d - and f -Block Elements

Inner Transition Elements

  • Elements of f-block (or) Inner transition elements {Group 3rd}:
    (i) Lanthanoids: Ce(58) to Lu(71). Only 61Pm is radioactive and synthetic element.
    (ii) Oxidation states: Common oxidation state is 3. Eu2+ (4f7), Yb2+ (4f14), Ce4+ (4f0) and Tb4+ (4f7) are quite stable
    (iii) Reducing properties: Ions with +2 oxidation state are reducing in nature.
    (iv) Oxidising properties: Ions with +4 oxidation state are oxidising in nature.
    (v) Paramagnetism: Most of metals and ions are paramagnetic due to the presence of unpaired electrons.
    (vi) Colour: (a) All metals are silvery white
                      (b) M3+ ions with 2 unpaired electrons have green shade.
  • Trick:
    (i) With 3 unpaired electrons have greenish pink or violet shade.
    (ii) With 4 and 5 unpaired electrons have yellow colour
    (iii) With 6 unpaired electrons have light pink colour.
    (iv) With 1 and 7 unpaired electrons have no colour
          Eg: Ce3+ and Yb3+
    (v) Ce4+ has no unpaired electron but has orange-red colour
    (vi) Yb2+ has no unpaired electron but has green colour.
  • Lanthanoid contraction: The contraction of size of Lanthanoids and trivalent ions with increase in atomic number is called lanthanoid contraction. This is due to increase in nuclear charge and dominatingly negligible screening (shielding) of 4f electrons by other electrons of the same subshell.
  • Consequences of Lanthanoid contraction:
    (a) Because of small difference in size of lanthanoids, their separation is possible by ion exchange method.
    (b) Basic strength of hydroxides is more for large cation.
           Ce(OH)3 > Lu(OH)3 ≥ La(OH)2 > La(OH)3 etc.
    (c) The properties of complex formation increases from La to Lu because of decrease in size and increase in "charge: Size" ratio is polarizing power
    (d) There is very slight increase in electronegativity from La to Lu
  • Uses of Lanthanoids:
    (1) Misch metal (Lanthanoids 94-95% & Fe 5% and traces of Al, Ca, S and C) is used for making steel for parts of jet engines.
    (2) Pyrophoric alloy (Ce 40.5 % La + Nd 4%, Fe 4.5 % Al 0.5% and traces of Si, Ca and C) is used for producing sparks.
    (3) La2O3 and Ce2O3 is used in sun glasses to cut heat and UV rays.
    (4) Oxides of lanthanoids are used for polishing glass.
  • Actinoids:
    (i) Th(90) to Lr(103), elements after U(92) are all synthetic.
    (ii) Most of the work was done by Seaborg. Because of less difference between energies of 5f and 6d oxidation states shown are +2 to +7. Oxo cations \tt UO_2^{2+},PuO_2^{2+} etc. are well known.
    (iii) Along the series atomic radius continuously decreases, though in many cases radii are not known because of radio active nature.
    (iv) Oxides and hydroxides are more basic than that of lanthanoids.
    (v) Ions having unpaired electrons are coloured (except f1 and f7) and are paramagnetic.

View the Topic in this Video from 0:40 to 1:01:11

Disclaimer: Compete.etutor.co may from time to time provide links to third party Internet sites under their respective fair use policy and it may from time to time provide materials from such third parties on this website. These third party sites and any third party materials are provided for viewers convenience and for non-commercial educational purpose only. Compete does not operate or control in any respect any information, products or services available on these third party sites. Compete.etutor.co makes no representations whatsoever concerning the content of these sites and the fact that compete.etutor.co has provided a link to such sites is NOT an endorsement, authorization, sponsorship, or affiliation by compete.etutor.co with respect to such sites, its services, the products displayed, its owners, or its providers.