D block elements are found on the modern periodic table from the third to the twelfth group. Their valence electrons are placed in the d orbital. D block elements are also known as transition elements or transition metals. Let us take a detailed look at the d
block on the modern periodic table.
What are D Block Elements?
The d block elements are those elements that have electrons (1-10) filled in the d orbital of the penultimate energy level and also in the s orbital (1-2) are classified as D block elements. Group 12 does not have elements in which electrons fill the d orbital, but they are still grouped in the d block because of similar chemical properties.
Given below is a list of d block elements:
- Scandium (Sc)
- Titanium (Ti)
- Vanadium (V)
- Chromium (Cr)
- Manganese (Mn)
- Iron (Fe)
- Cobalt (Co)
- Nickel (Ni)
- Copper (Cu)
- Zinc (Zn)
- Yttrium (Y)
- Zirconium (Zr)
- Niobium (Nb)
- Molybdenum (Mo)
- Technetium (Tc)
- Ruthenium (Ru)
- Rhodium (Rh)
- Palladium (Pd)
- Silver (Ag)
- Cadmium (Cd)
- Lanthanum (La)
- Hafnium (Hf)
- Tantalum (Ta)
- Tungsten (W)
- Rhenium (Re)
- Osmium (Os)
- Iridium (Ir)
- Platinum (Pt)
- Gold (Au)
- Mercury (Hg)
- Actinium (Ac)
- Rutherfordium (Rf)
- Dubnium ( Db)
- Seaborgium (Sg)
- Bohrium (Bh)
- Hassium (Hs)
- Meitnerium (Mt)
- Darmstadtium (Ds)
- Roentgenium (Rg)
- Copernicium (Cn)
Why Are D Block Elements Called Transition Metals?
D block elements have properties and position that transition between s and p block elements. The main groups of transition elements are four to eleven. However, scandium and yttrium of group three are also considered transition metals due to their partially filled d subshell in the metallic state. Elements like zinc and mercury have filled d subshells and are not considered transition metals.
All transition metals are d block elements but not all d block elements are transition metals.
Electronic Configuration of D Block Elements
The general configuration of D block elements is (n - 1)d1-10ns1-2.
Half-filled orbitals and filled d orbitals can provide stability to these elements.
Let us look at the electronic configuration of transition series according to the Aufbau principle and Hund’s rule of multiplicity.
First Transition series
Second Transition series
Third transition series
Anomalies in all the series can be attributed to the following reason:
- The energy gap between ns and (n - 1)d orbitals
- Pairing energy for electrons in the s orbital
- Stability of half-filled orbitals to the partly filled orbitals
The electronic configuration of chromium is 4s13d5 instead of 4s23d4 and that of copper is 4s13d10 instead of 4s23d9. These anomalies can be understood from the stability of half-filled orbitals to the partially filled ones.
Properties of Transition Metals
Transition metals have many properties that are not found in other metals. This can be attributed to partially filled d orbitals. Let us take a look at these properties:
- Due to the low energy gap between different possible oxidation states, compound formation occurs in many oxidation states
- Many paramagnetic compounds are formed due to the presence of an unpaired electron
- Most transition metals can be bound to many different ligands allowing for a wide range of transition metal complexes.
- Coloured compounds, which occur due to charge transfer.
Charge Transfer Transition - an electron may shift from a predominantly legendary orbit to a metal orbit. This gives rise to a ligand to metal charge transfer transition. Coloured compounds generally occur when metals are in a higher oxidation state.
Atomic and Ionic Radii Of D Block Elements
Atomic and ionic radii of elements of all three transition series of the d block decrease rapidly from column three to six, remain steady from column three to ten and start increasing from column eleven to twelve.
Since electrons occupy a higher orbital, the radius of third series elements is supposed to be higher than second series elements. However, the radii of the elements of the second and third series elements are almost the same.
In the third series, 5d orbitals are filled only after the 4f orbitals are filled. Due to this, the effective nuclear charge increases by 14 units. This higher nuclear charge leads to shrinkage of radii known as Lanthanide contraction.
The increase in the effective nuclear charge neutralizes the increase in radii that might occur due to higher orbitals.
Properties of D Block Elements
- Ionization Energy of D Block Elements - Ionization energy of d block elements is larger than s block and smaller than p block elements. In the first series, except for chromium and copper, the first ionization energy involves removal from the filled s orbital. Among them, the ionization energy of d block elements increases with the increase in atomic number till iron.
- Metallic Character - D block elements show the metallic character of high tensile strength, malleability, ductility, electrical and thermal conductivity, metallic luster, etc. d block elements are very hard and have high enthalpy and low volatility except for copper. Hardness increases with the number of unpaired electrons. The group 12 elements (zinc, cadmium, and mercury) are exceptions here.
Oxidation States Of D Block Elements
Oxidation state is the hypothetical state where the atom appears to gain or lose electrons more than the usual valency state.
Since the energy difference between s and d orbital is small, both the electrons can be included in ionic and covalent bond formation. This makes them exhibit multiple valency states (oxidation states).
Each transition element can exhibit a minimum oxidation state about the number of s electrons. transition elements can also exhibit a maximum oxidation state equivalent to the total number of electrons in both s and d orbitals combined. Oxidation states that lie in between can also be exhibited.
Why Do D Block Elements Have High Melting And Boiling Points?
Unpaired electrons and partially filled or empty d orbitals form covalent bonds along with the metallic bonds by s electrons. Due to such strong bonds, D block elements have high melting and boiling points. This trend continues until the d5 configuration and reduces as more electrons in the d orbital get paired.
The Liquid Metal
The only metal that exists in a liquid state at room temperature is mercury. 6s valence electrons of mercury are so closely pulled by the nucleus (lanthanide contraction) that the outer electrons are less involved in metallic bonding.
Noble Metals in Transition Elements
The ionization energies of elements in the three transition series increase very slowly across a given row. From the 3rd series to the right corner 5d transition elements, density, electronegativity, electrical and thermal conductivities increase, while enthalpies of hydration of the metal cations decrease in magnitude.
This indicates that transition metals become less reactive gradually and nobler. The relatively high ionization energies, increasing electronegativity, and decreasing low enthalpies of hydration make metals in the lower right corner of the d block so unreactive that they are usually called noble metals.
Electrode Potential Of D Block Elements
Relative stabilities of transition metal ions in different oxidation states in the aqueous medium can be estimated from the electrode potential data. The oxidation state of a cation for which △H(△HSub + IE + △Hhyd) or E° is more negative will be more stable.
Transition metals elements have low E° as compared to first and second group elements. E° becomes less negative along with the series, showing higher stability of the reduced state.
Magnetic Properties Of D Block Elements
There are three types of elements when it comes to magnetic properties. These are:
- Diamagnetic: Diamagnetic elements are repelled by a magnet. This is caused by paired electrons.
- Paramagnetic: Paramagnetic elements are attracted to a magnet. This is caused by unpaired electrons
- Ferromagnetic: ferromagnetic elements can retain a magnetic nature even in the absence of a magnet. This is caused by unpaired electrons aligned together.
Learning Tips - How to Learn Periodic Table
Unpaired electrons determine the magnetic nature of D block elements. Unpaired electrons contribute to ‘orbital magnetic moment’ and ‘spin magnetic moment’.
For the 3d series the orbital magnetic moment is negligible. The following formula gives the approximate spin only magnetic moment:
μ= √[4s(s+1)] = √[n(n+1)]BM
Where is the total spin and n is the number of unpaired electrons? The unit is BM (Bohr Magneton).
For the higher series of the d block, the actual magnetic moment includes components from the orbital magnetic moment along with the spin magnetic moment.
Let us take a look at the magnetic moment of some ions in the table below
No. of Unpaired Electrons
Complex Formation Tendency Of D Block Elements
Complex compounds are those compounds in which several neutral molecules are bound to a metal. Metals in the d block make many complex compounds due to their small ionic size, high charge, and related availability of d orbitals for bond formation.
Transition metals and their ions with higher nuclear charge and smaller size can attract electrons and lone pairs of electrons from anions and neutral molecules in their empty d orbitals for bond formations.
Important compounds of D Block Elements
The D block elements form some very important compounds that are used generously in industries. Let us take a look.
K2Cr2O7 (Potassium Dichromate)
Potassium dichromate is a vital compound in the leather industry. Azo compounds are also processed using this compound as an oxidant.
KMnO4 (Potassium Permanganate)
Potassium permanganate is dark purple in colour. it is generally diamagnetic in nature and sometimes shows paramagnetic properties depending on the temperature.
This is a brief description of the D block elements of the periodic table. Learning the periodic table according to blocks is always a good idea. Happy Learning!
Class 12 (PCM)