Class 9 Chemistry NCERT Notes
Chapter 1: Matter in Our Surroundings
States of Matter: Solid, Liquid, Gas
o Solid: Fixed shape & volume, particles vibrate, strong forces.
o Liquid: Fixed volume, no fixed shape, particles slide past each other.
o Gas: No fixed shape or volume, particles move freely, weak forces.
Characteristics:
o Diffusion: Gas particles mix due to random motion.
o Compressibility: Gas > Liquid > Solid.
Change of States: Melting, Freezing, Evaporation, Condensation, Sublimation.
Latent Heat: Energy required to change state without changing temperature.
Chapter 2: Is Matter Around Us Pure?
Pure Substance: Single type of particle (Element or Compound).
Mixture: Contains 2+ substances physically mixed.
o Homogeneous (solution) & Heterogeneous.
Separation Techniques:
o Filtration, Evaporation, Distillation, Chromatography, Sublimation.
Chapter 3: Atoms and Molecules
Atom: Smallest unit of an element.
Molecule: Smallest unit of a substance with properties.
Laws of Chemical Combination:
o Law of Conservation of Mass: Mass is neither created nor destroyed.
o Law of Definite Proportions: A compound always has the same ratio of
elements.
o Law of Multiple Proportions: Elements combine in simple ratios.
Atomic & Molecular Mass: Sum of atomic masses of constituent atoms.
Chemical Formula: Symbolic representation of composition.
Chapter 4: Structure of the Atom
Dalton’s Atomic Theory: Atoms indivisible, elements composed of same type of
atoms.
Discovery of Electron: J.J. Thomson; Electron = negative particle.
Rutherford Model: Nucleus (positive), electrons revolve around.
Bohr Model: Electrons in discrete energy levels.
Atomic Number (Z): Number of protons.
Mass Number (A): Protons + Neutrons.
Chapter 1: Matter in Our Surroundings
States of Matter: Solid, Liquid, Gas
o Solid: Fixed shape & volume, particles vibrate, strong forces.
o Liquid: Fixed volume, no fixed shape, particles slide past each other.
o Gas: No fixed shape or volume, particles move freely, weak forces.
Characteristics:
o Diffusion: Gas particles mix due to random motion.
o Compressibility: Gas > Liquid > Solid.
Change of States: Melting, Freezing, Evaporation, Condensation, Sublimation.
Latent Heat: Energy required to change state without changing temperature.
Chapter 2: Is Matter Around Us Pure?
Pure Substance: Single type of particle (Element or Compound).
Mixture: Contains 2+ substances physically mixed.
o Homogeneous (solution) & Heterogeneous.
Separation Techniques:
o Filtration, Evaporation, Distillation, Chromatography, Sublimation.
Chapter 3: Atoms and Molecules
Atom: Smallest unit of an element.
Molecule: Smallest unit of a substance with properties.
Laws of Chemical Combination:
o Law of Conservation of Mass: Mass is neither created nor destroyed.
o Law of Definite Proportions: A compound always has the same ratio of
elements.
o Law of Multiple Proportions: Elements combine in simple ratios.
Atomic & Molecular Mass: Sum of atomic masses of constituent atoms.
Chemical Formula: Symbolic representation of composition.
Chapter 4: Structure of the Atom
Dalton’s Atomic Theory: Atoms indivisible, elements composed of same type of
atoms.
Discovery of Electron: J.J. Thomson; Electron = negative particle.
Rutherford Model: Nucleus (positive), electrons revolve around.
Bohr Model: Electrons in discrete energy levels.
Atomic Number (Z): Number of protons.
Mass Number (A): Protons + Neutrons.
