9th Class Science Structure of the Atom Thomsons Model of Atom

        Thomson's Model of Atom

Thomson proposed the model of atom before the discovery of neutrons. According to his model, an atom consists of a positively charged sphere and electrons are embedded in it. The positive and negative charge are equal in magnitude that’s why atom is electrically neutral. His model was also known as watermelon model of an atom. Although Thomson's model was electrically neutral, but other scientist could not explain this model and hence was not accepted.

            Drawback of Thomsons Model

Some of the drawbacks of Thompson's model of atom were:

• Since the weight of an electron is about a thousandth part of a hydrogen atom, it would mean that a single atom, especially of the heavier elements/ would contain many thousand electrons. But J.J. Thomson himself found that the number of electrons in an atom cannot be greatly different from the atomic weight.
• According to this model, hydrogen can give rise to only one spectra! line, contrary to the observed fact of several lines.
• This model could not explain the large angle scattering of alpha particles by thin metal foils..