Скачать или смотреть Rutherford’s Atomic Model | Atoms | CBSE Class 12 Physics by Elearnin

Welcome to Elearnin, In this 3d animated videos we will teach you about Rutherford’s Atomic model from the Class 12 Chemistry - CBSE – NCERT by Elearnin

In this video you will learn about Rutherford’s Atomic Model
• Rutherford’s Solar System Model
• Alpha Ray Scattering Experiment
• Postulates of the Alpha Ray Scattering Experiment
• Size of the Nucleus
• Distance of Closest Approach
• Alpha Particle Trajectory
• Drawbacks of Rutherford’s Model

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Rutherford’s Solar System Model:
In the same way how planets revolve around the sun, electrons revolve around nuclei in an atom. The nucleus contains a positive charge while the electrons contain a negative charge. As a result, the atom is constant. As the revolution of the electrons around the nucleus is compared to the revolution of the planets around the sun, the model is called Rutherford’s Solar System Model.

Alpha Ray Scattering Experiment:

In this, alpha rays emanating from a radioactive material were concentrated onto a thin foil. Few of them passes straight through the foil. Others were bent at various angles. These alpha particles once bent illuminated a fluorescent screen. Few atoms returned at the exact same angle. The reason behind this was the electro positivity of the alpha particles. As they neared the centre of the atom in the gold foil, they were repelled and sent backwards. In reality, alpha particles are electropositive. If the alpha particle is being repelled and sent back, it means that the centre of the atom is electropositive. Therefore, it was found that the nucleus is electropositive.

Postulates of the Alpha Ray Scattering Experiment:

Majority of the atomic mass is concentrated in the centre of the nucleus in a very small part. This is the nucleus. The nucleus is electropositive. Its size is 10-13ms. There are equivalent electrons around the nucleus to neutralise the atom. They don’t fall into the nucleus as a result of the forces of attraction due to the fact that they revolve around the atom similar to the solar system.

Size of the Nucleus:
The size of the nucleus is between 10-15 to 10-14 m. The atomic radius is 10-10m.

Distance of Closest Approach:
In the Rutherford Gold Foil Experiment, alpha particles emanating from a radioactive source are dispersed in all angles by the gold foil. The particles hitting the nucleus are sent back based on the principle of ‘Like forces repel each other’. However few alpha particles that come close to the nucleus are dispersed at various angles. Few of them are deflected very close to the nucleus. The closest the alpha particle can come to a nucleus is the Impact Parameter.

Alpha Particle Trajectory:
The trajectory traced by an alpha particle depends on the impact parameter of collision between the particle and the nucleus. The impact parameter is the perpendicular distance of the initial velocity vector of the a-particle from the centre of the nucleus. A given beam of alpha particles has a distribution of impact parameters, so that the beam is scattered in various directions with different probabilities. The alpha particle closest to the nucleus suffers the largest scattering. In case of head-on collision, the impact parameter is minimum and the a-particle rebounds back. For a large impact parameter, the alpha particle goes nearly undeviated and has a small deflection. The fact that only a small fraction of the number of incident particles rebound back indicates that the number of a-particles undergoing head on collision is small. This, in turn, implies that the mass and positive charge of the atom is concentrated in a small volume. Rutherford scattering therefore determines an upper limit to the size of the nucleus.

Drawbacks of Rutherford’s Model:
Rutherford’s model states that electrons revolve around the nucleus. However, based on the dielectric principle, revolving electrons must emit large amounts of energy. If this happens however, they would lose energy and their orbits would reduce leading the electrons to spiral into the nucleus resulting in the collapse of the atom. However, this doesn’t occur and the atom remains stable. Therefore, Rutherford’s model doesn’t explain the stability of the atom. It doesn’t explain how the revolving electrons stay in orbit. It doesn’t explain the distribution of electrons in the atom.


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