Modern Periodic Table


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       The elements in which the last electron enters the f-orbitals of their atoms are called f-block elements. These consist of two series of elements placed at the bottom of the periodic table.

  1. Lanthanoids or Lanthanides or rare earth metals: The first series follows lanthanum, La (Z= 57) and the elements present in this series from cerium to lutetium (58Ce – 71Lu) are called lanthaniods or lanthanides. These are also called rare earth elements.

  2. Actinoids or Actinides: The second series follows actinium, Ac (Z = 89) and the elements present in this series from thorium to lawrencium (90Th - 103Lr) are called actionoids or actinides. These are of radioactive elements.

Periodic Table

The general electronic configuration of f-block elements may be written as: (n-2) f1-14 (n-1) d0-2 ns2 The elements included in these two series are called inner transition elements, because they form transition series within the transition elements of d-block.

6 General characteristics of f-block elements.

  1. They are heavy metals.

  2. They generally have high melting and boiling points.

  3. They exhibit variable oxidation states.

  4. They form coloured ions.

  5. They have the tendency to form complex compounds.

  6. Actinoids are radioactive in nature. The elements after uranium are called transuranium elements.

Test Your Understanding and Answer These Questions:

  1. What are lanthanoids or lanthanides?

  2. What are actinoids or actinides?

  3. Why are f block elements called inner transition elements?

  4. What is the general electronic configuration of f block elements?

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