Coupon Accepted Successfully!



d- and f-block elements are often called “transition elements” because their position in the periodic table is between the s-block and p-block elements. Their properties are transitional between the highly reactive metallic elements of the s-block, which typically forms ionic compounds, and the elements of the p-block, which are largely covalent. Typically the transition elements have an incompletely filled d-level. Group 12 (the zinc group) has a d10 configuration since the d-subshell is complete. Compounds of these elements are not typical and show some differences from the others.
Thus, the transition elements are defined as those elements which have partly filled d-orbitals, as elements and in any of their important compounds.
The general electronic configuration of the d-block elements can be represented as:
(n – 1)d1 – 9 ns1–2
Unlike the s- and p-block elements of the same period, the d-block elements do not show much variation in properties, both chemical and physical. This is because these elements differ only in the number of electrons in the penultimate d-shell. The number of electrons in the valence shell remains the same, ns2, for most of the elements.

Metallic character

All the transition elements are metals. They are good conductors of heat and electricity, have a metallic luster and are hard, strong, and ductile. They also form alloys with other metals. Copper exceptionally is both soft and ductile and relatively noble.

Variable oxidation states

One of the most striking features of the transition elements is that the elements usually exist in several different oxidation states, and the oxidation states change in units of one.
For example, Fe3+ and Fe2+, Cu2+ and Cu+, etc.
The oxidation states shown by the transition elements may be related to their electronic configurations. Calcium, the s-block element preceding the first row of transition elements, has the electronic configuration:
Ca (Z = 20): 1s22s22p63s23p64s2: [Ar]4s2
The oxidation states of the d-block elements are listed as follows:

Once the d5 configuration is exceeded, i.e., in the last five elements, the tendency for all the d-electrons to participate in bonding decreases. Thus, Fe has a maximum oxidation state of (VI). However, the second and third elements in this group attain a maximum oxidation state of (VIII), as in RuO4 and OsO4. This difference between Fe and the other two elements (Ru and Os) is attributed to the increased size and decreased attraction with the nucleus.
The oxidation number of all elements in the elemental state is zero. In addition, several of the elements have zero-valent and other low-valent states in complexes. Low oxidation states occur particularly with Ti-bonding ligands such as carbon monoxide and dipyridyl.

Atomic and ionic radii

The covalent radii of the elements decrease from left to right across a row in the transition series, until near the end when the size increases slightly. On passing from left to right, extra protons are placed in the nucleus and extra orbital electrons are added. The orbital electrons shield the nuclear charge incompletely (d-electrons shield less efficiently than p-electrons, which in turn shield less effectively than s-electrons). Because of this poor screening by d-electrons, the nuclear charge attracts all of the electrons more strongly, and hence a contraction in size occurs.
The elements in the first group in the d-block (group 3) show the expected increase in size Sc Y La. However, in the subsequent groups (4–12), there is an increase in radius of 0.1 0.2 Å between the first and second members, but hardly any increase between the second and third elements. This trend is shown both in the covalent radii and ionic radii. Interposed between lanthanum and hafnium are the 14 lanthanide elements, in which the anti-penultimate 4f-subshell of electrons is fitted.
There is a gradual decrease in size of the 14 lanthanide elements from cerium to lutetium. This is called the “lanthanide contraction.” The lanthanide contraction cancels almost exactly the normal size increase on descending a group of transition elements. Therefore, the second and third row transition elements have similar radii. As a result they also have similar lattice energies, solvation energies, and ionization energies. Thus, the differences in properties between the first row and second row elements are much greater than the differences between the second and third row elements. The effects of the lanthanide contraction are less pronounced towards the right of the d-block. However, the effect still shows to a lesser degree in the p-block elements that follow.


The atomic volumes of the transition elements are low compared with elements in neighboring groups 1 and 2. This is because the increased nuclear charge is poorly screened and so attracts all the electrons more strongly. In addition, the extra electrons added occupy inner orbitals. Consequently, the densities of the transition metals are high.

Melting and boiling points

The melting and boiling points of the transition elements are generally very high. Transition elements typically melt above 1000°C.

Ionization energy

In a period, the first ionization energy gradually increases from left to right. This is mainly due to increase in nuclear charge. Generally, the ionization energies of transition elements are intermediate between those of s- and p-block elements. The first ionization potential of the 5d-etements are higher than those of 3d and 4d-elements due to the poor shielding by 4f-electrons.
From 3d 4d series, a general trend is observed but not from 4d 5d series because of the incorporation of the 14 lanthanides elements between La and Hf. The third period of transition elements has the highest ionization energy. This reflects the fact that increase in radius due to addition of extra shell is compensated by the decrease in radius due to lanthanide contraction.
The radius of 4d and 5d-elements more or less remains the same. Due to this Zeff of elements of 5d series is higher, which results in high ionization energy of the 5d-elements of transition series.

Formation of complex compounds

The transition elements have characteristic tendency to form coordination compounds with Lewis bases that is with groups that are able to donate an electron pair. Cobalt forms more complexes than any other element and forms more compounds than any other element after carbon.
Description: 50443.png
Description: 50452.png

Color of complex compounds

Many ionic and covalent compounds of transition elements are colored. In contrast, compounds of the s- and p-block elements are almost always white. When light passes through a material, it is deprived of those wavelengths that are absorbed. If the wavelength of the absorption occurs in the visible region of the spectrum, the transmitted light is colored with the complementary color to the color of the light absorbed. Absorption in the visible and UV regions of the spectrum is caused by changes in electronic energy. Thus, the spectra are sometimes called electronic spectra.

Magnetic properties

Compounds of the transition elements exhibit characteristic magnetic behavior. Those which are attracted by a magnetic field are termed as paramagnetic. Those which are repelled by a magnetic field are called diamagnetic. Paramagnetic species have unpaired electrons in their electronic configuration. Diamagnetic substances are those in which electrons are fully paired.
The spin magnetic moment is measured in units of Bohr magneton. The spin magnetic moment is given by Description: 50459.png in BM, where n is the number of unpaired electrons.

Catalytic properties

Transition metals and their compounds act as good catalysts for a variety of reactions. The presence of empty d-orbitals enables them to form various intermediates during a reaction, thus providing a reaction path with lower activation energy for the reaction.
Many transition metals and their compounds have catalytic properties. A few of them are listed in the following table:
Used as the ZieglerNatta catalyst in the production of polythene.
Converts SO2 into SO3 in the contact process for making H2SO4.
Used as a catalyst to decompose KClO3 to give O2.
Promoted iron is used in the HaberBosch process for making NH3.
Formerly used for SO2 SO3 in the contact process for making H2SO4.
Raney nickel is used in numerous reduction processes (e.g., manufacture of hexamethylenediamine, production of H2 from NH3, reducing anthraquinone to anthraquinol in the production of H2O2).

Test Your Skills Now!
Take a Quiz now
Reviewer Name