NCERT Question 5 - Chapter 4 Class 9 - Structure of Atom

JJ Thomson’s

Plum Pudding Model

Rutherford’s Model

Bohr’s Model

Explanation of the model

As per Thomson, the Model of Atom is similar to a Christmas pudding.

1. Spherical pudding with dry fruits embedded in it.

2. Similarly atom is made up of positive charge with electrons embedded in it.

Rutherford's model of an atom stated that:

1. Electrons revolve in circular paths around positively charged centre called nucleus; constitutes nearly all the mass of an atom.

2. The size of the nucleus is very small in comparison with the atom.

Bohr’s model stated that:

1. Electrons move around Nucleus of an atom in discrete orbits.

called energy levels or shells.

2. Electrons keep on revolving in the same shell without radiating energy.

Limitations

Model could explain the neutral nature of an atom, but not the results of the experiments like Rutherford’s alpha particle scattering experiment

When a charged particle like an electron moves in a circular path, it would accelerate and lose energy and ultimately fall into the nucleus, thus making it unstable. But, it doesn't really happen and Rutherford couldn’t explain. 

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Representation of the model