CHEMCA
EXAM MASTER REVIEW SHEET
Periodic Classification of Elements
Strategic Summary for JEE Main, Advanced & NEET
1. Modern Periodic Law & Moseley's Experiment
The physical and chemical properties of the elements are periodic functions of their atomic numbers.
Moseley's Equation:
\[ \sqrt{\nu} = a(Z - b) \]
\(\nu\) = Frequency of X-rays, \(Z\) = Atomic Number, \(a, b\) = Constants
2. Effective Nuclear Charge (\(Z_{eff}\))
The Governing Equation:
\[ Z_{eff} = Z - \sigma \]
\(\sigma\) = Screening/Shielding constant (Calculated via Slater's Rules)
Shielding Power Order:
s > p > d > f
Trend:
Across a period: Increases (by 0.65 units)
Down a group: Remains constant (approx.)
3. Periodic Trends Summary
| Property | Across a Period (\(\to\)) | Down a Group (\(\downarrow\)) |
|---|---|---|
| Atomic Radius | Decreases | Increases |
| Ionization Enthalpy (IE) | Increases | Decreases |
| Electron Gain Enthalpy (\(\Delta_{eg}H\)) | More Negative | Less Negative |
| Electronegativity (EN) | Increases | Decreases |
| Metallic Character | Decreases | Increases |
4. Electronegativity Scales
Pauling Scale:
\[ X_A - X_B = 0.102 \sqrt{\Delta_{AB}} \]
\(\Delta\) in kJ/mol. \(X_{Fluorine} = 4.0\)
Mulliken Scale:
\[ X_M = \frac{IE + EA}{2} \]
Relation: \(X_P \approx \frac{X_M}{2.8}\)
5. Chemical Properties & Oxides
Basic Oxides
Metals (Left side)
\(Na_2O, MgO, CaO\)
Acidic Oxides
Non-metals (Right side)
\(Cl_2O_7, SO_3, P_4O_{10}\)
Amphoteric
Mnemonic: Janabe Ali...
\(ZnO, Al_2O_3, SnO, PbO, BeO\)
Neutral Oxides: \(CO, NO, N_2O, H_2O\) (Very important for NEET/JEE)
Diagonal Relationship: Similarities between 2nd period elements and 3rd period elements (diagonally opposite).
Pairs: \((Li, Mg)\), \((Be, Al)\), \((B, Si)\). Cause: Similar ionic potential (\(\phi = Charge/Radius\)).
Pairs: \((Li, Mg)\), \((Be, Al)\), \((B, Si)\). Cause: Similar ionic potential (\(\phi = Charge/Radius\)).
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