Chemistry forms a major part of the JEE syllabus, and mastering its basic concepts is essential for cracking the exam. This guide covers fundamental chemistry topics, from atomic structure to chemical equilibrium, providing a strong foundation for JEE aspirants. The concepts are explained with clarity and depth to help you build your understanding and problem-solving skills.
The atomic structure is the backbone of chemistry. It explains the arrangement of electrons, protons, and neutrons inside an atom and influences chemical behavior.
- Dalton's Atomic Theory: Atoms are indivisible, identical within an element, and combine in fixed ratios.
- Thomson's Plum Pudding Model: Atom is a positively charged sphere with embedded electrons.
- Rutherford Model: Atom has a dense, positively charged nucleus with electrons orbiting around.
- Bohr Model: Electrons orbit nucleus in fixed energy levels (shells) without radiating energy.
- Electrons exhibit wave-particle duality.
- Schrödinger’s wave equation describes electron probability distributions (orbitals).
- Quantum numbers (n, l, m_l, m_s) define electron states:
- Electrons fill orbitals according to Aufbau principle, Pauli exclusion principle, and Hund’s rule.
- Example: Oxygen electronic configuration: \(1s^2\,2s^2\,2p^4\).
Chemical bonding explains how atoms combine to form molecules and compounds. Understanding bonding helps predict molecule shape, polarity, and reactivity.
- Formed by transfer of electrons from metal to non-metal.
- Results in cations and anions attracted by electrostatic forces.
- Properties: high melting/boiling points, conduct electricity in molten/aqueous states.
- Formed by sharing electrons between two non-metals.
- Can be single, double, or triple bonds.
- Properties depend on bond polarity and molecule shape.
One atom donates both electrons to form a bond (common in complex ions).
Valence Shell Electron Pair Repulsion theory predicts molecular geometry based on repulsion between electron pairs.
Atomic orbitals mix to form hybrid orbitals explaining molecular shapes:
Describes bonding by combining atomic orbitals to form molecular orbitals (bonding and antibonding).
Matter exists in different states: solid, liquid, and gas. Understanding their properties is crucial for thermodynamics and kinetic theory.
- Gas particles move randomly with elastic collisions.
- Pressure arises from collisions on container walls.
- Average kinetic energy proportional to absolute temperature.
Real gases deviate from ideal behavior at high pressure and low temperature due to intermolecular forces and volume of particles.
- Liquids have definite volume but no fixed shape.
- Solids have definite shape and volume; particles vibrate around fixed positions.
- Types of solids: crystalline and amorphous.
Thermodynamics studies energy changes during chemical and physical processes.
Heat content at constant pressure. \(\Delta H\) indicates exothermic/endothermic reactions.
Measure of disorder/randomness.
Determines spontaneity: \( \Delta G = \Delta H - T \Delta S \).
If \( \Delta G < 0 \), process is spontaneous.
Total enthalpy change is sum of individual steps, regardless of reaction path.
At equilibrium, forward and backward reaction rates are equal; concentrations remain constant.
\(K_c = \frac{[Products]^{coefficients}}{[Reactants]^{coefficients}}\) for reactions in solution.
\(K_p\) for gases (partial pressures).
System shifts to counteract changes in concentration, pressure, or temperature.
Ionic equilibrium explains the dissociation of acids, bases, and salts in solution.
\(H_2O \leftrightarrow H^+ + OH^-\)
Ion product \(K_w = [H^+][OH^-] = 1 \times 10^{-14}\) at 25°C.
\[ \mathrm{pH} = -\log [H^+], \quad \mathrm{pOH} = -\log [OH^-], \quad \mathrm{pH} + \mathrm{pOH} = 14 \]
Resist change in pH on addition of small amounts of acid/base.
Study of reaction rates and factors influencing them.
Change in concentration of reactants/products per unit time.
Rate = \(k [A]^m [B]^n\), where \(m, n\) are reaction orders.
Order: sum of powers in rate law (experimentally determined).
Molecularity: number of molecules involved in elementary step.
Deals with phenomena at surfaces and interfaces.
Accumulation of molecules on solid surfaces.
Types: Physical (weak Van der Waals forces), Chemical (strong covalent bonds).
Catalysts speed up reactions without being consumed.
Mixtures with particle size between solutions and suspensions.
Examples: sols, gels, emulsions.
Review of element arrangement and trends: atomic radius, ionization energy, electron affinity, electronegativity, metallic character.
This guide provides a solid base for JEE Chemistry preparation. Deepen your understanding by solving past JEE problems, revisiting tough concepts, and staying consistent in practice.