D Block Elements

The D-block elements are also known as the transition elements. The IUPAC defines these transition metals as an element whose atom has a particularly filled d subshell or which can give rise to citations with incomplete d subshells.

Transition metals are defined by the scientists as an element in the d-block of the periodic table. This includes group 3 to 12 on the periodic table. The F block lanthanide, actual and actinide series are also considered transition metals and are called inner transition metals.

Wilkinson and Cotton expanded the brief IUPAC definition by specifying which of the elements are included. The elements of group 4 to 11 and yttrium and scandium in group 3 which have partially filled d subshells in the metallic state. Actinium and lanthanum in group 3 are classified as lanthanides and actinides respectively.

Charles Bury, an English chemist, first used the word transition in this context in 1921 when he referred to a transition series of elements during the change in the inner layer of electrons from a stable group of 8 to one of 18 or from 18 to 32. 

These elements are known as the d block elements.


Classification

The atoms of elements have between one and ten d electrons in the d block:

4₂₁Sc₂₂Ti₂₃V₂₄Cr₂₅Mn₂₆Fe₂₇Co₂₈Ni₂₉Cu₃₀Zn5₃₉Y₄₀Zr₄₁Nb₄₂Mo₄₃Tc₄₄Ru₄₅Rh₄₆Pd₄₇Ag₄₈Cd6₅₇La₇₂Hf₇₃Ta₇₄W₇₅Re₇₆Os₇₇Ir₇₈Pt₇₉Au₈₀Hg7₈₉Ac₁₀₄Rf₁₀₅Db₁₀₆Sg₁₀₇Bh₁₀₈Hs₁₀₉Mt₁₁₀Ds₁₁₁Rg₁₁₂C.

The elements of group 11 to 4 are generally recognized as transition metals. The name justifies their typical chemistry that is a complex ion’s huge range in various oxidation state coloured complexes and catalytic properties either as the element or as ions. Y and SC in group3  are also generally recognised as the transition metals. The elements like La-Lu and Ac-Lr and group 12 attract different definitions from different authors. 

Few metals excluded from the list of transition metals are zinc, cadmium and mercury as they have electronic configuration of d10 and s2. 


Electronic Configuration

The electronic configuration of d block elements is (n-1)d1-10n s0-2. The period 7 and 6 transition metals also add (n-2)f0-14 electrons, which are omitted from the table below. 

The Madelung rule predicts that the typical transition metal atom electrons can be written as ns2(n-1)dm, where the inner d orbital is predicted to be filled after valence shells orbital is filled. The rule is approximated that it only holds for some of the transition elements and then in their neutral ground state.

The next to last subshell is the d subshell and is denoted as (n-1)d subshell. In the outermost subshell, the number of electrons is generally one or two except palladium, with no electron in that subshell in its ground state. In the valence shell, the s subshell is represented as the ns subshell. The transition metals in the periodic table are presented in the eighth group or in 3 or 12.


Properties

Transition metals share a number of properties elements that are not found in the other elements, which results from partially filled d shells. These include the following:

  • The compound whose colours are formed due to d-d electronic transition.

  • In many oxidation states, compound formation occurs due to the relatively low energy gap between different possible oxidation states.

  • The formation of many paramagnetic compounds due to the unpaired electron presence. Main group elements and few compounds are also paramagnetic.

  • Most of the transition metals can be bound to a variety of ligands allowing for a wide variety of transition metal complexes.

  • Coloured compounds: These compounds are generally due to the electronic configuration of  principal type:


Charge Transfer Transition: An electron may jump from a predominantly legendary orbit to a metal orbit. It gives rise to a ligand to metal charge transfer transition. Coloured compounds may generally occur when the metal is in a higher oxidation state. For example, the colour of dichromate and chromate and paramagnet ions due to the transition. 

A charge transfer from metal to ligand will be most likely when the metal is in the low oxidation state and the ligand is easily reduced.

Generally, the charge transfer ligand results in a more intense colour than the d-d transition.


Trends in Transition Metal Oxidation State

The ionization energies that are similar and relatively small increase in successive ionization energies lead to the formation of metal ions with the same charge of many transition metals. This, in turn, results in extensive horizontal similarities in chemistry which are most noticeable for the first-row transition metals and for the actinides and lanthanides. All the first row transitions except for Sc form stable compounds that have the 2+ ions. This is due to the small difference between the second and third ionization energy for all these elements except Zn from the stable compounds that contain 3+ ions. In successive ionization, the relatively small increase causes most of the transition metals to exhibit multiple oxidation states separated by a single electron.

For example, manganese forms compounds in every oxidation state between -3 and +7. Because of the steady but slow ionization potential across a row, higher oxidation state becomes progressively low or less stable for the elements on the right side of the d block. The multiple oxidation state occurrence which gets separated by a single electron causes many compounds of the transition metal to be paramagnetic with one to five unpaired electrons.

FAQ (Frequently Asked Questions)

Q1. Define the Common Oxidation State of D Block Elements?

Ans: The d block elements are also known as the transition metals. One of the two elements is scandium which is in the 1st transition metal period and which has only one oxidation state (zins is the other one with an oxidation state of +2). All the other elements which are present in the block have at least two different oxidation states.

Q2. Explain Why D Block Elements are Paramagnetic?

Ans: The d block elements are known as paramagnetic because unpaired electrons in (n-1)d orbitals are responsible for the magnetic properties. The character of paramagnetic of the transition metal increases on moving from left to right and as the number of unpaired electrons increases from one to five.

Q3. List Some Properties of the D Block Elements

Ans: There are many properties which they possess including Metallic nature, boiling and melting points, ionic radii, atomic densities and volume, ionizing potential, electronic configuration and oxidation state.

Q4. Why Do Block Elements Act as Good Catalysts?

Ans: The compounds of transition metals and itself the transition metal functions as a catalyst either because of their ability to change oxidation state or, in the case of the metals, to absorb other substances onto their surfaces and activate them in the process. All these are explored in the main catalyst section.