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f-Block: Lanthanoids - Electronic Configuration, Atomic And Ionic Size, Oxidation States

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f-Block: Lanthanoids - Electronic Configuration, Atomic And Ionic Size, Oxidation States - Lesson Summary

The 14 elements from Th to Lr in which the differentiating electron enters the 5f orbital, are called the actinoids.

Only the first three elements, namely thorium, protactinium and uranium, occur in nature.

All the actinoid elements are radioactive.


Electronic configuration:

5f1-14 6d0-1 7s2

The difference in energy between the 5f and 6d orbitals is small for the first four elements, thorium, protactinium, uranium and neptunium, the electrons in these elements and their ions may occupy the 5f or the 6d levels, or sometimes both.

Elements Symbol Electronic configuration  Thorium  Th  6d 2 7s 2  Protactinium  Pa  5f 2 6d 1 7s 2  Uranium  U  5f 3 6d 1 7s 2  Neptunium  Np  5f 4 6d 1 7s 2  Plutonium  Pu  5f 6 7s 2  Americium  Am  5f 7 7s 2  Curium  Cm  5f 7 6d 1 7s 2  Berkelium  Bk  5f 9 7s 2  Californium  Cf  5f 10 7s 2  Einstenium  Es  5f 11 7s 2  Fermium  Fm  5f 12 7s 2  Mendelevium  Md  5f 13 7s 2  Nobelium  No  5f 14 7s 2  Lawrencium  Lr   5f 14 6d 1 7s 2

Atomic and ionic radii:

The atomic and ionic radii of the tripositive and tetra positive actinoid ions there is a steady decrease in the ionic sizes of the tripositive and tetra positive ions. This may be referred to as actinoid contraction. Due to the poor shielding by the 5f electrons

Oxidation states:

Unlike lanthanoids, actinoids show a variety of oxidation states. This is attributed to the small energy difference between the 5f, 6d and 7s levels. +3 is the common oxidation state of actinoids.

The maximum oxidation state is +7.

EX: Neptunium and Plutonium.

Uranium exhibit +6 oxidation state.

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