Atoms and Molecules
CBSE · Class 9 · Science
Quick revision notes for Atoms and Molecules — CBSE Class 9 Science. Key concepts, formulas, and definitions for last-minute revision.
Key Topics to Revise
Historical Background and Laws of Chemical Combination
- Ancient Indian philosopher Maharishi Kanad (500 BC) proposed the concept of 'Parmanu' - smallest indivisible particles
- Greek philosophers Democritus and Leucippus called indivisible particles 'atoms' (meaning indivisible)
- Antoine Lavoisier established the foundation of chemical sciences through experimental work
Dalton's Atomic Theory
- John Dalton (1766-1844) provided the first scientific atomic theory
- Theory explained both laws of chemical combination through atomic concepts
- Six main postulates form the foundation of atomic theory
Atoms - Structure and Properties
- Atoms are extremely small - millions stacked would be as thick as paper
- Atomic radius measured in nanometers (1 nm = 10⁻⁹ m)
- Each element has unique symbols following IUPAC conventions
Molecules and Their Types
- Molecules are groups of two or more atoms bonded together
- Can be formed from same element atoms or different element atoms
- Atomicity refers to number of atoms in a molecule
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Sources & Official References
- NCERT Official — ncert.nic.in
- CBSE Academic — cbseacademic.nic.in
- CBSE Official — cbse.gov.in
- National Education Policy 2020 — education.gov.in
Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.
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