Periodic Table: d-Block and f-Block Elements

Objectives of the Unit

• Learn the positions of d-block and f-block elements in the periodic table
• Understand the electronic configurations of transition (d-block) and inner transition (f-block) elements
• Appreciate the relative stability of various oxidation states in terms of electrode potential values
• Describe the preparation, properties, structures, and uses of important compounds like K2Cr2O7 and KMnO4
• Understand the general characteristics of d-block and f-block elements and their horizontal and group trends

The d-Block Elements

• The d-block elements are positioned in the middle section of the periodic table, flanked by s-block and p-block elements
• The d-block elements are divided into four series: 3d, 4d, 5d, and 6d
• The general electronic configuration of outer orbitals of d-block elements is (n-1)d ns, except for Pd
• The d-block elements exhibit characteristic properties like display of a variety of oxidation states, formation of colored ions, and entering into complex formation with ligands

The f-Block Elements

• The f-block elements are placed in a separate panel at the bottom of the periodic table
• The f-block elements are divided into two series: lanthanoids (4f) and actinoids (5f)
• The electronic configurations of f-block elements are similar to those of d-block elements

Position of the d-Block Elements in the Periodic Table

• The d-block elements occupy the large middle section of the periodic table
• The d-block elements are positioned between s-block and p-block elements

Electronic Configurations of the d-Block Elements

• The general electronic configuration of outer orbitals of d-block elements is (n-1)d ns, except for Pd
• The electronic configurations of d-block elements are given in Table 8.1

Characteristics of the Transition Elements

• The transition elements exhibit characteristic properties like display of a variety of oxidation states, formation of colored ions, and entering into complex formation with ligands
• The transition elements also exhibit catalytic property and paramagnetic behavior
• The transition elements have high enthalpies of atomization, which are shown in Fig. 8.2
• The transition elements have high melting points, which are shown in Fig. 8.1

Physical Properties of the Transition Elements

• The transition elements display typical metallic properties like high tensile strength, ductility, malleability, high thermal and electrical conductivity, and metallic lustre
• The lattice structures of transition metals are given in Table 8.2
• The transition elements have high melting points and boiling points, which are shown in Fig. 8.1
• The transition elements have high enthalpies of atomization, which are shown in Fig. 8.2### Lanthanoid Contraction
• Similar to ordinary transition series, lanthanoid contraction is attributed to imperfect shielding of one electron by another in the same set of orbitals.
• Shielding of one 4f electron by another is less than that of one d electron by another.
• As nuclear charge increases along the series, there is a regular decrease in the size of the entire 4f orbitals.

Atomic Radii and Density

• Atomic radii decrease across the series, resulting in an increase in density due to the increase in atomic mass.
• Significant increase in density is observed from titanium (Z = 22) to copper (Z = 29).

Electronic Configurations and Properties

• Table 8.2 lists the electronic configurations and some properties of the first series of transition elements.
• The table includes atomic number, electronic configuration, enthalpy of atomisation, ionisation enthalpy, metallic/ionic radii, and standard electrode potential.

Enthalpy of Atomisation

• Higher enthalpies of atomisation in transition elements are due to stronger interatomic interaction and bonding between atoms.
• Zinc has the lowest enthalpy of atomisation, 126 kJ mol-1.

Ionisation Enthalpies

• Ionisation enthalpies increase along each series of transition elements due to the increase in nuclear charge.
• Successive ionisation enthalpies do not increase as steeply as in non-transition elements.
• Irregular trend in the first ionisation enthalpy of the metals of the 3d series is attributed to the removal of one electron altering the relative energies of 4s and 3d orbitals.

Oxidation States

• Transition elements exhibit a great variety of oxidation states, with manganese exhibiting the most (from +2 to +7).
• The elements that exhibit the greatest number of oxidation states occur in or near the middle of the series.
• The lesser number of oxidation states at the extreme ends stems from either too few electrons to lose or share or too many d electrons.

Standard Electrode Potentials

• Table 8.4 contains the thermochemical parameters related to the transformation of solid metal atoms to M2+ ions in solution.
• The unique behaviour of Cu, with a positive E°, accounts for its inability to liberate H2 from acids.
• The general trend towards less negative E° values across the series is related to the general increase in the sum of the first and second ionisation enthalpies.### Element Properties
• The text provides a table showing the properties of elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, including their Δa H, Δi H, Δ1H2, Δ2H, ΔhydH, and E (M2+/M) values.

Trends in M3+/M2+ Standard Electrode Potentials

• The table shows varying trends in the E (M3+/M2+) values, reflecting the varying stability of the half-filled d sub-shell in Mn and the completely filled d configuration in Zn.
• The low value for Sc reflects the stability of Sc with a noble gas configuration.
• The highest value for Zn is due to the removal of an electron from the stable d configuration of Zn.

Trends in Higher Oxidation States

• Table 8.5 shows the stable halides of the 3d series of transition metals.
• The highest oxidation numbers are achieved in TiX4, VF5, and CrF6.
• The ability of fluorine to stabilise the highest oxidation state is due to either higher lattice energy or higher bond enthalpy terms for the higher covalent compounds.

Oxides of 3d Metals

• Table 8.6 shows the oxides of 3d metals, with the highest oxidation number coinciding with the group number and attained in Sc2O3 to Mn2O7.
• Oxygen has the ability to stabilise the highest oxidation state, exceeding that of fluorine.

Chemical Reactivity and E Values

• Transition metals vary widely in their chemical reactivity, with some being electropositive and dissolving in mineral acids, while others are "noble" and unaffected by single acids.
• The E values for M2+/M indicate a decreasing tendency to form divalent cations across the series.

Magnetic Properties

• The magnetic moment (μ) of an ion is calculated using the "spin-only" formula, μ = √n(n + 2), where n is the number of unpaired electrons.
• The magnetic moment increases with the increasing number of unpaired electrons.

Formation of Coloured Ions

• When an electron from a lower energy d orbital is excited to a higher energy d orbital, the energy of excitation corresponds to the frequency of light absorbed.
• The colour observed corresponds to the complementary colour of the light absorbed.
• The frequency of light absorbed is determined by the nature of the ligand, with water molecules as ligands in aqueous solutions.