The d- and f- Block Elements

Flashcards for reviewing key concepts related to d-block and f-block elements from the lecture notes.

d-block

Elements of the groups 3-12 in which the d orbitals are progressively filled in each of the four long periods.

f-block

Elements in which 4f and 5f orbitals are progressively filled, placed at the bottom of the periodic table.

Transition metals and inner transition metals

Elements of d- and f-blocks, respectively.

Transition metal series

Four series: 3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La and Hf to Hg) and 6d series (Ac and Rf to Cn).

Inner transition metal series

Two series: 4f (Ce to Lu) and 5f (Th to Lr).

Transition Metals (IUPAC definition)

Metals which have incomplete d subshell either in neutral atom or in their ions.

Zinc, Cadmium, Mercury

Elements with (n-1)d10 ns2 configuration, not regarded as transition metals.

Position of d-block in the Periodic Table

The d–block occupies the large middle section of the periodic table flanked between s– and p– blocks.

Electronic Configuration of d-block elements

Outer orbitals electronic configuration (n-1)d1-10 ns1-2 (with exceptions like Pd).

Scandium (Sc)

Atomic number 21, is a transition element because of incompletely filled 3d orbitals (3d1).

Zinc (Zn)

Atomic number 30, is not a transition element because of completely filled d orbitals (3d10).

Metallic properties of transition elements

High tensile strength, ductility, malleability, high thermal and electrical conductivity, and metallic luster.

Exceptions in metallic structure

Zn, Cd, Hg, and Mn have structures that deviate from typical metallic structures at normal temperatures.

High melting points of transition metals

Attributed to involvement of greater number of electrons from (n-1)d in addition to ns electrons in interatomic metallic bonding.

Enthalpies of atomisation trend

Metals of the second and third series have greater enthalpies of atomisation than the corresponding elements of the first series.

Decrease in ionic radius

The imperfect shielding effect of d electrons causes the net electrostatic attraction between the nuclear charge and outermost electron to increase, thus ionic radius decreases.

Lanthanoid Contraction

Filling of 4f orbitals before 5d leads to similar radii between 4d and 5d series elements.

Cause of Lanthanoid Contraction

The imperfect shielding of one 4f electron by another.

High enthalpies of atomisation

Because of large number of unpaired electrons in their atoms they have stronger interatomic interaction resulting in stronger bonding between atoms.

Factors affecting ionization enthalpy

Attraction of each electron towards the nucleus, repulsion between the electrons, and exchange energy.

Exchange energy

Responsible for the stabilisation of energy state and is approximately proportional to the total number of possible pairs of parallel spins in the degenerate orbitals.

Variety of oxidation states

Arises out of incomplete filling of d orbitals, such that oxidation states differ by unity.

Group 6 oxidation states

Mo(VI) and W(VI) are more stable than Cr(VI).

Low oxidation states

Requires ligands capable of π-acceptor character in addition to the σ-bonding.

Transition element without variable oxidation states

Scandium does not exhibit variable oxidation states.

General trend in M2+/M standard electrode potentials (E°)

Related to the general increase in the sum of the first and second ionisation enthalpies.

Factors related to E° values of Mn and Zn

Stability of half-filled d sub-shell in Mn2+ and completely filled d10 configuration in Zn2+.

Ability of fluorine to stabilise higher oxidation states

Due to either higher lattice energy or higher bond enthalpy terms for higher covalent compounds.

Chemical reactivity

Transition metals vary widely in their chemical reactivity; many dissolve in mineral acids, while some are noble.

Irregular Eo (M2+/M) values

The observed E°(M2+/M) values are not regular due to irregular variation of ionisation enthalpies and sublimation enthalpies.

Paramagnetism

Paramagnetism arises from the presence of unpaired electrons.

Significance of magnetic moment

Observed magnetic moment gives a useful indication about the number of unpaired electrons.

Formation of colored ions

When an electron from a lower energy d orbital is excited to a higher energy d orbital.

Complex compounds

Those in which the metal ions bind a number of anions or neutral molecules, giving complex species with characteristic properties.

Catalytic Activity

Ability to adopt multiple oxidation states and to form complexes.

Interstitial compounds

Formed when small atoms are trapped inside the crystal lattices of metals, usually non-stoichiometric.

Alloy

Blend of metals prepared by mixing the components. Formed by atoms with metallic radii that are within about 15 percent of each other.

Disproportionation

When a particular oxidation state becomes less stable relative to other oxidation states, one lower, one higher.

Formation of oxides

These oxides are generally formed by the reaction of metals with oxygen at high temperatures.

Mischmetall

The alloy consists of a lanthanoid metal (~95%) and iron (~5%) and traces of S, C, Ca, and Al.

Actinoids

The f-block elements from Th to Lr.

Irregularities in electronic configurations of actinoids

Related to the stabilities of the f0, f7, and f14 occupancies of the 5f orbitals.

Actinoid contraction

The general trend in lanthanoids is observable in the actinoids as well.

Oxidation states of actinoids

+3 oxidation state is dominant, with early members exhibiting higher oxidation states.