1. Meet the Actinoids (Th → Lr) 🚀
The actinoids are fourteen silvery-white, radioactive elements running from thorium (Th, Z = 90) to lawrencium (Lr, Z = 103). Their study is tricky because later members exist only in nanogram amounts and can decay in minutes! :contentReference[oaicite:0]{index=0}
2. Electronic Configurations 🔬
- All actinoids have an outer shell of \(7s^{2}\) electrons plus a variable mix of \(5f\) and \(6d\) electrons. :contentReference[oaicite:1]{index=1}
- Electrons fill the \(5f\) subshell after thorium, ending with a full \(5f^{14}\) in Lr. :contentReference[oaicite:2]{index=2}
- Special “half-filled” and “filled” stabilities pop up just like in the lanthanoids.
• Americium: \(\text{[Rn] }5f^{7}\,7s^{2}\)
• Curium: \(\text{[Rn] }5f^{7}\,6d^{1}\,7s^{2}\) :contentReference[oaicite:3]{index=3} - Because \(5f\) orbitals stick out more than \(4f\), these electrons can join in bonding, giving richer chemistry than the lanthanoids. :contentReference[oaicite:4]{index=4}
3. Ionic Sizes & “Actinoid Contraction” 📉
Just as lanthanoids shrink across the series, actinoid atoms and their \(M^{3+}\) ions get smaller left-to-right. The contraction is even stronger because \(5f\) electrons shield the nucleus poorly. :contentReference[oaicite:5]{index=5}
4. Oxidation States 🔋
+3 is common to all actinoids, but early members climb higher:
| Element | Typical Oxidation States |
|---|---|
| Ac | +3 |
| Th | +3, +4 |
| Pa | +3, +4, +5 |
| U | +3, +4, +5, +6 |
| Np | +3 → +7 |
| Pu | +3 → +6 |
| Am, Cm | +3 → +6 |
| Bk, Cf | +3, +4 |
| Es → Lr | +3 |
Notice the “peak” at neptunium (+7) and the steady slide back to +3.
5. Chemical Behaviour ⚗️
- Highly reactive, especially as powders.
- Boiling water turns them into a mix of oxide and hydride. :contentReference[oaicite:6]{index=6}
- They combine readily with non-metals at moderate temperatures.
- Hydrochloric acid dissolves them; nitric acid often forms a protective oxide coat; alkalies leave them alone. :contentReference[oaicite:7]{index=7}
6. Magnetic & Energetic Notes 🧲
- Magnetic behavior tracks the number of unpaired \(5f\) electrons but shows even trickier patterns than the lanthanoids. :contentReference[oaicite:8]{index=8}
- Early actinoids have lower ionisation energies than matching lanthanoids because \(5f\) electrons shield better, making outer electrons easier to remove. :contentReference[oaicite:9]{index=9}
7. How They Compare with Lanthanoids 🔄
- Both families shrink across the period, but actinoids shrink faster.
- Early actinoids show wide oxidation ranges; later ones mimic lanthanoid “+3-only” chemistry.
- Because \(5f, 6d,\) and \(7s\) orbitals are close in energy, actinoids display richer bonding and variable structures. :contentReference[oaicite:10]{index=10}
🎯 High-Yield Ideas for NEET
- Actinoid contraction is larger than the lanthanoid contraction—remember why (poor \(5f\) shielding).
- Variable oxidation states, peaking at +7 for neptunium, then sliding back to +3.
- All actinoids start with a \(\boldsymbol{7s^{2}}\) pair and fill the \(5f\) subshell after thorium.
- Reactivity pattern: hot water → oxide + hydride; HCl dissolves; \( \text{HNO}_3 \) passivates.
- Magnetic and bonding quirks stem from more “exposed” \(5f\) electrons.
😊 Happy studying, and may these actinoid nuggets power up your NEET prep!
