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Title: Atomic Theory and Models Timeline

Description: Welcome to the world of discoveries. As we go on to the legendary discoveries of Atomic Theory and its models of certain Scientist who contributed accordingly. Let us go back in time and explore the world of Atomic Theory.

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Name of Atomic Model: Atomos / Sphere

Date: 430 bce

Description: This fundamental or basic unit was what Democritus called an atom. He called this the theory of the universe: All matter consists of atoms, which are bits of matter too small to be seen.

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Name of Atomic Model: the billiard ball model

Date: 1808

Description: Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass.

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Name of Atomic Model: the plum pudding model

Date: 1897

Description: Thomson discovered the first subatomic particle, the electron, while researching cathode rays. To explain the neutrality of atoms, Thomson proposed a model of the atom in which negative electrons are scattered throughout a sphere of positive charge. He called his atom the plum pudding model.

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Name of Atomic Model: Rutherford nuclear atom

Date: 1911

Description: The Rutherford atomic model was also known as the "Rutherford nuclear atom" and the "Rutherford Planetary Model". In 1911, Rutherford described the atom as having a tiny, dense, and positively charged core called the nucleus. Rutherford established that the mass of the atom is concentrated in its nucleus.

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Name of Atomic Model: Rutherford-Bohr Model

Date:  1913

Description: The Bohr Model has an atom consisting of a small, positively charged nucleus orbited by negatively charged electrons. Unlike earlier models, the Bohr Model explains the Rydberg formula for the spectral emission lines of atomic hydrogen.

Main Points of the Bohr Model

Electrons orbit the nucleus in orbits that have a set size and energy.

The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit.

Radiation is absorbed or emitted when an electron moves from one orbit to another.

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Name of Atomic Model:  Quantum Mechanical model

Date: 1926

Description: The Schrödinger model assumes that the electron is a wave and tries to describe the regions in space, or orbitals, where electrons are most likely to be found.

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Name of Atomic Model: Cloud model

Date: 1932

Description: Chadwick is responsible for discovering the existence of the neutron, the neutral particle that shares the nucleus with the positively charged proton. Chadwick's discovery forced a revision of the cloud model, and scientists sometimes refer to the revised version as the James Chadwick atomic model.