, The existence of different kinds of matter is due to
different atoms constituting them. Now the questions
arise:
(i) What makes the atom of one element different from
the atom of another element? and
(ii) Are atoms really indivisible, as proposed by Dalton, or
are there smaller constituents inside the atom?
We will learn about sub-atomic particles and the various
models that have been proposed to explain how these
particles are arranged within the atom.
For explaining this, many scientists proposed various
atomic models. J.J. Thomson was the first one to
propose a model for the structure of an atom.
,THOMSON’S MODEL OF AN ATOM
Thomson proposed the model of an atom to be similar to
that of a Christmas pudding. The electrons, in a sphere of
positive charge, were like currants (dry fruits) in a spherical
Christmas pudding. We can also think of a watermelon, the
positive charge in the atom is spread all over like the red
edible part of the watermelon, while the electrons are
studded in the positively charged sphere, like the seeds in
the watermelon.
Thomson proposed that:
(i) An atom consists of a positively charged sphere and the
electrons are embedded in it.
(ii) The negative and positive charges are equal in magnitude.
So, the atom as a whole is electrically neutral. Although
, Thomson’s model explained that atoms are electrically
neutral, the results of experiments carried out by other
scientists could not be explained by this model.
different atoms constituting them. Now the questions
arise:
(i) What makes the atom of one element different from
the atom of another element? and
(ii) Are atoms really indivisible, as proposed by Dalton, or
are there smaller constituents inside the atom?
We will learn about sub-atomic particles and the various
models that have been proposed to explain how these
particles are arranged within the atom.
For explaining this, many scientists proposed various
atomic models. J.J. Thomson was the first one to
propose a model for the structure of an atom.
,THOMSON’S MODEL OF AN ATOM
Thomson proposed the model of an atom to be similar to
that of a Christmas pudding. The electrons, in a sphere of
positive charge, were like currants (dry fruits) in a spherical
Christmas pudding. We can also think of a watermelon, the
positive charge in the atom is spread all over like the red
edible part of the watermelon, while the electrons are
studded in the positively charged sphere, like the seeds in
the watermelon.
Thomson proposed that:
(i) An atom consists of a positively charged sphere and the
electrons are embedded in it.
(ii) The negative and positive charges are equal in magnitude.
So, the atom as a whole is electrically neutral. Although
, Thomson’s model explained that atoms are electrically
neutral, the results of experiments carried out by other
scientists could not be explained by this model.
