Third Transition Series (Lanthanum to Mercury)

Transition Elements

• Elements between the S-block and the P-block are called transition elements or d-block elements.
• They show transitional properties between s and p-block elements.
• They have partially filled d-orbitals, hence called d-block elements.

General Electronic Configuration

• The general electronic configuration of d-block elements is (n-1)d1-10ns1-2.

Classification of Transition Series

• D-block elements are classified into four transition series corresponding to the filling of 3d, 4d, 5d, and 6d orbitals.

First Transition Series (3d Series)

• It starts from scandium (atomic number 21) and includes 10 elements till zinc (atomic number 30).
• Electronic configurations of elements in this series are:
  • Scandium: [Ar] 3d1 4s2
  • Titanium: [Ar] 3d2 4s2
  • ... (all the way to zinc)

Second Transition Series (4d Series)

• It starts from yttrium (atomic number 39) and includes 10 elements till cadmium (atomic number 48).
• Electronic configurations of elements in this series are:
  • Yttrium: [Kr] 4d1 5s2
  • Zirconium: [Kr] 4d2 5s2
  • ... (all the way to cadmium)

Third Transition Series (5d Series)

• It starts from lanthanum (atomic number 57) and includes 9 elements till mercury (atomic number 80).
• Electronic configurations of elements in this series are:
  • Lanthanum: [Xe] 5d1 6s2
  • Hafnium: [Xe] 4f14 5d2 6s2
  • ... (all the way to mercury)

Fourth Transition Series (6d Series)

• It contains only 3 elements: actinium (atomic number 89), and two elements with atomic numbers 104 and 105.
• This series is incomplete.

Characteristics of Transition Metals

• Transition metals except Zn, Cd, and Hg exhibit several physical and chemical properties.
• They have variable oxidation states due to the participation of both ns and (n-1)d electrons in bonding.