Structure of the Atom
Madhya Pradesh Board · Class 9 · Science
Quick revision notes for Structure of the Atom — Madhya Pradesh Board Class 9 Science. Key concepts, formulas, and definitions for last-minute revision.
Key Topics to Revise
Discovery of Sub-atomic Particles
- Atoms are not indivisible but contain smaller particles called sub-atomic particles
- Three main sub-atomic particles: electrons, protons, and neutrons
- J.J. Thomson discovered electrons in 1897 using cathode ray tube experiments
Atomic Models
- Thomson's Model (1904): 'Plum pudding' or 'watermelon' model - electrons embedded in positive sphere
- Rutherford's Model (1911): Nuclear model with electrons revolving around nucleus
- Rutherford's alpha particle scattering experiment revealed the nucleus
Electronic Configuration and Bohr-Bury Rules
- Electrons are arranged in shells or energy levels around the nucleus
- Shells are designated as K, L, M, N or n = 1, 2, 3, 4
- Maximum electrons in shell = 2n² where n is shell number
Valency
- Valency is the combining capacity of an atom
- Determined by the number of valence electrons
- Atoms tend to achieve stable electronic configuration (octet in outermost shell)
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