Cheat sheet · NEET Preparation Chemistry
Classification of Elements and Periodicity in Properties cheat sheet
The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.
NEET · Chemistry
Cheat sheet
Class 11 · Chapter 3Classification of Elements and Periodicity in Properties
Across a period: size ↓, IE ↑, EN ↑. Down a group: size ↑, IE ↓, EN ↓.
1. History
- Döbereiner's triads; Newlands' law of octaves.
- Mendeleev: properties are periodic functions of atomic mass; left gaps (eka-aluminium = Ga).
- Modern periodic law (Moseley): properties are periodic functions of atomic number.
2. Blocks
| Block | Groups | Outer configuration |
|---|---|---|
| s | 1–2 | ns¹⁻² |
| p | 13–18 | ns² np¹⁻⁶ |
| d | 3–12 | (n−1)d¹⁻¹⁰ ns⁰⁻² |
| f | lanthanoids, actinoids | (n−2)f¹⁻¹⁴ |
3. Periodic Trends
| Property | Across a period → | Down a group ↓ |
|---|---|---|
| Atomic radius | decreases | increases |
| Ionisation enthalpy | increases | decreases |
| Electron gain enthalpy | more negative | less negative |
| Electronegativity | increases | decreases |
| Metallic character | decreases | increases |
4. Exceptions
- IE: N > O and Be > B (half-filled / filled subshell stability).
- Electron gain: Cl more negative than F (small size of F, electron repulsion).
- Cation smaller than its atom; anion larger.
5. Key Points
- Most electronegative: F (4.0).
- Noble gases: large positive Δ_eg H.
- Isoelectronic species: more Z ⇒ smaller size.
- Valence = group-based oxidation state.
Remember: Modern periodic law | s p d f blocks | trends + exceptions
Classification of Elements and Periodicity in Properties: questions and notes
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