Structure of atom: Rutherford atomic model anf Bohr atomic theory

Ratherford atomic model

In 1911 Rutherford performance experiment in order to know the arrangement of electron and proton in atom.

Rutherford experiment

Rutherford bombarded a very thin gold foil with alpha particles. The thickness of the gold foil was 0.0004 cm. Alpha particles are helium nuclie having double positive charge. He produced these particles from disintegration of polonium metal. During experiment, most of alpha particles passed through the foil without deflection. Only few of these Alpha particle was slightly deflected.

One in 1 million was reflected through an angle greater than 90 degree from their straight path ratherford perform a series of experiment using oil of other element also he observed similar result from is experiments.

Conclusions of Rutherford experiments:

1. Since majority of Alpha particle pass through file on deflected so most of space occupied by atom must be empty.

2. The deflection of a few Alpha particle through angles greater than 90 degree shows that these particles are reflected by electromagnetic repulsion between positive charge Alpha particles and the positive recharge part of atom.

3. Mersal Alpha particles are not deflected by electron.

Rutherford atomic model.

On the basis of conclusions of these experiments Rutherford perform proposed a new model of an atom. He proposed:

i. A planetary model ( a similar to solar system) for an atom

ii. An atom is the neutral particle.

iii. The mass of atom is concentrated in very small dense positivly charged region.

iv. Thiis region was named as a nucleus.

Electron revolve around the nucleus in circles.

These circles are called Orbits

The scientific force due to the revolution of electrons balances the electrostatic force of attraction between the nucleus and the electron.

Defects in Rutherford's atomic model.

Rutherford atomic model has following defects

I. Classical physics suggest that electron being charged particle will EMIT energy continuously while revolving around the nucleus does the orbit of revolving electron becomes smaller and smaller until it would fall into the nucleus this would collapse the atomic structure but it never happens.

2. If the revolving electrons emits energy continuously it should form a continuous spectrum for an atom but Alliance spectrum is obtaine

Bohr atomic theory

In order to remove defects from the Rutherford's atomic model, in 1913 Neil Bohr proposed a model for atom that was similar to Rutherford's Atomic model. This model explains the observed lines spectrum of hydrogen atom. The main points of Bohr atomic models are as follows.

1. The electron revolves around the nucleus in one of the circular arbits of an atom. Each Orbit has a fixed energy so each orbit is also called energy level.

2. The energy of the electron in an Orbit is proportional to its distance from the nucleus the further the electron is from the nucleus more it has.

3. Electron revolve only on those are bits for which the angular momentum of electron is an integral multiple of H2O where h is Planck's Constant its value is 6.6 to 6 times 34 is

4. Delight is absorbed when an electron jumps to a higher energy orbit and emitted when an electron Falls into pure lower energy Orbit electron present in a particular orbital does not EMIT or absorb energy.

The energy of the light emitted or absorbed s exactly equal to the difference between energies of orbit.

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