Chemistry

Atomic Structure

Protons (+) in nucleus—Defines element (Z)

Neutrons (0) in nucleus—Adds to mass number (A)

Electrons (-) orbit nucleus—Determines chemistry

A = Z + N—Mass # = protons + neutrons

Isotopes: same Z, different N—

Ions: atom gains/loses electrons—

Electron config: 1s² 2s² 2p⁶...—Aufbau principle

Valence electrons: outermost shell—Determine bonding

Periodic Table Trends

Atomic radius ↑ down group—

Atomic radius ↓ across period—

Ionization energy ↓ down group—

Ionization energy ↑ across period—

Electronegativity ↓ down group—

Electronegativity ↑ across period—

Metallic character ↑ down group—

Metallic character ↓ across period—

Chemical Bonding

Ionic: metal + nonmetal—Transfer of electrons

Covalent: nonmetal + nonmetal—Sharing electrons

Metallic: metal + metal—Sea of electrons

Polar covalent: unequal sharing—ΔEN 0.4–1.7

Nonpolar covalent: equal sharing—ΔEN < 0.4

Hydrogen bond: H with N, O, F—Strong intermolecular

Van der Waals (London)—Weakest intermolecular

Dipole-dipole—Polar molecules attract

Reaction Types

Synthesis: A + B → AB—Combination

Decomposition: AB → A + B—Breaking apart

Single replacement: A + BC → AC + B—

Double replacement: AB + CD → AD + CB—

Combustion: CₓHₓ + O₂ → CO₂ + H₂O—

Oxidation: loss of electrons—OIL RIG

Reduction: gain of electrons—

Stoichiometry

Mole = 6.022×10²³ particles—Avogadro's number

Molar mass: g/mol from periodic table—

n = mass / molar mass—Moles calculation

Balance: same atoms each side—

Limiting reagent: runs out first—

% yield = (actual/theoretical)×100—

At STP: 1 mol gas = 22.4 L—

Acids, Bases & pH

pH = -log[H⁺]—

pOH = -log[OH⁻]—

pH + pOH = 14—At 25°C

pH < 7 → acidic—

pH = 7 → neutral—

pH > 7 → basic—

Strong acids: HCl, HNO₃, H₂SO₄—Fully dissociate

Strong bases: NaOH, KOH—Fully dissociate

Ka × Kb = Kw = 1×10⁻¹⁴—

Gas Laws

PV = nRT—Ideal gas law

R = 0.0821 L·atm/(mol·K)—Gas constant

R = 8.314 J/(mol·K)—SI gas constant

Boyle: P₁V₁ = P₂V₂—Const T, n

Charles: V₁/T₁ = V₂/T₂—Const P, n

Gay-Lussac: P₁/T₁ = P₂/T₂—Const V, n

Avogadro: V₁/n₁ = V₂/n₂—Const T, P

Dalton: P_total = P₁ + P₂ + ...—Partial pressures

STP: 0°C (273.15 K), 1 atm—

Equilibrium & Kinetics

K_eq = [products]/[reactants]—At equilibrium

K > 1 → products favored—

K < 1 → reactants favored—

Le Chatelier's principle—System opposes change

Rate = k[A]ᵐ[B]ⁿ—Rate law

↑ temp → ↑ rate—

↑ concentration → ↑ rate—

Catalyst lowers activation energy—

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