02/08/2025
ATOMIC MODEL THROUGH HISTORY
1. John Dalton’s Model (1803) – Solid Sphere Model
Overview:
Dalton proposed that all matter is made up of indivisible particles called atoms.
He imagined atoms as tiny, solid spheres—like billiard balls.
Key Ideas:
Atoms of the same element are identical in mass and properties.
Atoms cannot be created, divided, or destroyed.
Compounds form when atoms of different elements combine in fixed ratios.
Importance:
First scientific model of the atom based on experimental evidence (like gas laws).
Laid the groundwork for modern chemistry.
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2. J.J. Thomson’s Model (1904) – Plum Pudding Model
Overview:
After discovering the electron, Thomson proposed that atoms are made of a positively charged substance with negatively charged electrons scattered within it—like raisins in pudding.
Key Ideas:
Atoms are divisible.
Electrons are negatively charged subatomic particles.
The rest of the atom is a blob of positive charge to balance the electrons.
Importance:
First model to show that atoms have internal structure.
Introduced the idea of subatomic particles.
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3. Ernest Rutherford’s Model (1911) – Nuclear Model
Overview:
Conducted the gold foil experiment where alpha particles were fired at a thin sheet of gold.
Most passed through, but some were deflected at large angles.
Key Ideas:
Atoms are mostly empty space.
A small, dense, positively charged nucleus is at the center.
Electrons orbit around this nucleus.
Importance:
Disproved the plum pudding model.
Introduced the concept of a nucleus.
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4. Niels Bohr’s Model (1913) – Planetary Model
Overview:
Bohr expanded on Rutherford’s model using discoveries from quantum theory.
Key Ideas:
Electrons orbit the nucleus in fixed paths or “energy levels.”
Each level has a specific amount of energy.
Electrons can jump to higher levels when energy is absorbed and fall back down when energy is released (as light).
Importance:
Explained why atoms emit light in specific c
