d and f Block Elements

Definition

A transition element is defined as an element that has a partially filled d-orbital in its ground state or in any of its common oxidation states.

Explanation

Think of the periodic table as a house. The s-block and p-block are the outer rooms, but the d-block is the central hallway that connects them. They represent a transition in properties from highly reactive metals (s-block) to non-metals (p-block).

• Occupies groups 3 to 12.
• All are metals (hard, high melting points, good conductors).
• They form colored ions and show variable oxidation states.

Examples

• Iron (Fe): Essential for construction and biological functions like hemoglobin.
• Copper (Cu): Crucial for electrical industries.

Real-Life Use: Catalysis

In automotive Catalytic Converters, transition metals like Platinum (Pt), Palladium (Pd), and Rhodium (Rh) act as catalysts to convert toxic gases (like CO) into less harmful substances like \(CO_2\) and \(N_2\).

A. Atomic and Ionic Radii

As you move left to right across a period, the atomic radius generally decreases due to increased nuclear charge. However, in the middle, the decrease slows down due to the shielding effect of the inner \((n-1)d\) electrons.

B. Oxidation States

Transition metals are highly flexible because the energy difference between \((n-1)d\) and \(ns\) orbitals is very small. For example, Manganese (Mn) can show oxidation states from +2 to +7.

C. Magnetic Properties

Most transition metal compounds are paramagnetic. If a substance has unpaired electrons, it is attracted to a magnetic field; if all are paired, it is diamagnetic.

D. Color in Transition Metal Ions

Colors arise from d-d transitions. When light hits the ion, an electron jumps to a higher-energy d-orbital, absorbing specific wavelengths and leaving the complementary color visible.

Potassium Dichromate (\(K_2Cr_2O_7\))

A strong oxidizing agent prepared from Chromite ore (\(FeCr_2O_4\)).

1. Fusion of Chromite ore with \(Na_2CO_3 \rightarrow\) Sodium chromate.
2. Acidification $\rightarrow$ Sodium dichromate.
3. Reaction with \(K_2SO_4 \rightarrow K_2Cr_2O_7\).

Potassium Permanganate (\(KMnO_4\))

A powerful, deep purple oxidizing agent prepared from Pyrolusite ore (\(MnO_2\)). It involves fusing \(MnO_2\) with KOH in air to form \(K_2MnO_4\) (green), followed by oxidation to \(KMnO_4\).

A. Lanthanoids (4f series)

• Most common oxidation state is +3.
• Lanthanoid Contraction: The steady decrease in atomic/ionic radii due to poor shielding by \(4f\) electrons. This makes 4d and 5d elements (like Zr and Hf) similar in size.

B. Actinoids (5f series)

• Show a wider range of oxidation states (+3 to +7) because \(5f, 6d,\) and \(7s\) levels are close in energy.
• All actinoids are radioactive.

Formula

$$\mu = \sqrt{n(n+2)} \text{ BM}$$

(Where \(n\) = number of unpaired electrons and BM = Bohr Magnetons)

Numerical Problem

Calculate the spin-only magnetic moment of \(Fe^{2+}\) (Atomic number of \(Fe = 26\)).

Step-by-Step Solution:
1. Neutral configuration: Fe = [Ar] 3d⁶ 4s²
2. Fe²⁺ configuration: [Ar] 3d⁶ (removed 2e⁻ from 4s)
3. Unpaired electrons (n): 
   In 3d⁶, we have 5 orbitals. 
   5 electrons enter singly, 1 pairs up.
   Unpaired electrons (n) = 4.
4. Apply formula:
   μ = √[4(4 + 2)]
   μ = √[4(6)] = √24
   μ ≈ 4.89 BM

Final Answer: 4.89 BM
        

1. Which of the following is a transition element?
   a) Zn b) Cd c) Hg d) Fe
   Ans: d
2. The most common oxidation state of lanthanoids is:
   a) +2 b) +3 c) +4 d) +5
   Ans: b
3. Lanthanoid contraction is due to:
   a) Increase in nuclear charge b) Poor shielding of 4f electrons c) Both a and b d) None
   Ans: c
4. The color of \(KMnO_4\) is due to:
   a) d-d transition b) Charge transfer c) f-f transition d) None
   Ans: b
5. Which element shows the maximum number of oxidation states?
   a) Fe b) Mn c) Cr d) V
   Ans: b

1. Why are Zinc, Cadmium, and Mercury not considered transition elements?
   Transition elements must have partially filled d-orbitals. Zn, Cd, and Hg have completely filled \(d^{10}\) configurations in their ground and common ionic states.
2. Explain Lanthanoid Contraction and its consequences.
   It is the steady decrease in ionic radii of lanthanoids due to poor shielding by \(4f\) electrons. This makes elements in the 2nd and 3rd transition series similar in size, making separation hard.
3. Why do transition metals show variable oxidation states?
   Because the energy difference between \((n-1)d\) and \(ns\) orbitals is very small, allowing electrons from both to participate in bonding.
4. Predict the magnetic nature of \(Sc^{3+}\) (Atomic No. 21).
   \(Sc\) is \([Ar] 3d^1 4s^2\). \(Sc^{3+}\) is \([Ar]\) (no electrons in d-shell). It is diamagnetic.

• d-block: Groups 3-12, variable oxidation, colored ions, paramagnetic.
• f-block: Lanthanoids (+3, 4f) and Actinoids (Radioactive, 5f).
• Lanthanoid Contraction: Poor \(4f\) shielding $\rightarrow$ smaller size.

Mnemonic for 3d series:
"Science Teacher Vinay Cried Man FeCo Nice Cup Zinc"
(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)