Transition Elements
The elements lying in the middle of the periodic table between group-2 and group-13 are known as
d-block elements. These d-block elements are called transition elements because they exhibit
transitional behaviour between s-block and p-block elements
Transition elements may be defined as the elements whose atoms or simple ions have partially filled
d-orbitals. Zinc, Cadmium and mercury are not considered as transition elements because their
atom as well as ion does not have partially filled orbitals
s-Block
p-Block
Transition elements (d -block)
Exhibit transitional behaviour Covalent - compound
between s - and p- blocks forming elements
Electronic Configuration
Depending upon the subshell ( 3d, 4d, 5d) involved, transition elements are mainly classified
into three series:
1. First transition series or 3d series : Elements of this series involves the filling of 3d orbitals.
2. Second transition series or 4d series : Elements of this series involves the filling of the 4d orbitals
3. Third transition series or 5d series : It consists of elements which involve the filling of 5d orbitals
There is also an incomplete fourth series starting with actinium.
General Electronic Configuration :
(n-1) d1-9 ns1-2
(n-1) stands for the penultimate shell and the d-orbital may have one to nine electrons and the s-orbital
of the ultimate shell (n) may two (or in some cases one) electrons.
Physicochemical Properties
1. Metallic Character :
, All the transition elements are metallic in nature and nearly all of them have
simple hcp, ccp or bcc lattices. Due to their greater effective nuclear charge and the large no. of
valence electrons, the metallic bond is quite strong and hence they are hard, possess high densities
and high enthalpies of atomisation.
2. Oxidation States :
Transition elements exhibit variable oxidation state due to the participation of ns as well as (n-1)d
electrons.
i) Except scandium, the most common oxidation state of the first row transition elements is +2
which arises from the loss of two 4s electrons, which means that after scandium, d-orbital
become more stable than the s-orbital.
ii) In the +2 and +3 oxidation states, bonds formed are generally ionic while in higher oxidation
states, the bond formed are essentially covalent. For example in MnO4- , CrO42- etc. the bonds
formed between metal and oxygen are covalent.
iii) The highest oxidation state shown by transition elements is +8.
3. Ionization Energy :
The ionization energies of transition elements are higher than those of s - block elements but lower
than p - block elements. In a particular transition series, ionization energy increases gradually as we
move from left to right, and it is due to the increase in nuclear charge.
It may be noted that the first ionization energies of 5d elements lie higher than those of 3d and 4d
elements because of the weak shielding of the nucleus by 4f electrons.
Further the magnitudes of ionization energies provide an indication of the energy needed to raise
the metal to a particular oxidation state in a compound. From the knowledge of values of ionization
energies of the metal it is possible to rationalize the relative stabilities of various oxidation state.
Ni(II) Compounds are thermodynamically more stable than Pt(II) compounds, on the other hand Pt
(IV) compounds are more stable than Ni (IV) compounds. It is due to that sum of first four ionization
energies is less for platinum whereas sum of the first two ionization energies is less for nickel. Hence
K2PtCl6 is a well known compound.
4. Complex formation (Complexation) :
Transition metal ions form variety of complexes due to the following reasons:
i) Small size and high nuclear charge.
ii) Availability of vacant d-orbitals of suitable energy, which can accept lone pair of electrons
donated by the molecule or ion (ligand).
5. Coloured Complexes :
Compounds of transition elements are usually coloured due to the promotion of an electron from
one d-orbital to another by the absorption of visible light. It can be clearly explained as follows:
The d-orbital in the transition elements do not have same energy in their complexes. Under the
influence of the ligand attached, the d-orbital split into two sets of orbital of slightly different
The elements lying in the middle of the periodic table between group-2 and group-13 are known as
d-block elements. These d-block elements are called transition elements because they exhibit
transitional behaviour between s-block and p-block elements
Transition elements may be defined as the elements whose atoms or simple ions have partially filled
d-orbitals. Zinc, Cadmium and mercury are not considered as transition elements because their
atom as well as ion does not have partially filled orbitals
s-Block
p-Block
Transition elements (d -block)
Exhibit transitional behaviour Covalent - compound
between s - and p- blocks forming elements
Electronic Configuration
Depending upon the subshell ( 3d, 4d, 5d) involved, transition elements are mainly classified
into three series:
1. First transition series or 3d series : Elements of this series involves the filling of 3d orbitals.
2. Second transition series or 4d series : Elements of this series involves the filling of the 4d orbitals
3. Third transition series or 5d series : It consists of elements which involve the filling of 5d orbitals
There is also an incomplete fourth series starting with actinium.
General Electronic Configuration :
(n-1) d1-9 ns1-2
(n-1) stands for the penultimate shell and the d-orbital may have one to nine electrons and the s-orbital
of the ultimate shell (n) may two (or in some cases one) electrons.
Physicochemical Properties
1. Metallic Character :
, All the transition elements are metallic in nature and nearly all of them have
simple hcp, ccp or bcc lattices. Due to their greater effective nuclear charge and the large no. of
valence electrons, the metallic bond is quite strong and hence they are hard, possess high densities
and high enthalpies of atomisation.
2. Oxidation States :
Transition elements exhibit variable oxidation state due to the participation of ns as well as (n-1)d
electrons.
i) Except scandium, the most common oxidation state of the first row transition elements is +2
which arises from the loss of two 4s electrons, which means that after scandium, d-orbital
become more stable than the s-orbital.
ii) In the +2 and +3 oxidation states, bonds formed are generally ionic while in higher oxidation
states, the bond formed are essentially covalent. For example in MnO4- , CrO42- etc. the bonds
formed between metal and oxygen are covalent.
iii) The highest oxidation state shown by transition elements is +8.
3. Ionization Energy :
The ionization energies of transition elements are higher than those of s - block elements but lower
than p - block elements. In a particular transition series, ionization energy increases gradually as we
move from left to right, and it is due to the increase in nuclear charge.
It may be noted that the first ionization energies of 5d elements lie higher than those of 3d and 4d
elements because of the weak shielding of the nucleus by 4f electrons.
Further the magnitudes of ionization energies provide an indication of the energy needed to raise
the metal to a particular oxidation state in a compound. From the knowledge of values of ionization
energies of the metal it is possible to rationalize the relative stabilities of various oxidation state.
Ni(II) Compounds are thermodynamically more stable than Pt(II) compounds, on the other hand Pt
(IV) compounds are more stable than Ni (IV) compounds. It is due to that sum of first four ionization
energies is less for platinum whereas sum of the first two ionization energies is less for nickel. Hence
K2PtCl6 is a well known compound.
4. Complex formation (Complexation) :
Transition metal ions form variety of complexes due to the following reasons:
i) Small size and high nuclear charge.
ii) Availability of vacant d-orbitals of suitable energy, which can accept lone pair of electrons
donated by the molecule or ion (ligand).
5. Coloured Complexes :
Compounds of transition elements are usually coloured due to the promotion of an electron from
one d-orbital to another by the absorption of visible light. It can be clearly explained as follows:
The d-orbital in the transition elements do not have same energy in their complexes. Under the
influence of the ligand attached, the d-orbital split into two sets of orbital of slightly different
