D & F Block Elements - Chemistry Class 12

D block elements are located between the S block and P block in the periodic table.
F block elements are located outside the main table.

D block elements are defined as those in which the valence electron enters the $(n-1)d$ orbital.
$(n-1)$ refers to the penultimate shell (the shell before the outermost shell).
Example: If the outermost shell (n) is 4 (4s), the electron fills the 3d orbital.
General electronic configuration: $ns^{1-2} (n-1)d^{1-10}$

Some elements, like chromium (Cr), have exceptional electronic configurations.
Chromium (Cr): Atomic number 24. Expected configuration: $4s^2 3d^4$ . Actual configuration: $4s^1 3d^5$ (one electron jumps from 4s to 3d for a half-filled d orbital).
This exception leads to the general configuration being written as $ns^{1-2}$ .

Transition elements are defined as elements with incomplete d orbitals in their ground state or common oxidation state.
Example: Manganese (Mn), atomic number 25, configuration: $4s^2 3d^5$ . The d orbital is incomplete, making it a transition element.
Example: Iron (Fe), atomic number 26, configuration: $4s^2 3d^6$ . The d orbital is incomplete, making it a transition element.
Example: Zinc (Zn), atomic number 30, configuration: $4s^2 3d^{10}$ . D orbital is complete.
Stable oxidation state of Zinc: $Zn^{+2}$ which has a configuration of $4s^0 3d^{10}$ . The d orbital remains complete.

Zinc (Zn), Cadmium (Cd), and Mercury (Hg) are d-block elements but not transition elements because their d orbitals are complete in both their ground state and stable oxidation states.

Melting point and enthalpy of atomization depend on the strength of the metallic bond.
Strength of metallic bond is directly proportional to the number of unpaired electrons.
More unpaired electrons lead to a stronger metallic bond, resulting in higher enthalpy of atomization and melting point.
Transition elements generally have high enthalpy of atomization and melting points due to many unpaired electrons.
Exception: Zinc (Zn) has the lowest enthalpy of atomization in the 3d series because it has no unpaired electrons.
Chromium (Cr) has the highest enthalpy of atomization in the 3d series because it has the maximum number of unpaired electrons (6 unpaired electrons: 5 in 3d and 1 in 4s).

Atomic size decreases from left to right across a period.
Atomic size increases from top to bottom within a group.
In transition elements, atomic size remains almost constant when moving from top to bottom, especially from 4d to 5d series, due to lanthanide contraction.
Lanthanide contraction: Poor shielding by 4f electrons leads to increased effective nuclear charge and a decrease in atomic size.
For 5d and 6d series elements it is known as actinoid contraction.

Zirconium (Zr) and Hafnium (Hf) have similar properties due to their similar size caused by lanthanide contraction.
Separating elements becomes difficult due to similar physical and chemical properties.
Density increases due to increasing mass but nearly constant volume.
Density = Mass / Volume

Paramagnetic: Attracted to magnetic field (due to unpaired electrons).
Diamagnetic: Repelled by magnetic field (no unpaired electrons).
Magnetic moment ( $\mu$ ) is determined by the number of unpaired electrons (n).
Spin-only formula for magnetic moment: $\mu = \sqrt{n(n+2)}$ Bohr magnetons (BM).
SI unit of magnetic movement is Bohr Magneton.
D block elements are generally paramagnetic due to unpaired electrons.
Exception: Zinc (Zn) is not paramagnetic because it has a full d orbital (no unpaired electrons).

Calculate the spin-only magnetic moment of $M^{+2}$ ion with atomic number 27.
1. Electronic configuration of M: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^7$
2. Electronic configuration of $M^{+2}$ : $1s^2 2s^2 2p^6 3s^2 3p^6 4s^0 3d^7$
3. Number of unpaired electrons (n) in $3d^7$ : 3
4. Magnetic moment: $\mu = \sqrt{3(3+2)} = \sqrt{15}$ Bohr magnetons.

D block elements form colored ions due to d-d transition.
Electrons jump from lower energy d orbitals to higher energy d orbitals by absorbing energy in the visible range.
When electrons fall back to lower energy levels, they emit radiation in the visible spectrum.
For colored ions:
- Incomplete d orbital (transition element).
- Unpaired electrons.
Salts of zinc are often white because zinc has a complete d orbital, preventing d-d transitions.

Transition elements easily form complex compounds due to:
- Small size and high ionic charge.
- Availability of empty d orbitals for accepting electron pairs from ligands.

Catalysts alter the rate of a reaction.
Transition elements are good catalysts because:
- They form intermediate compounds with reactants.
- They exhibit variable oxidation states.

Interstitial compounds are formed when small atoms (H, C, N) are trapped inside the crystal lattice of transition metals.
They are non-stoichiometric and chemically inert.
The size of the voids in D Block elements are of sufficient size that they can trap hydrogen, carbon and nitrogen inside them.

D block elements readily form alloys due to similar atomic sizes.
Conditions for alloy formation:
- Similar chemical properties.
- Atomic size difference should be within 5-15%.

Ionization enthalpy generally increases from left to right across a period and decreases from top to bottom within a group.
D block elements exhibit irregular variation in ionization enthalpy due to stability at $d^3$ , $d^5$ , and $d^{10}$ configurations.
- Regular means it's non uniform

Chromium (+2) is a stronger reducing agent than Iron (+2) because $Cr^{+2}$ (d4) readily converts to $Cr^{+3}$ (d3), which is more stable.
Metals of d block achieve their highest oxidation states in the form of oxides and fluorides because oxygen and fluorine are most electronegative substances.
$Manganese^{+3}$ is an oxidant . Chromium is a reducing agent because if $Cr^{+2}$ Oxidizes it becomes $Cr^{+3}$ = $d^3$ , on the other hand when $Mn^{+3}$ Accepts electron to make $Mn^{+2}$ it reaches the $d^5$ configuration
Non-transition elements have even numbers of unpaired electrons. Transition elements are stable at $d^3$ , $d^5$ and $d^{10}$ configurations
The E value of copper (Cu) is positive because even though it is fully filled in the +1 state, when it is +2, one electron remains unpaired using this unpaired electron dissolution takes place in water.
Scandium is a true transition element