𝐀𝐥𝐥 𝐬𝐜𝐢𝐞𝐧𝐜𝐞 𝐍𝐨𝐭𝐞 & 𝐌𝐂𝐐𝐬 9 𝐭𝐨 𝐁.𝐬

Normal human body parameter (adults)

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Plant Cell

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Evolution of Atomic Models ⚛️

1. John Dalton — Solid Sphere Model (1803)
“Atoms are tiny, indivisible solid particles that combine in fixed ratios to form matter.”
Explanation:
➡️Dalton proposed the first scientific atomic theory.
➡️According to him, atoms were like hard solid balls.
➡️Atoms of the same element are identical, while different elements have different atoms.
➡️Chemical reactions involve rearrangement of atoms, not creation or destruction.

2. J. J. Thomson — Plum Pudding Model (1904)
“Negative electrons are embedded inside a positively charged sphere.”
Explanation:
➡️Thomson discovered the electron using cathode ray experiments.
➡️He suggested that atoms are made of a positive sphere with electrons scattered inside it.
➡️This model is called the Plum Pudding Model because electrons resembled raisins inside pudding.

3. Ernest Rutherford — Nuclear Model (1911)
“Atoms contain a tiny, dense, positively charged nucleus with electrons revolving around it.”
Explanation:
➡️Rutherford performed the famous Gold Foil Experiment.
➡️He discovered that most of the atom is empty space.
➡️The positive charge and most mass are concentrated in the nucleus.
➡️Electrons revolve around the nucleus like planets around the Sun.

4. Niels Bohr — Bohr’s Planetary Model (1913)
“Electrons move in fixed energy levels or shells around the nucleus.”
Explanation:
➡️Bohr improved Rutherford’s model.
➡️He proposed that electrons revolve in specific circular orbits called energy levels.
➡️Electrons can jump between levels by absorbing or releasing energy.
➡️This model explained the spectrum of hydrogen atom.

5. Erwin Schrödinger — Quantum Mechanical Model (1926)
“Electrons exist in probability clouds rather than fixed paths.”
Explanation:
➡️Schrödinger developed the wave equation for electrons.
➡️Electrons do not move in fixed orbits.
➡️Their exact position cannot be determined; instead, we predict the probability of finding them.
➡️This modern model is called the Electron Cloud Mod

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