Principles Of General Chemistry II CHEM121
Thompson’s model of atom and its limitations
In his famous paper in 1897, J.J. Thomson wrote: “The electron is a particle which
is emitted by the atoms of matter. Its mass is negligible compared with that of the
atom, and therefore its influence upon the motion of the atom may be disregarded.”
Thomson’s hypothesis was based on an unproved hypothesis called wave-particle
duality. This hypothesis states that particles exhibit both properties at the same time
and cannot be separated from each other. Therefore, Thomson assumed that light
behaves like a wave but also as a particle. He was wrong. Light does not behave as
both a wave and a particle. It is best described as a wave. Particles are much smaller
than waves, they are indivisible J.J Thomson proposed it in 1904, shortly after the
discovery of electrons. However, the atomic nucleus had not yet been discovered at
the time. As a result, he proposed a model based on known properties available at
the time. Atoms are neutrally charged, according to known properties. An atom
contains negatively charged particles known as electrons.
Thomson's atomic model postulates that an atom resembles a positive-charged
sphere with electrons (negatively charged particles) present inside. Because the
magnitude of the positive and negative charges is equal, an atom has no charge
overall and is electrically neutral. Thomson's atomic model is shaped like a spherical
plum pudding and a watermelon. It is similar to plum pudding because the electrons
in the model resemble the dry fruits embedded in a positive charge sphere, just like
a spherical plum pudding.
