Lesson Plan: Structure of Atom

Physical Chemistry

Structure of Atom

A journey from classical particles to the quantum mechanical model. This chapter explains why elements behave the way they do. It is highly conceptual but requires strong calculation skills for Bohr's Model and Quantum numbers.

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⚠️ Prerequisites

Basic Physics: Charge interactions (+ repels +), Kinetic Energy ($1/2 mv^2$), Centrifugal force.
Mole Concept: Molar mass and Avogadro's number.
Waves: Frequency ($\nu$), Wavelength ($\lambda$), and Velocity ($c$).

🧠 Study Approach

Dual Approach:
1. Formulas: Memorize Bohr's radius/energy formulas and Rydberg's formula perfectly.
2. Visualization: You must visualize the shape of orbitals (s, p, d) and how electrons fill them.

Study Sequence

1. Discovery of Subatomic Particles

Cathode Rays ($e^-$), Anode Rays ($p^+$), and Neutron ($n$). Charge-to-mass ratio ($e/m$).

2. Early Atomic Models

Thomson's Model (Plum Pudding). Rutherford's Gold Foil Experiment (Crucial): Discovery of Nucleus and its drawbacks.

3. Nature of Electromagnetic Radiation

Wave Nature: $c = \nu \lambda$.
Particle Nature: Planck's Quantum Theory ($E=h\nu$) and the Photoelectric Effect (Threshold frequency, work function).

4. Atomic Spectra (Hydrogen)

Emission vs Absorption spectra. The spectral series: Lyman (UV), Balmer (Visible), Paschen, Brackett, Pfund (IR). Using the Rydberg Formula.

5. Bohr's Model (CRITICAL)

Postulates. Quantization of angular momentum ($mvr = nh/2\pi$). Derivations of Radius, Velocity, and Energy of $n^{th}$ orbit. Limitations (Zeeman/Stark effect).

6. Towards Quantum Mechanics

Dual Behavior of Matter (de Broglie equation). Heisenberg's Uncertainty Principle (Fundamental limit of measurement).

7. Quantum Mechanical Model & Numbers

Concept of Orbital vs Orbit. The 4 Quantum Numbers: Principal ($n$), Azimuthal ($l$), Magnetic ($m_l$), Spin ($s$). Valid vs Invalid sets of numbers.

8. Shapes of Orbitals & Electronic Config

Shapes of s, p, d orbitals. Concept of Nodes (Radial/Angular).
Filling Rules: Aufbau Principle (n+l rule), Pauli Exclusion Principle, Hund's Rule. Exceptions: Cr (24) and Cu (29).

🎯 How to Practice

Calculations: Practice 15+ problems specifically on Bohr's Energy/Radius and the Hydrogen Spectrum. Watch out for units (eV vs Joules).

Quantum Logic: Practice determining if a set of Quantum Numbers is valid. (e.g., Can $n=3, l=3$? No, because $l$ must be less than $n$).

Configuration: Write the electronic configuration for atomic numbers 1 to 30 repeatedly until you memorize the exceptions (Cr, Cu).

📝 Quick Revision Formulas

Photoelectric Effect $$h\nu = h\nu_0 + \frac{1}{2}m_ev^2$$

Bohr's Model (Hydrogen-like) $$r_n = 0.529 \frac{n^2}{Z} \mathring{A}$$ $$E_n = -13.6 \frac{Z^2}{n^2} \text{ eV/atom}$$

Rydberg Formula $$\frac{1}{\lambda} = R_H Z^2 \left(\frac{1}{n_1^2} - \frac{1}{n_2^2}\right)$$

Nodes & Momentum $$\text{Radial Nodes} = n - l - 1$$ $$\text{Orbital Ang. Mom.} = \sqrt{l(l+1)}\frac{h}{2\pi}$$

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