Ancient Theories:
1. Democritus (5th Century BCE) proposed that matter consists of indivisible particles called "atomos."
2. Aristotle rejected Democritus' theory and supported the idea of four fundamental elements: earth, water, air, and fire.
Modern Developments:
1. John Dalton (1803) proposed the atomic theory, suggesting atoms are indivisible and combine in fixed ratios to form compounds.
2. J.J. Thomson (1897) discovered the electron, leading to the "Plum Pudding Model."
3. Ernest Rutherford (1911) conducted the Gold Foil Experiment, discovering the atomic nucleus.
4. Niels Bohr (1913) introduced quantized orbits for electrons.
5. Quantum Mechanical Model (1920s) developed by Schrödinger and Heisenberg provided a probabilistic model of electron distribution.
⚡ Electron (e⁻): Discovered by J.J. Thomson using cathode ray tube experiment.
➕ Proton (p⁺): Discovered by E. Goldstein through anode rays.
🟢 Neutron(n⁰) : Discovered by James Chadwick in 1932.
🔵 Thomson's Model: Plum pudding model.
🎯 Rutherford's Model: Nuclear model based on gold foil experiment.
📢 Bohr's Model: Electrons move in fixed orbits around the nucleus.
Model Description: Also known as the "Plum Pudding Model".
Electrons are embedded in a positively charged "soup" like raisins in a pudding.
Gold Foil Experiment: Observed deflections when alpha particles passed through gold foil.
Conclusions:
1. Atoms have a dense, positively charged nucleus.
2. Electrons orbit the nucleus.
3. Most of the atom is empty space.
Postulates:
1. Electrons move in discrete orbits (energy levels).
2. Energy is absorbed/emitted when electrons jump between levels.
1st shell: Max 2 electrons.
2nd shell: Max 8 electrons.
3rd shell: Max 18 electrons.
Niels Bohr's Model (1913):
1. Electrons move in fixed orbits (shells) around the nucleus.
2. Energy levels are quantized, meaning electrons can only occupy specific orbits.
3. Electrons absorb or emit energy when transitioning between orbits.
Bohr-Bury Principle:
1. The maximum number of electrons in a shell follows the formula 2n² (where n = shell number).
2. The outermost shell can hold a maximum of 8 electrons (Octet Rule).
3. Electrons fill inner shells before moving to higher energy levels.
Number of electrons an atom gains, loses, or shares to form a stable compound.
Example: Sodium (Na) has valency 1, Oxygen (O) has valency 2.
Atomic Number (Z) = Number of protons.
Mass Number (A) = Protons + Neutrons.
📌 Isotopes: Atoms with same atomic number but different mass number (e.g., Carbon-12, Carbon-14).
🎠Isobars: Atoms with same mass number but different atomic numbers (e.g., Argon-40 & Calcium-40).
Definition: Isotones are atoms of different elements that have the same number of neutrons but different numbers of protons.
Examples:
1. Carbon-14 (6 protons, 8 neutrons) and Nitrogen-15 (7 protons, 8 neutrons).
2. Oxygen-16 (8 protons, 8 neutrons) and Fluorine-17 (9 protons, 8 neutrons).
Significance:
1. Helps in nuclear studies and radioactive decay analysis.
2. Useful in understanding nuclear reactions and stability of atoms.
Please don not use wrong word