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The d- and f-Block Elements | 111
UNIT 7
THE d- AND f-BLOCK ELEMENTS
1. Introduction
d-block elements are present from fourth period onwards. There are mainly three
series of the transition metals – 3d series (Sc to Zn), 4d series (Y to Cd) and 5d series
(La to Hg, omitting Ce to Lu).
d-block elements are known as transition elements because their position in the
periodic table is between the s-block and p-block elements. Electronic configuration of
the d-block elements is (n – 1)d1-10nsº –2 but Cu+, Zn, Cd, Hg etc. [(n – 1)d10] are d-block
elements, but not transition metals because these have completely filled d-orbitals.
Transition Metals of d-block Elements
3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th
group group group group group group group group group group
ns2 d1 ns2d2 ns2d3 ns2d5 ns2d5 ns2d6 ns2d7 ns2d8 ns2d10 ns2d10
(n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1)
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os Ir Pt Au Hg
2. General Properties of the Transition Elements
(i) Atomic and Ionic Radii
In transition metals, left to right net nuclear charge increases due to poor
shielding effect. Due to this, the atomic and ionic radii for transition elements for a
given series show a decreasing trend for first five elements and then becomes almost
constant for next five elements of the series.
(ii) Enthalpies of Atomisation
Transition elements exhibit higher enthalpies of atomization because of large
number of unpaired electrons in their atoms. They have stronger interatomic interaction
and hence, stronger bond.
(iii) Ionisation Enthalpies
• In a series from left to right, ionization enthalpy increases due to increase in
nuclear charge.
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• The irregular trend in the first ionization enthalpy of the 3d metals, though
of little chemical significance, can be accounted for by considering that the removal of
one electron alters the relative energies of 4s and 3d orbitals.
(iv) Oxidation States
• Transition metals shows variable oxidation state due to two incomplete
outermost shells. Only stable oxidation states of the first row transition metals are
Sc(+ 3), Ti(+ 4), V(+ 5), Cr(+ 3, + 6), Mn(+ 2, + 7), Fe(+ 2, + 3), Co(+ 2, +
3), Ni(+ 2), Cu)+ 2), Zn(+ 2)
• The transition elements in their lower oxidation states (+ 2 and + 3) usually
forms ionic compounds. In higher oxidation state compounds are normally covalent.
• Only Os and Ru show + 8 oxidation states in their compounds.
• Ni and Fe in Ni(CO)4 and Fe(CO)5 show zero oxidation state.
(v) Trends in the Standard Electrode Potentials
• Transformation of the solid metal atoms to M2+ ions in solution and their
standard electrode potentials.
• If sum of the first and second ionization enthalpies is greater than hydration
enthalpy standard potential (EºM2+/M) will be positive and reactivity will be lower and
vice-versa.
(vi) Trends in Stability of Higher Oxidation States
The higher oxidation numbers are achieved in TiX4, VF5 and CrF6. The + 7 state
for Mn is not represented in simple halides but MnO3F is known and beyond Mn no
metal has a trihalide except FeX3 and CoF3 and increasing order of oxidizing power in
the series VO2+ < Cr2O72− < MnO4−.
(vii) Magnetic Properties
• When a magnetic field is applied to substances, mainly two types of
magnetic behavior are observed : diamagnetism and paramagnetism. Paramagnetism
due to presence of unpaired electrons, each such electron having a magnetic moment
associated with its spin angular momentum.
• The magnetic moment is determined by the number of unpaired electrons.
Magnetic moment = n ( n + 2)
where, n = number of unpaired electrons.
If all electrons are paired, substance will be diamagnetic and magnetic
moment will be zero.
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The d- and f-Block Elements | 113
(viii) Formation of Coloured Ions
• The d-orbitals are non-degenerated in presence of ligands. When an electron
from a lower energy d-orbital is excited to a higher energy d-orbital, the energy of
required wavelength is absorbed and rest light is transmitted out. Therefore, the colour
observed corresponds to the complementary colour of the light absorbed.
• In V2O5, V is in + 5 oxidation state. It is coloured due to defects in crystal
lattice.
(ix) Formation of Complex Compounds
• Transition metals have small size high nuclear charge which facilitates the
acceptance of lone pair of electron from ligands.
• They have vacant d-orbitals of appropriate energy in order to accommodate
the lone pair of electrons.
(x) Catalytic Properties
• Transition metals have two outermost shells incomplete and ability to adopt
multiple oxidation states and to form complexes, therefore used as a catalyst.
• Transition metals also provide larger surface area for the reactant to be
adsorbed.
(xi) Formation of Interstitial Compounds
• Small size of non-metals (H, C, N) fit into the voids of crystalline solid of
transition metals and form interstitial compounds.
• The principal physical and chemical characteristics of these compounds are
as follows :
(i) They have high melting points, higher than those of pure metals.
(ii) They are very hard, some borides approach diamond in hardness.
(iii) They retain metallic conductivity.
(iv) They are chemically inert.
(xii) Alloy Formation
Alloy is the homogeneous mixture of two or more metals. Transition metals have
approximate same size therefore, in molten form they can fit to each other crystalline
structure and form homogeneous mixture and form the alloy.
E.g., Brass (copper-zinc) and bronze (copper-tin) etc.
3. Some Important Compounds of Transition Elements
Potassium Dichromate (K2Cr2O7)
(i) Ore
Ferrochrome or chromate (FeO.Cr2O3) or (FeCr2O4)
The d- and f-Block Elements | 111
UNIT 7
THE d- AND f-BLOCK ELEMENTS
1. Introduction
d-block elements are present from fourth period onwards. There are mainly three
series of the transition metals – 3d series (Sc to Zn), 4d series (Y to Cd) and 5d series
(La to Hg, omitting Ce to Lu).
d-block elements are known as transition elements because their position in the
periodic table is between the s-block and p-block elements. Electronic configuration of
the d-block elements is (n – 1)d1-10nsº –2 but Cu+, Zn, Cd, Hg etc. [(n – 1)d10] are d-block
elements, but not transition metals because these have completely filled d-orbitals.
Transition Metals of d-block Elements
3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th
group group group group group group group group group group
ns2 d1 ns2d2 ns2d3 ns2d5 ns2d5 ns2d6 ns2d7 ns2d8 ns2d10 ns2d10
(n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1) (n – 1)
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os Ir Pt Au Hg
2. General Properties of the Transition Elements
(i) Atomic and Ionic Radii
In transition metals, left to right net nuclear charge increases due to poor
shielding effect. Due to this, the atomic and ionic radii for transition elements for a
given series show a decreasing trend for first five elements and then becomes almost
constant for next five elements of the series.
(ii) Enthalpies of Atomisation
Transition elements exhibit higher enthalpies of atomization because of large
number of unpaired electrons in their atoms. They have stronger interatomic interaction
and hence, stronger bond.
(iii) Ionisation Enthalpies
• In a series from left to right, ionization enthalpy increases due to increase in
nuclear charge.
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• The irregular trend in the first ionization enthalpy of the 3d metals, though
of little chemical significance, can be accounted for by considering that the removal of
one electron alters the relative energies of 4s and 3d orbitals.
(iv) Oxidation States
• Transition metals shows variable oxidation state due to two incomplete
outermost shells. Only stable oxidation states of the first row transition metals are
Sc(+ 3), Ti(+ 4), V(+ 5), Cr(+ 3, + 6), Mn(+ 2, + 7), Fe(+ 2, + 3), Co(+ 2, +
3), Ni(+ 2), Cu)+ 2), Zn(+ 2)
• The transition elements in their lower oxidation states (+ 2 and + 3) usually
forms ionic compounds. In higher oxidation state compounds are normally covalent.
• Only Os and Ru show + 8 oxidation states in their compounds.
• Ni and Fe in Ni(CO)4 and Fe(CO)5 show zero oxidation state.
(v) Trends in the Standard Electrode Potentials
• Transformation of the solid metal atoms to M2+ ions in solution and their
standard electrode potentials.
• If sum of the first and second ionization enthalpies is greater than hydration
enthalpy standard potential (EºM2+/M) will be positive and reactivity will be lower and
vice-versa.
(vi) Trends in Stability of Higher Oxidation States
The higher oxidation numbers are achieved in TiX4, VF5 and CrF6. The + 7 state
for Mn is not represented in simple halides but MnO3F is known and beyond Mn no
metal has a trihalide except FeX3 and CoF3 and increasing order of oxidizing power in
the series VO2+ < Cr2O72− < MnO4−.
(vii) Magnetic Properties
• When a magnetic field is applied to substances, mainly two types of
magnetic behavior are observed : diamagnetism and paramagnetism. Paramagnetism
due to presence of unpaired electrons, each such electron having a magnetic moment
associated with its spin angular momentum.
• The magnetic moment is determined by the number of unpaired electrons.
Magnetic moment = n ( n + 2)
where, n = number of unpaired electrons.
If all electrons are paired, substance will be diamagnetic and magnetic
moment will be zero.
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The d- and f-Block Elements | 113
(viii) Formation of Coloured Ions
• The d-orbitals are non-degenerated in presence of ligands. When an electron
from a lower energy d-orbital is excited to a higher energy d-orbital, the energy of
required wavelength is absorbed and rest light is transmitted out. Therefore, the colour
observed corresponds to the complementary colour of the light absorbed.
• In V2O5, V is in + 5 oxidation state. It is coloured due to defects in crystal
lattice.
(ix) Formation of Complex Compounds
• Transition metals have small size high nuclear charge which facilitates the
acceptance of lone pair of electron from ligands.
• They have vacant d-orbitals of appropriate energy in order to accommodate
the lone pair of electrons.
(x) Catalytic Properties
• Transition metals have two outermost shells incomplete and ability to adopt
multiple oxidation states and to form complexes, therefore used as a catalyst.
• Transition metals also provide larger surface area for the reactant to be
adsorbed.
(xi) Formation of Interstitial Compounds
• Small size of non-metals (H, C, N) fit into the voids of crystalline solid of
transition metals and form interstitial compounds.
• The principal physical and chemical characteristics of these compounds are
as follows :
(i) They have high melting points, higher than those of pure metals.
(ii) They are very hard, some borides approach diamond in hardness.
(iii) They retain metallic conductivity.
(iv) They are chemically inert.
(xii) Alloy Formation
Alloy is the homogeneous mixture of two or more metals. Transition metals have
approximate same size therefore, in molten form they can fit to each other crystalline
structure and form homogeneous mixture and form the alloy.
E.g., Brass (copper-zinc) and bronze (copper-tin) etc.
3. Some Important Compounds of Transition Elements
Potassium Dichromate (K2Cr2O7)
(i) Ore
Ferrochrome or chromate (FeO.Cr2O3) or (FeCr2O4)
