d - and f -Block Elements

Introduction and Properties of d-Block Elements

  • Elements of d-block:
    (1) This block has 40 elements, all metals and only 43Tc is radioactive
    (2) Electronic configuration (n − 1) d1 to 10 ns1 (or) 2
    (3) 3d series: Sc (Z = 21) to Zn (Z = 30)
         4d series: Y(Z = 39) to Cd (Z = 48)
         5d series: La (Z = 57) & Hf (Z = 72) to Hg (Z = 80)
         6d series: Ac (Z = 89) and Rf (Z = 104) to Cn (Z = 112)
  • Transition elements:
    (i) In ground state or stable oxidation state these have (n − 1) d1 to 9 ns1 (or) 2 electronic configuration.
    (ii) Zn, Cd, Hg and Cn are not considered as transition elements because in their ground state and stable oxidation state these do not have (n − 1) d1 to 9 electronic configuration, rather these have (n − 1) d10 system. Pd (Z = 40) has electronic configuration [Kr] 4d10 5s0.
  • Exceptional electronic configurations:
    (i) In 3d series Cr and Cu have exceptional electronic configurations 3d5 4s1 and 5d10 4s1 due to extra stability of the system. Cr and Mo have similar electronic configuration (n − 1) d5 ns1 for Mo, n = 5. Cu, Ag, and Au have similar electronic configuration (n − 1) d10 ns1 for Ag, n > 5 while for Au, n = 6
    (ii) Electronic configuration of 41Nb, 44Ru, 46Pd, 57La, 78Pt and 79Au also deviated from Aufbau principle. The assigned electronic configurations explain their properties.
    Eg: 46Pd has been assigned electronic configuration is [Kr] 4d10 instead of [Kr] 4d8 5s2 because in ground state Pd is diamagnetic.
  • Variable oxidation state:
    (i) Because of very small difference in energies of 3d- and 4s-subshells, elements of 3d series can use unpaired electrons of 3d-subshell along with 4s electrons to show variable oxidation states.
    Eg: (a) Cr (3d5 4s1) can show +2 to +6 oxidation states
          (b) Mn (3d5 4s2) can show +2 to 7 oxidation states.
    (ii) In aqueous solution Cr3+ is very stable due to 3d^{3}(t_{2g}^3) electronic configuration.
    (iii) Higher oxidation states are shown in oxides and fluorides. Zero oxidation state is shown in carbonyls.
    (iv) Os shows +8 oxidation state in OsO4
    (v) Oxides of d-block in +1, +2 and +3 oxidation states are basic except Mn2O3 and Cr2O3 which are amphoteric. Oxides in +4 oxidation states are amphoteric. Eg: MnO2
    (vi) Oxides in +5, +6 and +7 oxidation states are acidic
           Eg: V2O5, CrO3, and Mn2O7.
    (vii) Cu2+ is more stable than Cu+ because of lower E0 value.
           Cu2+/Cu = +0.34v, Cu+/Cu = + 0.52 v.
  • Atomic and Ionic radii:
    (i) Along the 3d series, the atomic radii decrease but becomes constant when pairing of electrons takes place in d-subshell. Size of Zn dominates because of high repulsion of paired electrons.
Element Sc Ti V Cr Mn Fe Co Ni Cu Zn
At.radius (pm) 164 147 135 129 127 126 125 125 128 138
  • (iii) Ionic radii continuously decreases
+2 ion Ti2+ V2+ Cr2+ Mn2+ Fe2+ Co2+ Ni2+ Cu2+
Radius (pm) 90 88 84 80 76 74 72 69
  • Ionization energy:
    (i) Along a series the I.E increases but not regularly. Cr(3d5 4s1) and Cu(3d10 4s1) show lower values of their 1st I.E but quite high for 2nd I.E
    (ii) Down a group I.E shows irregular trend of increase and decrease from 3d to 4d series, but 5d series elements have much higher I.E than 3d and 4d elements in their groups because of lanthanide contraction and high increase in nuclear charge.
    (iii) IE in kJ mole−1, down a group "↑" shows increases "↓" shows decrease of I.E.
Sc Ti V Cr Mn Fe Co Ni Cu Zn*
631 656 650 652 717 762 758 737 745 906
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd*
616 ↓ 674↑ 664↑ 685↑ 703↓ 711↓ 720↓ 804↑ 731↓ 876↓
La Hf Ta W Re Os Ir Pt Au Hg*
641↑ 760↑ 760↑ 770↑ 759↑ 840↑ 900↑ 870↑ 889↑ 1007↑
  • (iv) Zn, Cd, Hg and Cn are non-transition element having (n − 1) d10 ns2, completely filled subshells with all electrons paired up.
           IEMg > IEZn > IECd.
    (v) In first transition series Fe in 2nd transition series Pd and in 3rd transition series Ir have highest 1st ionization energies.
  • Colour:
    (i) Absorption of certain colour from visible spectrum (380 to 760 nm) causes the substance to gain complementary colour. eg. Absorption of green light makes it have a shade of red.
    (ii) A ligand can split 5 orbitals of d-subshell into t2g {dxy, dyz, dzx} and eg \left\{d_{x^{2}-y^{2}},d_z^2\right\}. Shift of efrom t2g to eg is called d-d transition and causes colour.
    (iii) The colour of the ion depends up on the size of the ion, number of unpaired electrons, difference of energy between t2g and eg and nature of ligand.
    (iv) [Cu(H2O)4]2+ is pale blue while [Cu(NH3)4]2+ is deep blue. Anhydrous CuSO4 is colourless. In the 1st case the energy absorbed corresponds to red colour while in 2nd case, it is the energy corresponding to orange colour which is absorbed.
    (v) CrO_4^{2-},Cr_{2}O_7^{2-},MnO_4^{-},MnO_4^{2-} etc, do not have unpaired electrons but are coloured due to charge transfer.
  • Trick: Colour wheel: A colour wheel to determine the complementary colour of a substance from the colour of light absorbed, complementary colours are shown on the opposite sides of the colour
  • If a substance absorbs red colour (720 nm), it appears green.

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