Chapter 4: Structure of the Atom

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Structure of Atom


Compare all the proposed models of an atom given in this chapter.


Thomson’s Model of an Atom:

J.J Thomson gave the first model for the structure of an atom. According to his model, the atoms consist of a positively charged sphere in which the electrons are embedded in it like the Christmas pudding. The atom is electrically neutral because the number of negative charges is equal in magnitude with the number of positive charges.

Drawbacks of Thomson’s model of an atom:

It does not explain the stability of an atom. It does not explain the nucleus of an atom.

Rutherford’s Model of an Atom:

Rutherford performed the Gold foil experiment in which the fast-moving alpha particles were made fall on the gold foil. Some of the alpha particles deflect at higher angles while some deflect at smaller angles and some went undeflected.

According to Rutherford’s model, the atom contains a nucleus at the center which is heavy and positively charged. The size of the nucleus is very small as compared to the size of the atom. The electron is a negatively charged particle that revolves around the nucleus. So, Rutherford discovered the nucleus.

Drawbacks of Rutherford’s model of an atom:

The major drawback is the instability of the orbital revolution of an electron. If the electron moves around the nucleus at high speed, it will give up its energy and fall into the nucleus.

Bohr’s Model of an Atom:

According to this model, the electrons revolve around the nucleus in discrete orbits called energy shells or energy levels. Each energy level is associated with a definite amount of energy. The change in energy takes place when the atom jumps from one energy level to another level. The energy level present in an atomic structure is shown below:

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