Atomic Structure
The concept of atoms as fundamental building blocks of matter dates back to early Indian and Greek philosophers (approx. 400 B.C.), famously termed "a-tomio" (uncuttable). However, modern atomic theory began in the 19th century.
Discovery of Subatomic Particles
| Particle | Scientist | Year | Experiment | Key Outcome |
|---|---|---|---|---|
| Electron | J. J. Thomson | 1897 | Cathode Ray Tube | Negatively charged particle |
| Proton | Eugen Goldstein | 1886 | Canal Ray | Positively charged particles |
| Neutron | James Chadwick | 1932 | Alpha on Beryllium | Neutral particle in nucleus |
Particle Characteristics
| Property | Electron (e⁻) | Proton (p⁺) | Neutron (n⁰) |
|---|---|---|---|
| Charge | −1.6 × 10⁻¹⁹ C | +1.6 × 10⁻¹⁹ C | 0 |
| Relative Charge | -1 | +1 | 0 |
| Mass (kg) | 9.11 × 10⁻³¹ | 1.67 × 10⁻²⁷ | 1.67 × 10⁻²⁷ |
| Relative Mass | 1/1836 | 1 | ≈1 |
| Location | Outside nucleus | Inside nucleus | Inside nucleus |
Atomic Models Evolution
| Model | Scientist | Concept | Limitation |
|---|---|---|---|
| Plum Pudding | Thomson (1904) | Sphere of positive charge with embedded electrons | Failed to explain alpha scattering |
| Nuclear Model | Rutherford (1911) | Small dense nucleus, mostly empty space | Could not explain stability |
| Bohr’s Model | Bohr (1913) | Fixed energy orbits (K, L, M) | Failed for multi-electron atoms |
Quantum Mechanical Model Features
| Feature | Explanation |
|---|---|
| Dual Nature | Electrons have both particle and wave nature (de Broglie) |
| Uncertainty Principle | Impossible to know exact position & momentum simultaneously (Heisenberg) |
| Wave Function (ψ) | Describes electron behavior; obtained from Schrödinger equation |
| ψ² | Probability of finding electron in a region (orbital) |
| Orbitals | 3D space with high probability of finding electrons |
| Quantization | Only specific discrete energy levels allowed |
| Quantum Numbers | n, l, mₗ, mₛ describe unique state of electron |
Electromagnetic Radiation & Quantum Theory
| Concept | Key Points |
|---|---|
| EM Radiation | Oscillating electric/magnetic fields. Speed of light (c). c = λν |
| Planck’s Theory | Energy emitted/absorbed in packets (Quanta). E = hν |
| de Broglie | Matter waves. λ = h / mv |
| Heisenberg Uncertainty | Δx · Δp ≥ h / 4π. Rules out fixed orbits. |
Key Principles
Aufbau Principle
Electrons fill lowest energy orbitals first.
Pauli Exclusion
No two electrons can have the same 4 quantum numbers.
Hund’s Rule
Pairing starts only after each orbital in a subshell is singly occupied.
Heisenberg Uncertainty
Δx · Δp ≥ h / 4π
Important Formulas
Planck's Equation: E = hν (h = 6.626 × 10⁻³⁴ J·s)
de Broglie Relation: λ = h / mv
Equilibrium
Equilibrium is the state of balance where the rate of the forward reaction equals the rate of the backward reaction. It is dynamic, meaning reactions continue but concentrations remain constant.
Le Chatelier’s Principle
"When a system at equilibrium is disturbed, it shifts to counteract the disturbance."
Increase Reactant → Shifts Forward
Increase Product → Shifts Backward
Increase Pressure → Shifts to fewer moles side
Decrease Pressure → Shifts to more moles side
Exothermic: Heat is product. Inc Temp → Backward.
Endothermic: Heat is reactant. Inc Temp → Forward.
Equilibrium Constants
- Kc: Using molar concentrations.
- Kp: Using partial pressures (gases).
- Relation: Kp = Kc(RT)^Δn
Calculating Kc
Chemical Kinetics
Chemical kinetics deals with the rate of reaction and factors affecting it.
Rate of Reaction
Change in concentration per unit time.
Rate = -Δ[Reactants]/Δt = +Δ[Products]/ΔtFactors Affecting Rate
- Concentration
- Temperature
- Catalyst
- Surface Area
Electrochemistry
Study of electricity and chemical reactions. Key concepts include Electrochemical Cells, Nernst Equation, and Conductance.
Types of Cells
| Feature | Galvanic Cell | Electrolytic Cell |
|---|---|---|
| Reaction | Spontaneous | Non-spontaneous |
| Energy Conversion | Chemical → Electrical | Electrical → Chemical |
| Anode Charge | Negative (-) | Positive (+) |
| Cathode Charge | Positive (+) | Negative (-) |
Nernst Equation
Calculates EMF at non-standard conditions.
Faraday's Laws
1st Law: m = ZQ (Mass ∝ Charge)
2nd Law: Mass ∝ Equivalent Weight
Numericals
EMF Calculation
Nernst Equation Application
Faraday's 1st Law
Stoichiometry & Redox
Core Concepts
Redox Titrations
Use the normality equation: N₁V₁ = N₂V₂
Titration Calculation (KMnO₄ vs FeSO₄)
Stoichiometry: Mass-Mass
Exam Tip: Equivalent Weight
Always remember n-factors for Redox:
• KMnO₄ (Acidic) n = 5
• K₂Cr₂O₇ (Acidic) n = 6
• Oxalic Acid n = 2