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Chemistry: Fundamental Concepts, Reactions, and Stoichiometry

Chemistry studies the composition, structure, properties, and transformations of matter. It connects physics with biology and underlies medicine, materials science, energy technology, and environmental science. This chapter covers essential chemistry concepts for CBSE examinations.

Classification of matter: elements (pure, one atom type), compounds (elements chemically combined in fixed proportions), mixtures (physically combined, separable by physical methods). The mole concept: 1 mole = 6.022x10^23 particles (Avogadro's number). n = mass/molar mass. Stoichiometry uses mole ratios from balanced equations to calculate amounts of reactants and products. The limiting reagent is the reactant consumed first, determining the maximum product.

Atomic structure: Dalton's theory, subatomic particles (e-, p+, n), Bohr model (energy levels), quantum mechanical model (orbitals, quantum numbers n,l,ml,ms). The periodic table organises elements by atomic number. Periodic trends: atomic radius decreases across a period, increases down a group. Ionisation energy and electronegativity show opposite trends. Chemical bonding: ionic (electron transfer, metal+nonmetal), covalent (electron sharing, nonmetals), metallic. VSEPR theory predicts molecular shapes (linear, trigonal planar, tetrahedral, etc.). Hybridisation: sp (linear), sp2 (trigonal planar), sp3 (tetrahedral).

Types of reactions: combination, decomposition, displacement, double displacement, combustion, redox (OIL RIG — Oxidation Is Loss, Reduction Is Gain). Thermodynamics: first law (deltaU = q+w), enthalpy H = U+PV, exothermic (negative deltaH) and endothermic (positive deltaH) reactions, Hess's law, entropy, Gibbs free energy deltaG = deltaH - TdeltaS. Equilibrium: Kc, Le Chatelier's principle (equilibrium shifts to counteract changes). pH = -log[H+]. Organic chemistry: carbon tetravalency, functional groups (-OH, -CHO, -COOH), homologous series, isomerism, reactions (substitution, addition, esterification).

• Mole: n = mass/molar mass, 1 mole = 6.022e23 particles. Stoichiometry: balanced equation mole ratios. Limiting reagent determines yield.
• Atomic structure: quantum numbers n,l,ml,ms. Electron config: Aufbau, Pauli, Hund. Periodic trends: radius, IE, electronegativity.
• Bonding: ionic (electron transfer), covalent (sharing). VSEPR shapes. Hybridisation: sp, sp2, sp3. Octet rule exceptions.
• Redox: OIL RIG. Thermodynamics: deltaG = deltaH - TdeltaS; deltaG<0 means spontaneous. Equilibrium: Kc, Le Chatelier.
• Organic: functional groups, homologous series, isomerism, substitution/addition/esterification reactions. pH = -log[H+].