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Structure of Atom cheat sheet
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NEET · Chemistry
Cheat sheet
Class 11 · Chapter 2Structure of Atom
Aufbau, Pauli, Hund — fill low energy first, two opposite spins, singly before pairing.
1. Discoveries
| Particle | Discovered by | Charge |
|---|---|---|
| Electron | J.J. Thomson (cathode rays) | −1.6 × 10⁻¹⁹ C |
| Proton | Goldstein (canal rays) | +1.6 × 10⁻¹⁹ C |
| Neutron | Chadwick | 0 |
Rutherford's α-scattering: tiny dense positive nucleus.
2. Bohr Model (H-like)
Spectral lines: , .
Lyman (n₁=1, UV), Balmer (2, visible), Paschen (3), Brackett (4), Pfund (5).
3. Quantum Ideas
Photoelectric effect: electrons are emitted only above threshold frequency; KE = hν − hν₀.
4. Quantum Numbers
| Number | Values | Tells |
|---|---|---|
| n (principal) | 1, 2, 3… | shell, size, energy |
| l (azimuthal) | 0 to n − 1 | subshell shape (s, p, d, f) |
| mₗ (magnetic) | −l to +l | orientation |
| mₛ (spin) | +½, −½ | spin |
5. Filling Orbitals
Order (n + l rule): 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p…
Exceptions: Cr = [Ar] 3d⁵ 4s¹, Cu = [Ar] 3d¹⁰ 4s¹ — half-filled / filled d is extra stable.
6. Key Points
- Nodes: radial = n − l − 1, angular = l.
- Max electrons in a shell = 2n².
- Isotopes: same Z; isobars: same A.
- Orbital holds max 2 electrons.
Remember: Bohr energy & radius | 4 quantum numbers | Aufbau, Pauli, Hund
Structure of Atom: questions and notes
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