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IITJEE CHEMISTRY: Periodic Properties & Shielding Effect Visualizer

By

Ashish Kumar Bahekar

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APEX CLASS • IITJEE Inorganic Chemistry Lab

Periodic Properties & Shielding Effect Visualizer

Master Atomic Radii Trends, Lanthanide Contraction, Ionization Energy Traps, and Electron Affinity Exceptions!

🔬 Select a Size or Shielding Concept:
Atomic & Ionic Radii Trends Li Be B C N Size DECREASES across a period! Reason: Zeff increases, pulling electrons inward. Cation vs. Parent vs. Anion Size Na⁺ < Na < Na⁻ Cations lose a shell / Zeff ↑ (Smaller) Anions gain e⁻ / Zeff ↓ (Larger) +Ze Core e⁻ Shield Valence e⁻ Zeff Effective Nuclear Charge (Zeff) Zeff = Z – σ • Z = Actual Nuclear Charge (Atomic Number) • σ = Shielding / Screening Constant Shielding Power Order: s > p > d > f The Isoelectronic Series Trap (All have 10 electrons!) Golden Rule: For isoelectronic species, Size ∝ 1 / Z (More protons pulling on the same number of electrons = Smaller Size) N³⁻ Z=7 O²⁻ Z=8 F⁻ Z=9 Ne Z=10 Na⁺ Z=11 Mg²⁺ Z=12 Al³⁺ Z=13 All have 10 e⁻. Highest positive charge = Smallest radius! Radius Group → 3d Series 4d Series Zr 5d Series Hf The Lanthanide Contraction • Normally, Size increases down a group. • But 4d and 5d transition metals have nearly IDENTICAL radii! Why? Extremely poor shielding by 4f electrons. Zeff increases massively, shrinking the atom.
Atomic Radius Definition
Vanderwaal > Metallic > Covalent
Noble gases use Vanderwaal radius!
Slater’s Rule Shortcut
s/p valence shield = 0.35
(n-1) shell = 0.85, (n-2) = 1.00
Atomic Twins (JEE Faves)
Zr ≈ Hf & Nb ≈ Ta
Due to Lanthanide Contraction
Transition Metal Radii
Sc to Mn (↓), Fe Co Ni (≈), Cu Zn (↑)
Shielding eventually beats Zeff at the end.
⚡ Select an Energy Concept to Visualize:
IE₁ Atomic Number (Z) → Li Be B C N O F Ne The Great IE₁ Exceptions 1. Nitrogen (N) > Oxygen (O): ↑↑↑ N (2p³): Exactly Half-Filled (Stable!) ↑↓↑↑ O (2p⁴): e⁻ repulsion makes it easier to lose. 2. Beryllium (Be) > Boron (B): Be is 2s². 2s is highly penetrating (closer to nucleus) than 2p¹. Harder to remove 2s e⁻! Successive Ionization Energies (Identifying Valency) General Rule: IE₁ < IE₂ < IE₃ ≪ IE₄ (for Aluminum) 577 IE₁ 1816 IE₂ 2744 IE₃ 11577! IE₄ HUGE jump between IE₃ and IE₄ means the 4th electron is removed from a stable noble gas core. Conclusion: The element has exactly 3 valence electrons (Group 13)! 1. Halogen EA Trap (Cl > F) Expected: F > Cl. Actual: Cl > F ! F Tiny 2p shell. High e⁻-e⁻ repulsion! Cl Large 3p shell. Easily accepts e⁻. Electron Affinity Facts • Highest EA in Periodic Table = Chlorine (Cl) • Group 16 Exception (S > O): Just like F, Oxygen is too small. Oxygen actually has the LOWEST EA in Group 16! • Noble Gases & Be, Mg, N have POSITIVE EA. (Energy must be supplied to force an electron in). Electronegativity (EN) Scales & Diagonal Relationships Mulliken Scale EN = ( IE + EA ) / 2 Where IE and EA are in eV/atom. Pauling EN ≈ Mulliken EN / 2.8 Diagonal Relationships Li and Mg, Be and Al, B and Si behave similarly. Li Be B Mg Al Si Why? Moving right increases polarizing power (Zeff ↑). Moving down decreases it (r ↑). Diagonals cancel out!
Highest Electronegativity
Fluorine (4.0)
Followed by Oxygen (3.5) & N/Cl (3.0)
Highest Ionization Energy
Helium (He)
Noble gas, 1s² is closest to nucleus.
Highest Electron Affinity
Chlorine (Cl)
Fluorine suffers from e⁻ repulsion.
Lowest Ionization Energy
Cesium (Cs)
Best element for Photoelectric effect.
🔥 High-Yield JEE Exception: Second Electron Affinity is ALWAYS Endothermic!
While the first electron affinity (EA₁) of Oxygen is exothermic (Energy is released to form O⁻), the second electron affinity (EA₂) to form O²⁻ is highly Endothermic. You must force a negative electron into an already negative O⁻ ion, requiring substantial external energy to overcome electrostatic repulsion!
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