MATTER AND ITS STATES:
  Solid: fixed shape, volume | Liquid: fixed volume, shape of container
  Gas: no fixed shape/volume | Plasma: ionised gas (stars, lightning, neon signs)
  
  Changes of state (with heat): Solid → Liquid (melting) → Gas (vaporization)
  Reverse (with cooling): Gas → Liquid (condensation) → Solid (freezing)
  Sublimation: solid directly to gas (dry ice, iodine, camphor, naphthalene)
  
  Latent heat: heat absorbed/released during state change (no temperature change)

ATOMS AND MOLECULES:
  Law of Conservation of Mass: mass of reactants = mass of products
  Law of Definite Proportions: compound has fixed mass ratio of elements
  Mole concept: 1 mole = 6.022 × 10²³ particles
  Molar mass = mass of 1 mole = molecular weight in grams

PERIODIC TABLE (first 20 elements — must know):
  H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca
  Valency: group 1=1, group 2=2, group 13=3, group 14=4, group 15=3, group 16=2, group 17=1

CHEMICAL BONDING BASICS:
  Ionic bond: metal loses electrons → cation | non-metal gains → anion
    NaCl: Na loses 1e⁻ → Na⁺ | Cl gains 1e⁻ → Cl⁻
  Covalent bond: non-metals share electrons
    H₂O: O shares 2 pairs | CO₂: C shares 2 pairs with each O (double bonds)

MOTION:
  Distance: total path length (scalar)
  Displacement: shortest distance, direction matters (vector)
  Speed = distance/time (scalar) | Velocity = displacement/time (vector)
  Acceleration = change in velocity / time | a = (v-u)/t
  
  Equations of motion:
    v = u + at
    s = ut + ½at²
    v² = u² + 2as

FORCE:
  Newton's 1st Law: object at rest stays at rest unless net force acts
  Newton's 2nd Law: F = ma (force = mass × acceleration)
  Newton's 3rd Law: for every action, equal and opposite reaction
  
  Gravity: g = 9.8 m/s² (downward on Earth's surface)
  Weight W = mg | Mass = same everywhere | Weight = varies by location

WORK AND ENERGY:
  Work W = F × d × cosθ (θ = angle between force and displacement)
  Kinetic Energy: KE = ½mv²
  Potential Energy (gravitational): PE = mgh
  Law of Conservation of Energy: total mechanical energy constant (no friction)

ELECTRICITY:
  Electric current I = Q/t (coulombs per second = Ampere)
  Ohm's Law: V = IR (Voltage = Current × Resistance)
  Power: P = VI = I²R = V²/R (Watts)
  Series: same current, resistances add: R_total = R₁ + R₂ + R₃
  Parallel: same voltage, conductances add: 1/R = 1/R₁ + 1/R₂ + 1/R₃