What is d-Block Elements?

According to the modern form of periodic table, 118 elements are present which are subdivided as four blocks, namely, s, p, d and f-block elements based on the entry of the valence electron or last electron into which orbital.

The elements in the d-block of the periodic table receive the last or valence electron in the d-orbital. These elements containing partially filled d-subshell in their ground state configuration are termed as d-block elements. The groups from IIIB to VIIIB and IB to IIB comprise the d-block elements. They begin from the 4^th period in four series i.e. 3d, 4d, 5d and 6d of the modern periodic table. There are 10 elements in each series. The first transition series (3d series) starts with Sc-21 and ends with Zn-30, second transition series (4d) from Y-39 to Cd-48,the third transition series or 5d series La-58, Hf-72 to Hg-60 and the last series (6d) starts from Ac-89, Rf-104 to Cn-112.

All the 6d series are radioactive metals which do not occur in nature. They all are artificially synthesized in the laboratory. The elements between La-58 to Hf-72 in 5d series are lanthanides and Ac-89 to Rf-104 in 6d series are actinides included under f-block elements.

Position of the Elements of d-block in Periodic Table 

In the periodic table, the elements of d-block are placed between the elements of s-block and p-block. These elements of d-block are also termed as transition elements. Most of the properties of the elements of d-block show gradual transition linking the properties of the elements of s-block (highly reactive electropositive) and the p-block (electronegative). Thus the d-block elements act as the transition state of the properties of both the elements of s to p-block. Thus these elements are also given the name as transition elements.

The 2B group elements i.e. Zn, Cd, Hg, Cn contain completely filled d-orbitals in the ground state and also in the stable oxidation state. But the valence electron enters in to the d- or penultimate shell. Thus these elements are considered as the elements belonging to d-block but are not transition elements. Thus it is said as “All transition elements are the elements of d-block but all the elements in d-block are not transition elements”. 

Electronic Configuration of the Elements of d-Block

The general valence shell electronic configuration of the elements of d-block is (n-1)d^1-10ns^1-2. Here (n-1) is the penultimate shell in which the d-orbital contains 1 to 10 electrons and n is the outermost shell in which the s-orbital contains 1 or 2 electrons. In general, the electrons are filled up based on Aufbau and Hund’s rule along the period.

The partially filled and completely filled orbitals of d are considered stable and thus to gain the stability, the s-electron is taken up with the d-orbital. This is also based on the pairing energy of s-electrons. This abnormal behavior is observed in case of chromium and copper in 3d series as shown in the table. A similar trend in observed in case of 4d, 5d and 6d series.

General Properties for the Elements of d-Block

Oxidation states

All the d-block elements are known to show various oxidation states except the first and last element of each series. This is because of the involvement of both ns and (n–1)d electrons in bonding. The general +2 oxidation state is due to s-electron, while the higher oxidation states (+3 to +7) are because of the loss of both s-and d-electrons. The s-electron or the lower oxidation state of d-block elements lead to ionic bonding, whereas higher oxidation state due to d-electrons lead to covalent bond formation. Manganese shows highest number of oxidation states (+2 to +7) and the highest oxidation state of the transition metals is +8 exhibited by ruthenium and osmium.

Metallic nature

All the transition elements are metallic in nature. They have the qualities of metals such as high tensile strength, malleability and ductility, and readily form alloys with different metals. They conduct heat and electricity fabulously indicating the existences of metallic bond within the metals. All the transition metals are hard and fragile in nature except mercury which is a fluid. The hard and fragile nature of transition metals indicates the presence of covalent bonding. Due to this covalent bonding nature, except Zn, Cd and Hg, all the metals exhibit elevated melting and boiling points.

Atomic and ionic radii

In general atomic radius decreases along the period and increases along the group. Transition metals show a peculiar behavior in the atomic radius trend. For instance, in 3d series, the atomic radius decreases drastically from Sc till Cr, further remains same from Mn to Ni followed by gradual increase for Cu and Zn. As the quantity of d-electrons increases, the effective nuclear charge and the shielding effect also increases. Thus, from Sc to Cr, the shielding effect is poor due to less number of d-electrons but due to high effective nuclear charge leads to drastic increase in size. From Mn to Ni, the effective nuclear charge is balanced by the shielding effect leading to no change in the size. In Cu and Zn, the d-orbitals are fully filled which shields the outer shell s-electron leading to increase in the atomic size than its previous elements.

Similarly, the increase in atomic size is seen from 3d to 4d elements but the radii of 4d and 5d series are almost same because of an effect named lanthanide contraction. In 5d series, after lanthanum, the electron enters the 4f subshell and then the 5d orbital is filled up. Due to this the effective nuclear charge increases leading to the decrease in size or compensating the increase in size. As a contraction is taking place, it is named as lanthanide contraction. Thus, the atomic or ionic radii trend for the elements of d-block varies unexpectedly.

Ionization Potential or Ionization energy

The minimum quantity of energy required for removing an electron from the valence shell of an atom or ion is called ionization energy. Hence ionization energy is directly related to nuclear charge and inversely related to atomic radii. In d-block elements, from left to right as the atomic size decrease, increase in the first ionization energy is noticed except in case of partially filled and fully filled d-orbitals, where those metals require less energy for removing the s-electron. But the second ionization energy of these d-block elements will be much higher, as it involves removal of electron from a stable configuration.

Magnetic Properties

Magnetic property of an element is depicted based on the number of unpaired electrons in it. The d-block elements exhibit paramagnetic and diamagnetic. Paramagnetic property is shown by the substances which get pulled in by the magnetic field as they contain unpaired electrons. Diamagnetic property is shown by the substances which repel the magnetic field and contain paired electrons. Few metals such as iron, cobalt and nickel exhibit spontaneous net magnetic behavior even in the non-appearance of magnetic field. These are called ferromagnetic compounds.

Colored compounds

Most of the d-block elements form colored compound with the organic ligands either in solid or liquid states. In presence of ligands, the degeneracy of the d-orbitals are lost and split into two sets, namely e_g and t_2g set. When light gets incident on a transition metal, the electron in the lower energy t_2g set gets excited to the higher energy e_g set by absorbing certain radiations. The transmitted light is the color of the compound which will be the complementary color of the absorbed light.

Context and Applications   

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for   

• Bachelor of Chemistry       
• Master of Chemistry

Practice Problems

1. In 3d series, anomalous electronic configuration is shown by 

a. Sc and Zn           b. Cr and Mn           c. Cr and Cu            d. Fe and Ni  

Solution: c. Cr and Cu

          Cr: 24 – 1s²2s²2p⁶3s²3d⁵4s¹  and  Cu – 29 1s²2s²2p⁶3s²3d¹⁰4s¹  

2. Find out the elements which are considered as d-bloc elements but not transition elements?

a. Cu, Ni, Fe            b. Fe, Os, La           c. Zn, Tc, Ce           d. Zn, Cd, Hg 

Solution: d. Zn, Cd and Hg are elements of d-block but not transition elements due to the full filled d-orbitals.