Title: 9th Class Chemistry Notes – Chapter 2: Structure of Atom

9th Class Chemistry
Chapter 2: Structure of Atom



Structure of Atom:



1. Subatomic Particles:

- Electron: Negatively charged particle, discovered by J.J. Thomson.

- Proton: Positively charged particle, discovered by Goldstein.

- Neutron: Neutral particle, discovered by James Chadwick.



2. Models of Atom:

- Thomson's Model: Plum pudding model.

- Rutherford's Model: Gold foil experiment, nucleus concept.

- Bohr's Model: Electrons revolve in fixed orbits.



3. Atomic Number and Mass Number:

- Atomic Number (Z): Number of protons in an atom.

- Mass Number (A): Number of protons + neutrons.



4. Isotopes and Isobars:

- Isotopes: Atoms with same atomic number but different mass numbers (e.g., Carbon-12 and Carbon-14).

- Isobars: Atoms with same mass number but different atomic numbers.



5. Electronic Configuration:

- Arrangement of electrons in shells.

- K, L, M shells etc. (2, 8, 18 rule).