Transition Metals: Class 12 Inorganic Chemistry Notes

Unit 6. Transition metals

Three series of elements formed by filling the 3d, 4d, and 5d shells of electrons are called d-block elements.

The electronic configuration of d-block elements are generally represented
by (n-1)d^1-10 ns^1-2 . Where (n-1) is penultimate shell.

In s-block and p-block element, the outermost orbital is filled. But in the d-block element electrons are added to the penultimate shell.

They are often called ‘transition elements’ because their position in the periodic table is between the s-block element( which formed ionic compound ) and the p-block element( which are largely covalent ).

Transition series

• There are three complete rows of ten elements and one incomplete row in d-block of periodic table.
• These rows are called first, second, third, and fourth transition series which involves filling of 3d, 4d, 5d, and 6d orbitals respectively.
• These series are also called transition series.
  

1. First transition series: It contains ten elements from Scandium(At. No. 21) to Zinc (At. No. 30). They have incomplete 3d-orbitals.
2. Second transition series: It contains ten elements from Yttrium (At. No. 39) to Cadmium(At. No. 48). They have incomplete 4d-orbitals.
3. Third transition series: It contains ten elements with incomplete 5d�-orbitals and constitute elements Lanthanum (At. No. 57) and from Hafnium (At. No. 72) to Mercury(At. No. 80).
4. Fourth transition series: It has incompletely filled f-group elements. This consist of Lanthanide and actinides.