The d- and f- Block Elements

Flashcards covering key vocabulary terms and concepts for the d- and f-block elements.

d-block elements

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

f-block elements

Elements in which 4f and 5f orbitals are progressively filled.

Transition metals

Often used to refer to the elements of d-block.

Inner transition metals

Often used to refer to the elements of f-blocks.

Four series of the transition metals

3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La and Hf to Hg) and 6d series which has Ac and elements from Rf to Cn.

Lanthanoids

4f (Ce to Lu)

Actinoids

5f (Th to Lr)

Transition metals (IUPAC Definition)

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

Group 12 Metals

Zinc, cadmium and mercury of group 12 have full d10 configuration in their ground state as well as in their common oxidation states and hence, are not regarded as transition metals.

Position of d-block in Periodic Table

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

Electron Reception in d-block

The d–orbitals of the penultimate energy level of atoms receive electrons giving rise to four rows of the transition metals, i.e., 3d, 4d, 5d and 6d series.

General Electronic Configuration of Transition Elements

Electronic configuration of outer orbitals of these elements is (n-1)d1–10ns1–2 except for Pd where its electronic configuration is 4d105s0.

Electronic Configuration of Zn, Cd, Hg, Cn

The orbitals in these elements are completely filled in the ground state as well as in their common oxidation states. Therefore, they are not regarded as transition elements.

Characteristic properties of Transition Elements

Display of a variety of oxidation states, formation of coloured ions and entering into complex formation with a variety of ligands.

Typical metallic properties of Transition Elements

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

Melting Points of Transition Metals

In any row the melting points of these metals rise to a maximum at d5 except for anomalous values of Mn and Tc and fall regularly as the atomic number increases.

Enthalpies of atomisation of transition elements

The maxima at about the middle of each series indicate that one unpaired electron per d orbital is particularly favourable for strong interatomic interaction. In general, greater the number of valence electrons, stronger is the resultant bonding.

Lanthanoid contraction

The filling of 4f before 5d orbital results in a regular decrease in atomic radii.

Factor responsible for the lanthanoid contraction

The imperfect shielding of one electron by another in the same set of orbitals.

Reason for higher enthalpies of atomisation in transition elements

Because of large number of unpaired electrons in their atoms they have stronger interatomic interaction and hence stronger bonding between atoms resulting in higher enthalpies of atomisation.

Terms responsible for the value of ionisation enthalpy

The three terms responsible for the value of ionisation enthalpy are attraction of each electron towards nucleus, repulsion between the electrons and the exchange energy.

Elements exhibiting the greatest number of oxidation states

Occur in or near the middle of the series.

Low Oxidation States

Low oxidation states are found when a complex compound has ligands capable of π-acceptor character in addition to the σ-bonding.

Low E° value for Sc

Reflects the stability of Sc3+ which has a noble gas configuration.

Highest E° value for Zn

Due to the removal of an electron from the stable d10 configuration of Zn2+.

Factors related to Eo values

The stability of the half-filled d sub-shell in Mn2+ and the completely filled d10 configuration in Zn2+ are related to their Eo values, whereas Eo for Ni is related to the highest negative ΔhydHo.

Unique behavior of Cu

Inability to liberate H2 from acids.

Fluorine stabilizing highest oxidation state

The ability of fluorine to stabilise the highest oxidation state is due to either higher lattice energy as in the case of CoF3, or higher bond enthalpy terms for the higher covalent compounds, e.g., VF5 and CrF6.

Oxygen stabilizing highest oxidation state

The ability of oxygen to stabilise the highest oxidation state is demonstrated in the oxides.

Reason for transition elements exhibiting higher enthalpies of atomisation

Because of large number of unpaired electrons in their atoms they have stronger interatomic interaction and hence stronger bonding between atoms resulting in higher enthalpies of atomisation.

Irregularity in Eo values

The Eo (M2+/M) values are not regular which can be explained from the irregular variation of ionisation enthalpies (ΔiH1 + ΔiH2 ) and also the sublimation enthalpies which are relatively much less for manganese and vanadium.

Ferromagnetic substances

Attracted very strongly are said to be ferromagnetic. In fact, ferromagnetism is an extreme form of paramagnetism.

Paramagnetism

Arises from the presence of unpaired electrons, each such electron having a magnetic moment associated with its spin angular momentum and orbital angular momentum.

Spin-only formula

n(n+2) where n is the number of unpaired electrons and µ is the magnetic moment in units of Bohr magneton (BM).

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 (Unit 5). This frequency generally lies in the visible region.

Complex compounds

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

Catalytic activity of Transition Metals

Their ability to adopt multiple oxidation states and to form complexes.

Interstitial compounds

Are those which are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals.

Interstitial compounds

Are not typically ionic nor covalent, for example, TiC, Mn4N, Fe3H, VH0.56 and TiH1.7, etc.

Principal physical and chemical characteristics of Interstitial compounds

High melting points, very hard, retain metallic conductivity and chemically inert.

Alloy

A blend of metals prepared by mixing the components.

Alloy

Homogeneous solid solutions in which the atoms of one metal are distributed randomly among the atoms of the other. Such alloys are 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, it is said to undergo disproportionation.

Oxides of metals

Are generally formed by the reaction of metals with oxygen at high temperatures.

Potassium dichromate use

Leather industry and as an oxidant for preparation of many azo compounds.

Potassium permanganate

Prepared by fusion of MnO2 with an alkali metal hydroxide and an oxidising agent like KNO3. This produces the dark green K2MnO4 which disproportionates in a neutral or acidic solution to give permanganate.

Uses of Potassium Permanganate

Besides its use in analytical chemistry, potassium permanganate is used as a favourite oxidant in preparative organic chemistry.

f-Block

Consists of the two series, lanthanoids (the fourteen elements following lanthanum) and actinoids (the fourteen elements following actinium).

Lanthanum in Lanthanoids

Because lanthanum closely resembles the lanthanoids, it is usually included in any discussion of the lanthanoids for which the general symbol Ln is often used.

Actinium in Actinoids

A discussion of the actinoids includes actinium besides the fourteen elements constituting the series.

Cerium

Shows a well-known +4 oxidation state in the series of lanthanoids.

Lanthanoid contraction

The overall decrease in atomic and ionic radii from lanthanum to lutetium. This contraction is, of course, similar to that observed in an ordinary transition series and is attributed to the same cause, the imperfect shielding of one electron by another in the same sub-shell.

Ce (IV)

Good analytical reagent

Pr, Nd, Tb, Dy

The +4 state but only in oxides, MO2

Pure metals of lanthanoids

Prepared from the oxides of the metals by reduction with calcium

Best single use of lanthanoids

Alloy steels for plates and pipes

Mischmetall

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

Catalysts in petroleum cracking

Mixed oxides of lanthanoids

Actinoids resemble Lanthanoids

4f orbitals and hence 5f electrons can participate in bonding to a far greater extent.

Actinoid contraction

Is greater from element to element in this series resulting from poor shielding by 5f electrons.