What is a Transition Metal?
Transition Metals Definition - The d-block elements are called transition metal. The d-block consists of the elements that are lying in between the s and p blocks. The position of this block is between groups 2 and 13 in the periodic table. It starts from the fourth period onwards. In these elements, the outermost shell contains one or two electrons in their s-orbital but the last electron enters the last but one d subshell (n-1) d. The properties of the elements of this block generally lie between the elements of s block and p block.
Transition Elements List
The transition elements list contain the metals that have incompletely filled d-subshells in their ground state or any one of their oxidation states. Metals included in the transition elements list are:
Scandium (first transition element).
Titanium.
Vanadium.
Chromium.
Manganese.
Iron.
Cobalt.
Nickel.
Copper.
Zinc.
Yttrium.
Zirconium.
Niobium.
Molybdenum.
Technetium.
Ruthenium.
Rhodium.
Palladium.
Silver.
Cadmium.
Lanthanum.
Hafnium.
Tantalum.
Tungsten.
Rhenium.
Osmium.
iridium.
Platinum.
Gold.
Mercury.
Actinium.
Rutherfordium.
Hafnium.
Seaborgium.
Bohrium.
Hassium.
Meitnerium.
Darmstadtium.
Roentgenium.
Copernicium.
First Transition Series
The first transition series consists of elements from scandium, Sc (Z = 21) to zinc, Zn (Z = 30) i.e scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. The first transition element is scandium, in scandium, the 3d orbital starts filling up and its electronic configuration is [Ar] 4s2 3d1. As we move from scandium onwards, 3d orbitals get filled up more and more till the last element, zinc, in which the 3d orbitals are completely filled [Ar] 4s2 3d10.
Exceptional Electronic Configuration of Chromium (Cr) and Copper (Cu) in Transition Series
The configuration of chromium and copper are anomalous. We know that half-filled and filled electronic configurations have extra stability associated with them. Moreover, the energy difference between 3d and 4s orbitals is not large enough to prevent the electron from entering the 3d orbitals. Thus, to acquire increased stability, one of the 4s electrons goes to nearby 3d orbitals so that the 3d orbital becomes half-filled in the case of chromium and filled in the case of copper respectively. Therefore, the electronic configuration of chromium is [Ar] 3d5 4s1 rather than [Ar] 3d4 4s2 while that of copper is [Ar] 3d10 4s1 instead of [Ar] 3d9 4s2.
Second Transition Series
The 2nd transition series consists of elements from yttrium, Y (Z = 39) to cadmium, Cd (Z = 48), i.e., yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver and cadmium. This series involves the filling of 4d-orbitals.
Third Transition Series
This series consists of elements of lanthanum and from hafnium to mercury i.e., lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. In between Lanthanum and Hafnium there are fourteen elements called lanthanides which involve the filling of 4f-orbitals and do not belong to this series. The elements of the d-block third series involve the gradual filling of five d-orbitals. It may be noted that, in the second and third transition series, there are many anomalous configurations in comparison to those of the first transition series. These are accredited to the factors like nuclear electron and electron-electron forces.
Fourth Transition Series
It involves the filling of a 6d subshell starting from actinium (Z=89); which has the configuration 6d1 7s2. This fourth transition series in periodic table is incomplete as given in the table below:
General Characteristics of Transition Metals Elements are:
Nearly all the d-block transition elements possess metallic properties such as:
have high tensile strength.
Ductility.
Malleability.
High thermal conductivity.
Electrical conductivity.
Metallic lustre.
Except for mercury which is liquid at room temperature, other transition elements have typical metallic structures.
Transition elements possess a high melting point and high boiling points.
The value of heats of vaporisation is higher than the non-transition elements.
The transition elements have very high densities as compared to the metal of group 1 and 2nd (s block).
The first ionisation energies of d block elements are higher than those of s block elements but are lesser than those of p block elements.
Did You Know?
The fundamental difference in the electronic configuration of transition elements and representative elements is that in the representative elements the valence electrons are present only in the outermost shell. On the other hand, in the transition elements, the valence electrons are present in the outermost shell (ns) as well as the d orbital of the penultimate shell.
The ionization energy of chromium and copper have an exceptionally higher energy than those of their neighbours.
FAQs on Transition Metal
1. What are transition metals and where are they located in the periodic table?
Transition metals are elements that have an incompletely filled d-subshell in their ground state or in any of their common oxidation states. They are also known as the d-block elements. In the periodic table, they occupy the central block, positioned between the s-block (Groups 1 and 2) and the p-block (Groups 13 to 18), starting from the fourth period.
2. What are the key characteristics that define transition metals?
Transition metals exhibit a unique set of properties due to their electronic structure. Key characteristics include:
- Variable Oxidation States: They can show multiple oxidation states in their compounds.
- Formation of Coloured Ions: Their compounds are often brightly coloured due to d-d electron transitions.
- Catalytic Activity: Many transition metals and their compounds act as excellent catalysts.
- Formation of Complex Compounds: They have a strong tendency to form coordination complexes.
- High Density and Melting Points: They are typically hard, dense metals with high melting and boiling points.
3. Why are most transition metal compounds coloured?
The colour of transition metal compounds arises from a phenomenon called d-d transition. In the presence of ligands, the d-orbitals of the metal ion split into two different energy levels. When light falls on the compound, an electron from a lower energy d-orbital can absorb energy and get promoted to a higher energy d-orbital. The colour we perceive is the complementary colour of the light that was absorbed during this electron transition.
4. How do the unique electronic configurations of transition metals lead to their variable oxidation states?
Transition metals show variable oxidation states because the energy difference between the (n-1)d and ns orbitals is very small. Consequently, electrons from both the ns orbital and the (n-1)d orbital can participate in chemical bonding. For example, Manganese (Mn), with an electronic configuration of [Ar] 3d⁵ 4s², can lose the two 4s electrons for a +2 state, or lose additional d-electrons to show oxidation states up to +7.
5. Why is copper considered a transition metal despite having a completely filled d-orbital (3d¹⁰) in its ground state?
While copper has a 3d¹⁰ configuration in its ground state, it is classified as a transition metal because it can form a stable ion, Cu²⁺, in its +2 oxidation state. The electronic configuration of the Cu²⁺ ion is [Ar] 3d⁹, which features an incompletely filled d-orbital. As per the definition, an element is a transition metal if it has an incomplete d-subshell in its ground state or in any of its common oxidation states.
6. What are some important industrial applications of transition metals as catalysts?
Transition metals are vital catalysts in many industrial processes due to their ability to adopt multiple oxidation states. For example:
- Iron (Fe) is used as the catalyst in the Haber-Bosch process for manufacturing ammonia.
- Vanadium Pentoxide (V₂O₅) is used in the Contact process for the production of sulphuric acid.
- Nickel (Ni) is widely used for the hydrogenation of vegetable oils to produce margarine.
7. How are transition metals (d-block) different from inner transition metals (f-block)?
The primary difference lies in the orbital where the last electron enters.
- In transition metals (d-block), the differentiating electron enters the penultimate shell's d-orbital, i.e., the (n-1)d orbital. These elements are located in Groups 3-12 of the periodic table.
- In inner transition metals (f-block), the last electron enters the anti-penultimate shell's f-orbital, i.e., the (n-2)f orbital. These elements (Lanthanoids and Actinoids) are placed separately at the bottom of the periodic table.
