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General Characteristics of Actinides

Chemical Bonding
The elements in which the 5f orbital is filled as the electrons are added are termed as the actinides. As in lanthanides, the anti-penultimate 5f orbital is filled successively by the addition of one electron at each step. Thus, lanthanides are termed the first inner transition series while actinides constitute the second inner transition series.

Actinide series are named after actinium, the very first element of the series. In this series, the first four elements actinium, thorium, protactinium and uranium occur in nature. The other elements are artificial and are made by the nuclear bombardment.

General characteristics of Actinides:
  • Electronic Configuration:

  • It is not sure whether the last electron enters the 5f orbital or the 6d orbital as both have the same energy. Hence, there are two views regarding the electronic configuration of actinides. According to Seaborg view, the 5f orbital is filled from thorium, while in Dawson view the 5f orbital is filled from uranium and are called uranides.

    The general electronic configuration of actinium is [Rn] 5f0-14 6d0-2 7s2 where Rn is the electronic configuration of the element Radium.

  • Oxidation States:

  • Unlike lanthanides which show the +3 oxidation states, actinides show a variety of oxidation states from +3 to +6. However, +3 and +4 are the principal oxidation states. The +3 oxidation state is the most stable in Ac and all the other elements of the series. The +4 oxidation state is the most stable in Th and Pu. +5 in Pa and Np and +6 is seen in U.

  • Ionic radius:

  • In actinides, the ionic radius decreases as we move down the series. This decrease in ionic radius is termed as actinide contraction. This effect is due to poor screening offered by f electrons.

  • Complex formation:

  • Unlike lanthanides, they have the tendency to form complexes. Complex formation with ligands such as thio-ethers is also seen.

Solved problems
  • In actinides, the differentiating electron enters into the

    • 5f
    • 4f
    • 3d
    • 6f
    Answer: a
  • With the increase in atomic number, the ionic radius of actinides

    • Increases
    • Decreases
    • Unaffected
    • Depends on the presence of other elements.
    Answer: b
  • An oxidation that is seen in both actinides and lanthanides and is very stable is

    • +3
    • +4
    • +5
    • +6
    Answer: a
  • The chemistry of all the actinides is same because

    • Because the differentiating electron enters the 5f orbital in all the elements
    • Because they have same ionic radius
    • Because they have the same atomic radius
    • None
    Answer: a

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