d – Block elements and Transition elements

d – Block elements:

The element in which electrons progressively enter in d – orbitals of its penultimate shell i.e. the (n – 1) d – orbital are called d – block elements. This block corresponds to groups 3 to 12 in the periodic table.

General valance electronic configuration of d – block elements is (n – 1) d 1-10 ns 1-2

Transition elements:

Those d – block elements have partially filled d – orbitals either in the elemental form or in their most common oxidation states.

d – Block elements are called transition elements. It is because, in the periodic table, they are placed in between s and p block elements and exhibit transitional behavior between highly reactive ionic compounds formed by s block elements on one side and covalent compounds formed by p block elements on the other side.

Sc = [Ar] 3d1 4s2

Ni = [Ar] 3d3 4s2

Cu ++ = [Ar] 3d  9

Partially filled d- orbitals are called transition metals.

However, elements of group 12 (Zn, Cd, and Hg) have completely filled d – orbitals in both elemental forms and in their most common oxidation state +2. Hence these elements are d – blocks but they are not considered a transition element. These elements are also called non-typical transition elements.

Zn = [Ar] 3d 10 4s2

Cd = [Kr] 4d 10 5s2

Hg = [Xe] 5d 10 6s2

Cn = [Rn] 6d 10 7s2

Also ,

Zn ++ = 3d 10

Cd++ = 4d 10

Hg ++ = 5d 10

They have completely filled d – orbitals so they are not typical transition metal.

General characteristics of transition elements:

  • They form complexes,
  • They have high melting and boiling point.
  • In most of the cations of the transition metals, they are unpaired electrons.
  • They have high density, malleability, ductility, possess metallic luster, good conductors of electricity ( except Zn, Cd, Hg, and Cn )
  • They form organometallic compounds like R2Cd , R2Zn, R2CuLi, etc.
  • They possess catalytic properties

Variable oxidation state | Valency

  • Transition elements exhibit 2 or more oxidation states i.e variable valency. This is due to the fact that the energy of (n-1)d and ns orbitals are almost the same and hence elements from both ns and (n-1) d orbitals are available for bonding.
  • The number of oxidation states exhibited by transition elements is directly proportional to the number of unpaired electrons present in atomic orbitals.


Sc = 3d1 4s2  ….. outer electronic configuration

Exhibit +2 oxidation state.

In those compounds in which it uses both of its 4s electrons.

It also exhibits +3 oxidation state

In this case, when it uses its two 4s electrons as well as one 3d electron in chemical bonding.

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