Representative or Main Group Elements

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These consist of all 's' and 'p' block elements excluding the noble gases (group 18 elements). The chemical properties of the representative elements are determined by the number of valence electrons in their atoms. The number of valence electrons belonging to the above two blocks are:

's' block elements: 1 or 2: Same as the group number

'p' block elements: 3 to 8: Group number minus ten

The representative elements are also known as normal or typical elements. Thus on the basis of their location in the periodic table, these are elements, which belong to groups 1, 2 and 13 to 17.

Noble gases or Aerogens

These consist of gaseous elements of group 18, the last group in 'p' block. All noble gases have a general outermost electronic configuration of 'ns' and 'np'. The only exception is helium having an outermost configuration of 1s². Because they display these stable characteristics (having completely filled outermost shells), they do not show any chemical reactivity. Only Xenon shows limited chemical reactivity under severe conditions.

Transition elements

'd' block elements are called transition elements. These elements occupy groups 3 to 12 on the periodic table. There are four series of transitional elements, '3d', '4d', '5d' and '6d' depending on the energy levels of 'd' orbitals. They have a general outermost electronic configuration of (n - 1) d^1-10 ns^1-2.

Inner transition elements

The 'f' block elements are called inner transition elements. There are two series of 'f' block elements. These are the '4f' and '5f' series called Lanthanides and Actinides. The general outer electronic configuration of 'f' block elements is, (n - 2) f^1-14 (n - 1) d^0-1 ns².

Problem

3. Discuss the position of inner transition elements in the periodic table.

Solution

The periodic table is unable to include the inner transition elements - lanthanides and actinides in its main frame. They have been allotted the same single place in the periodic table though their electronic configurations are not identical, because the variations in their properties is not much.