The d-and f-Block Elements | Unit 8 | Chemistry

D-block or transition elements

These are the elements that are located in the middle of the Periodic Table between s-block and p-block elements, or between group 2 and 13.

The d and f block Elements

There are three series of transitions, each with ten elements
  • The first transition series concerns the filling of three-dimensional orbitals. Beginning with scandium (Z = 21), it progresses to zinc (Z = 30).
  • The second sequence of transitions entails the filling of 4d-orbitals. It begins with yttrium (Z=39) and ends with cadmium (Z=48).
  • Third transition series : 5d-orbitals are filled in this series. This series’ first element is lanthanum (Z = 57). It is followed by 14 lanthanides, which are composed by filling 4f-orbitals. From hafnium (Z = 72) to mercury (Z = 80), the following nine elements are third-class.

The components of the f-block are known as inner-transition components.

All transitional elements are metallic in nature, excellent heat- and electricity-conductors, and exhibit a steady decrease in electropositive character over time. These metals are hard, have high densities, high enthalpies of atomization, high melting and boiling temperatures, and form alloys with other metals because of their strong metallic connections.

Towards the conclusion of the sequence
  •  The melting point of these first materials reaches its maximum and then gradually declines.
  •  The quantity of partially filled d-orbitals is closely correlated with the strength of metallic connections.
  • As the atomic number increases, the radii of ions in a given series that have the same charge and magnitude gradually shrink. Due of the inadequate shielding effect of.
Ionisation energy
  • Transition elements have lower ionisation energies than p-block elements 
  • But greater ionisation energies than s-block elements. In the series, it often gets bigger from left to right.
  • Different oxidation states can be seen in transition metals.
Oxidation state of different metal

The participation of ns and (n – 1)d- electrons in bonding is the cause of the varied oxidation states of transition metals.

The majority of transition metals have enough electropositivity. H2 gas is released when they interact with mineral acids.

Many of the compounds of transition elements exhibit paramagnetic behaviour.

Another property of transition metals that is frequently seen is the formation of coloured compounds, both in the solid state and in aqueous solutions. This is caused by the absorption of some radiation from visible light, which leads to the electron d-d transition.

The transition elements can form complexes, in contrast to the s- and p-block components. This is due to the fact that

  • these elements have tiny, highly charged ions, and
  • have empty d-orbitals.

In numerous processes, transition metals and their compounds serve as catalysts.

A lot of interstitial compounds are formed by transition metals.

Transition metals are used to create a variety of alloys. It is because the atoms in their metal crystal lattices can easily swap places with one another.

Transition metal oxides tend to have basic or acidic natures in lower oxidation states and amphoteric or basic natures in higher oxidation states.

According on whether the last electron (differentiating electron) enters 4f or 5f orbitals, the f-block elements have been separated into two series and are referred to as lanthanides or actinides, respectively.

  • Actinides exhibit a variety of oxidation states, however the most prevalent one is + 3. Actinides exhibit the maximum oxidation state at + 7.
Lanthanide properties

 The electrical configuration of lanthanides is generally

  • [Xe] 4f1-14 5d0-1 6s2.

The colours of the metals are silvery-white. They have low tensile strength, are ductile, malleable, and excellent thermal and electrical conductivity.

They have high melting points and a reasonably high density.

The main oxidation state of the lanthanides is + 3. Some substances do, however, also have + 2 (Eu2+) and + 4 (Ce4+) oxidation states.

The electronic transition between the various 4 f-levels gives rise to the coloured nature of many lanthanide ions.

The unpaired electrons in the majority of the lanthanide ions cause paramagnetism. La3+ and Ce4+ are two examples of lanthanoid ions that do not exhibit paramagnetism, as are Yb2+ and Lu3+, which both have a completed 4f-level.

Trioxides are produced when the lanthanides tarnish easily in air and on surfaces (except cesium, which forms Ce02).

The lanthanide oxides and hydroxides have a basic nature.

Ionic compounds make up the majority of lanthanoid compounds.

READ MORE: Chemistry Class 12 Chapter 7 – The p-Block Elements

Lanthanoid contraction

It refers to this gradual reduction in atomic size throughout the first f- transition element series.

The general electronic configuration of actinides is:-

  • [Rn] 5f0-14 6ds0-1 7s2.

All of the elements are metallic and silvery-white.

The actinides have somewhat high melting points.

The actinides’ ionic size rapidly diminishes over the sequence.

The actinides are capable of displaying a variety of oxidation states. In actinides, +4 oxidation state is preferable.

Some actinoid elements, such as uranium, neptunium, and plutonium, can exist in the +6 oxidation state.

A lot of the actinoid components contain radioactivity. The elements created by humans come after uranium.

Compared to lanthanides, the actinides have a far stronger propensity to form complexes.

Some important compound of transition elements:

a. Metal oxydes and oxyanions

b. In most cases, metals and oxygen react at high temperatures to generate oxides.

c. The following are some significant transition element compounds:

Dichromate of potassium,( K2Cr2O7)

a. It is employed in the production of several azo compounds as well as the leather industry.

b. With sodium carbonate, the following reaction takes place:

FeCr2O4+8Na2CO3+7O2 → 8Na2CrO4 + 2Fe2O3 + 8CO2

Potassium permanganate(KMnO4)

K2MnO4 is produced when KOH and finely powdered MnO2 are fused.

2MnO2 + 4KOH + O22K2MnO4 + 2H2O

MnO2 is first fused alkaline oxidatively and then electrolytically with oxygen to create it.

​The Actinides

Actinoids are the 14 elements with atomic numbers 90 (Thorium) through 103 (Lawrencium) that follow actinium (89). The second inner transition series includes them.

These elements’ names, symbols, and electrical configurations are provided:

Elements Symbol Outer Electronic
Oxidation states
89 Actinium Ac [Rn]  5F06D17S2 III
90 Thorium Th [Rn]  5F06D27S2 III  IV
91 Protactinium Pa [Rn]  5F26D17S2 III  IV  V
92 Uranium U [Rn]  5F36D17S2 III  IV  V  VI
93 Neptunium Np [Rn]  5F46D17S2 III IV  V  VI  VII
94 Plutonium Pu [Rn]  5F66D07S2 III  IV  V  VI  VII
95 Americium Am [Rn]  5F76D07S2 III  IV  V  VI
96 Curium Cm [Rn]  5F76D17S2 III  IV
97 Berkelium Bk [Rn]  5F96D07S2 III  IV
98 Californium Cf [Rn]  5F106D07S2 II  III
99 Einsteinium Es [Rn]  5F116D07S2 II  III
100 Fermium Fm [Rn]  5F126D07S2 II  III
101 Mendelevium Md [Rn]  5F136D07S2 II  III
102 Nobelium No [Rn]  5F146D07S2 II  III
103 Lawrencium Lr [Rn]  5F146D17S2 III
104 Rutherformium Rf [Rn]  5F146D27S2

Radioactive substances make up the actinoids. For lawrencium (Z =103), the half-life values range from a day to 3 minutes.

Oxidation state

Actinoids mostly exist in the +3 oxidation state. However, because the energies of the 5f, 6d, and 7s subshells are similar, they too exhibit varying oxidation states. For instance, uranium exhibits the oxidation states of and. Neptunium (Z = 93) has oxidation states of up to +7.

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