d and f Block Elements — Revision Notes

⚡ 30-Second Revision

d-block (Transition Elements): — $(n-1)d^{1-10} ns^{1-2}$. Exceptions: Cr ($3d^5 4s^1$), Cu ($3d^{10} 4s^1$).
f-block (Inner Transition Elements): — Lanthanoids ($[Xe] 4f^{1-14} 5d^{0-1} 6s^2$), Actinoids ($[Rn] 5f^{1-14} 6d^{0-1} 7s^2$).
Variable Oxidation States: — Due to close energy of $(n-1)d$ and $ns$ orbitals.
Magnetic Moment: — $\mu = \sqrt{n(n+2)}\,\text{BM}$ (n = unpaired electrons).
Color: — Due to d-d transitions (d-block) or f-f transitions (f-block).
Lanthanoid Contraction: — Decrease in $Ln^{3+}$ radii due to poor 4f shielding. Consequences: Zr/Hf similar radii.
$K_2Cr_2O_7$: — Orange, Cr in $+6$ state, strong oxidizing agent (acidic: $Cr_2O_7^{2-} \to Cr^{3+}$).
$KMnO_4$: — Purple, Mn in $+7$ state, strong oxidizing agent (acidic: $MnO_4^- \to Mn^{2+}$).

2-Minute Revision

The d-block elements, or transition metals, are characterized by partially filled d-orbitals in their ground or common ionic states, leading to variable oxidation states, paramagnetism, and colored compounds.

Remember exceptions like Cr and Cu for electronic configurations. The spin-only magnetic moment is calculated using $\mu = \sqrt{n(n+2)}$ BM, where 'n' is the number of unpaired electrons. Color arises from d-d transitions.

The f-block elements are inner transition metals, divided into lanthanoids (4f) and actinoids (5f). Lanthanoids primarily show a +3 oxidation state and exhibit lanthanoid contraction, a significant decrease in atomic/ionic radii due to poor 4f shielding, making elements like Zr and Hf have similar sizes.

Actinoids are all radioactive and show a wider range of oxidation states due to the comparable energies of 5f, 6d, and 7s orbitals. Key compounds like $K_2Cr_2O_7$ (orange, Cr in +6) and $KMnO_4$ (purple, Mn in +7) are strong oxidizing agents, especially in acidic media, and their redox reactions are frequently tested.

5-Minute Revision

Let's quickly review the d and f block elements, focusing on high-yield NEET concepts. d-Block Elements (Transition Metals) have the general electronic configuration $(n-1)d^{1-10} ns^{1-2}$. Crucial exceptions are Chromium ($[Ar] 3d^5 4s^1$) and Copper ($[Ar] 3d^{10} 4s^1$).

They exhibit variable oxidation states because the $(n-1)d$ and $ns$ orbitals are very close in energy, allowing both to participate in bonding. For example, Manganese shows states from $+2$ to $+7$.

Most transition metal ions are paramagnetic due to unpaired d-electrons; their spin-only magnetic moment is $\mu = \sqrt{n(n+2)}$ BM. They form colored compounds due to d-d electronic transitions, where electrons absorb specific wavelengths of light to jump between split d-orbitals.

Ions with $d^0$ or $d^{10}$ configurations are typically colorless and diamagnetic. Transition metals also act as catalysts and form alloys and interstitial compounds.

f-Block Elements (Inner Transition Elements) are divided into Lanthanoids (4f series) and Actinoids (5f series). Lanthanoids have a general configuration of $[Xe] 4f^{1-14} 5d^{0-1} 6s^2$ and predominantly show a $+3$ oxidation state.

The most significant feature is Lanthanoid Contraction, a steady decrease in atomic/ionic radii from Ce to Lu, caused by the poor shielding effect of 4f electrons. This contraction leads to similar radii for elements in the second and third transition series (e.

g., Zr and Hf). Actinoids have a configuration of $[Rn] 5f^{1-14} 6d^{0-1} 7s^2$. They are all radioactive and exhibit a wider range of oxidation states (up to $+7$) than lanthanoids, due to the comparable energies of 5f, 6d, and 7s orbitals.

Actinoid contraction is more pronounced than lanthanoid contraction.

Finally, remember the chemistry of **Potassium Dichromate ($K_2Cr_2O_7$) and Potassium Permanganate ($KMnO_4$)**. $K_2Cr_2O_7$ is orange, contains Cr in $+6$ oxidation state, and is a strong oxidizing agent in acidic medium, reducing to green $Cr^{3+}$. $KMnO_4$ is purple, contains Mn in $+7$ oxidation state, and is a powerful oxidizing agent, reducing to colorless $Mn^{2+}$ in acidic medium, $MnO_2$ in neutral/weakly basic, and $MnO_4^{2-}$ in strongly basic medium.

Prelims Revision Notes

d-Block Elements (Transition Elements)

Definition: — Elements with partially filled $(n-1)d$ orbitals in ground state or common oxidation states. Groups 3-12.
Electronic Configuration: — General: $(n-1)d^{1-10} ns^{1-2}$.

* Exceptions: Cr ($[Ar] 3d^5 4s^1$), Cu ($[Ar] 3d^{10} 4s^1$). * Ions: Remove $ns$ electrons first, then $(n-1)d$.

Properties:

* Metallic Character: All are metals, high melting/boiling points. * Atomic/Ionic Radii: Decrease across period, less sharp than s/p-block. 3rd series elements (e.g., Hf) have similar radii to 2nd series (e.

g., Zr) due to lanthanoid contraction. * Ionization Enthalpy: Irregular increase across period. * Variable Oxidation States: Due to close energy of $(n-1)d$ and $ns$ orbitals. Highest for Mn ($+7$).

* Magnetic Properties: Paramagnetic (unpaired electrons), Diamagnetic (all paired). Spin-only magnetic moment: $\mu = \sqrt{n(n+2)}\,\text{BM}$. * Color: Most compounds are colored due to d-d transitions.

$d^0$ or $d^{10}$ ions are colorless (e.g., $Sc^{3+}$, $Ti^{4+}$, $Zn^{2+}$). * Catalytic Properties: Due to variable oxidation states and large surface area (e.g., Fe, V$_2$O$_5$, Ni). * Complex Formation: Form numerous coordination compounds.

* Interstitial Compounds: Formed with small non-metals (H, C, N, B). * Alloy Formation: Due to similar atomic sizes.

Important Compounds:

* **Potassium Dichromate ($K_2Cr_2O_7$):** Orange, Cr in $+6$ state. Strong oxidizing agent in acidic medium ($Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O$). * **Potassium Permanganate ($KMnO_4$):** Purple, Mn in $+7$ state. Strong oxidizing agent. * Acidic: $MnO_4^- + 8H^+ + 5e^- \to Mn^{2+} + 4H_2O$. * Neutral/Weakly Basic: $MnO_4^- + 2H_2O + 3e^- \to MnO_2 + 4OH^-$. * Strongly Basic: $MnO_4^- + e^- \to MnO_4^{2-}$ (green).

f-Block Elements (Inner Transition Elements)

Lanthanoids (4f series): — Ce (58) to Lu (71).

* Configuration: $[Xe] 4f^{1-14} 5d^{0-1} 6s^2$. * Oxidation States: Primarily $+3$. Some $+2$ ($Eu^{2+}$, $Yb^{2+}$) and $+4$ ($Ce^{4+}$) for stable $f^0, f^7, f^{14}$ configurations. * Lanthanoid Contraction: Steady decrease in $Ln^{3+}$ radii due to poor shielding by 4f electrons. Consequences: similar radii of Zr and Hf. * Color: Many $Ln^{3+}$ ions are colored (f-f transitions), generally pale.

Actinoids (5f series): — Th (90) to Lr (103).

* Configuration: $[Rn] 5f^{1-14} 6d^{0-1} 7s^2$. * Radioactivity: All are radioactive. * Oxidation States: Wider range than lanthanoids (e.g., $+3, +4, +5, +6, +7$) due to comparable energies of 5f, 6d, 7s orbitals. * Actinoid Contraction: More pronounced than lanthanoid contraction. * Reactivity: Generally more reactive than lanthanoids.

Vyyuha Quick Recall

To remember the common oxidation states of the first transition series elements (Sc to Zn), think: Strong Tigers Very Cruel Men Fear Copper Nickels Zinc.

This helps recall the order. For oxidation states, remember the general trend: start low, peak in the middle (Mn +7), then decrease.

Another one for Lanthanoid Contraction consequences: 'Zebras Have Nearly The Same Radii' for Zr-Hf, Nb-Ta, Mo-W having similar radii.