2 Cl 2 +2 TiO VO CrO MnO FeO CoO NiO CuO ZnO TiCl 2 VCl 2 CrCl 2 MnCl 2 FeCl 2 CoCl 2 NiCl 2 CuCl 2 ZnCl 2 +3 Sc 2 O 3 Ti 2 O 3 V 2 O 3 Cr 2 O 3 Mn 2 O 3 Fe 2 O 3 Ni 2 O 3 • x H 2 O ScCl 3 TiCl 3 VCl 3 CrCl 3 MnCl 3 FeCl 3 +4 TiO 2 VO 2 MnO 2 TiCl 4 VCl 4 CrCl 4 +5 V 2 O 5 +6 CrO 3 +7 Mn 2 O 7 Oxidation states of the elements of the first transition series in their oxides and chlorides

56. Oxidation states of the elements of the first transition series in their compounds Element Possible oxidation state Sc Ti V Cr Mn Fe Co Ni Cu Zn Element Possible oxidation state Sc Ti V Cr Mn Fe Co Ni Cu Zn +3 +1 +2 +3 +4 +1 +2 +3 +4 +5 +1 +2 +3 +4 +5 +6 +1 +2 +3 +4 +5 +6 +7 +1 +2 +3 +4 +5 +6 +1 +2 +3 +4 +5 +1 +2 +3 +4 +5 +1 +2 +3 +2

57. 1. Scandium and zinc do not exhibit variable oxidation states Scandium of the oxidation state +3 🡺 the stable electronic configuration of argon (i.e. 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 ) Zinc of the oxidation state +2 🡺 the stable electronic configuration of [Ar] 3 d 10

58. 2. (a) All elements of the first transition series (except Sc) can show an oxidation state of +2 (b) All elements of the first transition series (except Zn) can show an oxidation state of +3

59. 3. Manganese has the highest oxidation state +7 E.g. MnO 4 - , Mn 2 O 7 Mn 7+ ions do not exist.

60. The +7 state of Mn does not mean that all 3d and 4s electrons are removed from Mn to give Mn 7+ . Instead, Mn forms covalent bonds with oxygen atoms by making use of its half filled orbitals

61. Draw the structure of Mn 2 O 7

62. 3. Manganese has the highest oxidation state +7 The highest oxidation state 🡺 not be greater than the total number of the 3 d and 4 s electrons  inner electrons (3s, 3p…) are not involved in covalent bond formation

63. 4. For elements after manganese, there is a reduction in the number of possible oxidation states The 3 d electrons are held more firmly  the decrease in the number of unpaired electrons  the increase in nuclear charge

64. 5. The relative stability of various oxidation states is correlated with the stability of electronic configurations Electronic configurations with half-filled or fully-filled sub-shell has extra stability Stability : - Ti 4+ (aq) > Ti 3+ (aq) Ar [Ar] 3d 1 Ti 4+ (g) < Ti 3+ (g) : Ti 4+ > Ti 3+

65. 5. The relative stability of various oxidation states is correlated with the stability of electronic configurations Stability : - Mn 2+ (aq) > Mn 3+ (aq) [Ar] 3 d 5 [Ar] 3 d 4 Fe 3+ (aq) > Fe 2+ (aq) [Ar] 3 d 5 [Ar] 3 d 6

66. 5. The relative stability of various oxidation states is correlated with the stability of electronic configurations Stability : - Zn 2+ (aq) > Zn + (aq) [Ar] 3d 10 [Ar] 3d 10 4s 1

67. Ion Oxidation state of vanadium in the ion Colour in aqueous solution V 2+ (aq) V 3+ (aq) VO 2+ (aq) VO 2 + (aq) +2 +3 +4 +5 Violet Green Blue Yellow Colours of aqueous ions of vanadium of different oxidation states

68. Ion Oxidation state of manganese in the ion Colour Mn 2+ Mn(OH) 3 Mn 3+ MnO 2 MnO 4 2– MnO 4 – +2 +3 +3 +4 +6 +7 Very pale pink Dark brown Red Black Green Purple Colours of compounds or ions of manganese in different oxidation states

69. (a) Colours of compounds or ions of manganese in differernt oxidation states: (a) +2; (b) +3; (c) +4 (b) (c) Mn 2+ (aq) Mn(OH) 3 (aq) MnO 2 (s)

70. (e) (d) Colours of compounds or ions of manganese in differernt oxidation states: (d) +6; (e) +7 MnO 4 2– (aq) MnO 4 – (aq)

71. Oxidizing power of Mn(VII) depends on pH of the solution In an acidic medium (pH 0) MnO 4 – (aq) + 8H + (aq) + 5e – Mn 2+ (aq) + 4H 2 O(l) = +1.51 V In an alkaline medium (pH 14) MnO 4 – (aq) + 2H 2 O(l) + 3e – MnO 2 (s) + 4OH − (aq) = +0.59 V

72. The reaction does not involve H + (aq) nor OH − (aq) Why is the E o of MnO 4 − MnO 4 2− E o = +0.56V not affected by pH ? MnO 4 − (aq) + e − MnO 4 2− E o = +0.56V

73. MnO 2 is oxidized to MnO 4 2− in alkaline medium 2MnO 2 + 4OH − + O 2 → 2MnO 4 2− + 2H 2 O Preparing MnO 4 − from MnO 2 1. 2MnO 2 + 4OH − + O 2 → 2MnO 4 2− + 2H 2 O 2. 3MnO 4 2− + 4H + → 2MnO 4 − + MnO 2 + 2H 2 O 3. Filter the resulting mixture to remove MnO 2

74. Another striking feature of the d -block elements is the formation of complexes Formation of Complexes

75. Most of the d -block metals 🡺 form coloured compounds Coloured Ions 🡺 due to the presence of the i ncompletely filled d orbitals in the d -block metal ions Zn 2+ , Cu + (3d 10 ), Sc 3+ , Ti 4+ (3d ) Which aqueous transition metal ion(s) is/are not coloured ?

76. Number of unpaired electrons in 3 d orbitals d -Block metal ion Colour in aqueous solution Sc 3+ Ti 4+ Zn 2+ Cu + Colourless Colourless Colourless Colourless 1 Ti 3+ V 4+ Cu 2+ Purple Blue Blue Colours of some d -block metal ions in aqueous solutions

77. Number of unpaired electrons in 3 d orbitals d -Block metal ion Colour in aqueous solution 2 V 3+ Ni 2+ Green Green 3 V 2+ Cr 3+ Co 2+ Violet Green Pink Colours of some d -block metal ions in aqueous solutions

78. Number of unpaired electrons in 3 d orbitals d -Block metal ion Colour in aqueous solution 4 Cr 2+ Mn 3+ Fe 2+ Blue Violet Green 5 Mn 2+ Fe 3+ Very pale pink Yellow Colours of some d -block metal ions in aqueous solutions

79. Colours of some d -block metal ions in aqueous solutions Co 2+ (aq) Fe 3+ (aq) Zn 2+ (aq)

80. In gaseous state, the five 3 d orbitals are degenerate i.e. they are of the same energy level In the presence of ligands, The five 3d orbitals interact with the orbitals of ligands and split into two groups of orbitals with slightly different energy levels

81. The splitting of the degenerate 3 d orbitals of a d -block metal ion in an octahedral complex distributes along x and y axes distributes along z axis Interact more strongly with the orbitals of ligands

82. Criterion for d-d transition : - presence of unpaired d electrons in the d-block metal atoms or ions d-d transition is possible for 3d 1 to 3d 9 arrangements d-d transition is NOT possible for 3d and 3d 10 arrangements

83. 3d 9 : d-d transition is possible ↑↓↑↓↑ ↓ ↑↓↑ Cu 2+

84. 3d : d-d transition NOT possible Sc 3+

85. Potassium dichromate It is prepared in two steps : First the chromite ore ( FeCr 2 O 4 ) is fused with Na 2 CO 3 or K 2 CO 3 in free access of air 4 FeCr 2 O4 + 8 Na 2 CO 3 + 7O 2 8 Na 2 CrO 4 + 2 Fe 2 O 3 + 8 CO 2

86. STEP : 02 (ii) The yellow soln of sodium chromate is filtered and acidified with H 2 SO 4 to give a soln. from which orange sodium dichromate can be crystallized. 2 Na 2 CrO 4 + 2H + Na 2 Cr 2 O 7 +2Na + + H 2 O

87. Potassium dichromate to Sodium dichromate Sodium dichromate is more soluble than Potassium dichromate therefore K 2 Cr 2 O 7 is prepared by treating Na 2 Cr 2 O 7 with KCl. Na 2 Cr 2 O 7 + KCl K 2 Cr 2 O 7 + 2NaCl

88. Chromate and Dichromate ions CrO4 2- Cr O O O O 2- Chromate ion

89. Dichromate ion Cr 2 O 7 2- 2- O O O Cr O Cr O O O 126 179 pm 163 pm

90. Chemical properties K 2 Cr 2 O 7 and Na 2 Cr 2 O 7 are strong oxidising agents : In acidic solution its oxidising action can be represented as : Cr 2 O 7 2- +14H + +6e - 2Cr 3+ + 7 H 2 O (E =1.33V)