Electronic Configuration of the d-block Elements

The d-block elements are those that can be found in the contemporary periodic table from the third to the twelfth groups. These elements’ valence electrons are located in the d orbital. d-block elements are sometimes known as transition elements or transition metals. The 3d, 4d, and 5d orbitals are represented by the first three rows of the d block elements, respectively.

d block elements are those that have electrons (1 to 10) in the d-orbital of the penultimate energy level and in the outermost orbital (1-2). Despite the fact that electrons do not fill the ‘d’ orbital in group 12 metals, their chemistry is comparable to that of the preceding groups in many aspects, and they are thus classified as d block elements. Metallic properties like malleability and ductility, high electrical and thermal conductivity, and good tensile strength are typical of these elements. The d block is divided into four series, each of which corresponds to the filling of 3d, 4d, 5d, or 6d orbitals. Each series has ten elements that occupy the ‘d’ orbital.

• 3d: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn
• 4d: Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd
• 5d: La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg
• 6d: incomplete.

The d-block Elements

Groups 4–11 are made up of transition elements. Transition elements include scandium and yttrium from Group 3, which have a partially filled d subshell in the metallic form. Elements in the 12 columns of the d block, such as Zn, Cd, and Hg, have completely filled d-orbitals and are hence not considered transition elements. Transition Elements get their name from the fact that they are placed between s and p block elements and have characteristics that transition between them. So, while all transition metals are d block elements, not all transition metals are transition elements.

Properties of Transition Metals

• Between their (n+1) s and (n+1) p sub-orbitals, electrons are added to the ‘d’ sub-orbitals.
• In the periodic table, it is located between the s and p block elements.
• The differences in properties between s and p-block elements.

In the three series of transitions,

1. The ionisation energy of elements gradually grows across a row.
2. Density, electronegativity, electrical, and thermal conductivities increase from the left of the 3d series to the right corner of the 5d transition elements, whereas enthalpies of hydration of metal cations decrease.

This suggests that the transition metals are becoming less reactive and more “noble” in nature. Metals (Pt, Au) in the lower right corner of the d block have such high ionisation energies, increasing electronegativity, and decreasing low enthalpies of hydration that they are commonly referred to as “noble metals.”

Electronic Configuration of d-Block Elements

The electrical configuration of D block elements is (n-1)d^1-10 ns^1-2. Half-filled orbitals and entirely filled d orbitals are both stable for these elements. The electronic configuration of chromium, which includes half-filled d and s orbitals in its configuration – 3d⁵ 4s¹ – is an example of this. Copper’s electronic configuration is another example. Copper has a 3d¹⁰ 4s¹ electronic arrangement rather than a 3d⁹ 4s². The relative stability of the entirely filled d orbital can be due to this. In both their ground and general oxidation states, zinc, mercury, cadmium, and copernicium have totally filled orbitals. As a result, these metals aren’t classified as transition elements, while the rest are classified as d block elements.

• Period 4, transition elements’ electronic configuration is (Ar) 4s^1-2 3d^1-10.
• Period 5, transition elements’ electronic configuration is (Kr) 5s^1-2 4d^1-10.
• Period 6, transition elements’ electronic configuration is (Xe) 4s^1-2 3d^1-10.

According to the Aufbau principle and Hund’s rule of multiplicity, electrons are added to the 3d subshell from left to right along the period.

Element	Electronic Configuration
Sc	4s2 3d1
Ti	4s2 3d2
V	4s2 3d3
Cr	4s1 3d5
Mn	4s2 3d5
Fe	4s2 3d6
Co	4s2 3d7
Ni	4s2 3d8
Cu	4s1 3d10
Zn	4s2 3d10

All of the series have anomalies, which can be explained by the following considerations.

1. The distance between the ns and (n-1) d orbitals in terms of energy.
2. Half-full orbitals are more stable than partially filled orbitals.
3. Pairing energy for electrons in s-orbitals.

Chromium has a 4s¹ 3d⁵ electron configuration rather than a 4s² 3d⁴ electron configuration, while copper has a 4s¹ 3d¹⁰ electron configuration rather than a 4s² 3d⁹. The stability of half-full orbitals relative to partly filled orbitals explains these oddities in the first transition series.

From niobium onwards, electron presence in d orbitals appears to be preferred over electron sharing in s orbitals in the second series of transition metals. The electron can choose between sharing in the s orbital or being stimulated to the d orbital from the available s and d orbitals. Obviously, the choice is determined by the amount of repulsive energy overcome during sharing and the energy difference between the s and d-orbitals.

Because the s and d-orbitals have about the same energy in the second series, electrons choose to occupy the d-orbital. As a result, s-orbital has only one electron in niobium. Transition metals of the third series, on the other hand, have a higher number of paired s configurations, even at the expense of half-filled orbitals. This series follows the filling of 4f orbitals and the lanthanide contraction that follows.

Because of the smaller size, the ‘f’ electron provides a lot of shielding for the d orbitals. The energy gap between the s and 5d orbitals is increased as a result of the shielding, and the pairing energy is less than the excitation energy. Despite the stability provided by half-filled orbitals, tungsten does not allow for electron excitation.

Sample Questions 

Question 1: What are the transition metals’ metallic properties?

Solution:

Malleability, ductility, high tensile strength, and metallic lustre are all characteristics of transition metals. They have a tendency to crystallise and are generally good heat and electricity conductors. Trends in the transition elements’ metallic properties, on the other hand, can be seen. Elements like chromium and molybdenum are among the hardest transition metals because they contain a large amount of unpaired electrons.

Question 2: What are the uses of transition metals?

Solution:  

Nickel is a transition metal that is largely utilised in the production of stainless steel. Copper, a transition metal with high tensile strength, malleability, ductility, and electrical conductivity, is commonly used in electrical wire.

Question 3: Why are some transition metals referred to as noble metals?

Solution:

Noble metals are elements in the d-block of the modern periodic table’s lower right corner (such as gold, silver, and platinum). These metals are particularly unreactive due to their low hydration enthalpies and high ionisation enthalpies.

Question 4: What are inner transition elements?

Solution:

The periodic table divides elements into two groups: lanthanides and actinides. Inner transition elements make up a total of 30 elements in these categories. They are often positioned behind the periodic table’s core section.

Question 5: Why are all the transition elements metals?

Solution:

Transition elements are all metals because their outermost shells have only two electrons. Due to strong metallic linkages, they are also malleable, hard, and ductile.