Thomson’s Model of an Atom – Class 9 Tutorial

January 3, 2020 0 By Kody Olson


THOMSON’S MODEL OF AN ATOM Atoms are the basis of chemistry and of everything
in the Universe. Atoms are the general term used to describe
pieces of matter, i.e., matter is composed of atoms. That brings us to the question,
What is an atom? So, what is an Atom? The atom is a basic unit of matter that consists
of a dense central nucleus surrounded by a cloud of negatively charged electrons.
Studies of the atom date back as far as the 5th century BC.
Democritus, a Greek philosopher, described the atom as that which cannot be cut up further.
Acharya Kanada of India defined an atom as eternal and indestructible and which cannot
exist in free state. John Dalton proposed that atom was indivisible
and indestructible. However, this can only be true if it is not composed of further particles.
Are there particles that are smaller than an atom? Sure there are. The discovery of
fundamental particles called protons, neutrons and electrons inside the atom led to the failure
of Dalton’s atomic theory. This also proved void Democritus and Kanada’s theories that
the atom is indestructible. Who were the people behind the discoveries
of these particles? They were none other than: James Chadwick who discovered the neutron;
Eugene Goldstein who discovered the proton and J.J Thomson who discovered the electron. How do we explain the arrangement of protons
and electrons inside an atom? To explain the arrangement of protons and
electrons inside the atom, J.J. Thomson proposed a model for the structure of an atom, known
as Thomson’s Model of an Atom. The model of an atom proposed by Thomson is
similar to a Christmas pudding. In this model, electrons are arranged in a sphere of positive
charge, like a plum in a spherical Christmas pudding. So it is called the plum pudding
model of an atom. Do you know of any fruit that we can compare
Thomson’s atom model to? Well, it can be compared to a watermelon.
The negative charged electrons are like seeds embedded all over the positively charged sphere,
which is compared to the edible part in the watermelon. Thus, Thomson proposed that: An atom consists of a positively charged sphere
and electrons, which are embedded in it. The negative and positive charges are equal
in magnitude. So, the atom as a whole is electrically neutral. Things to Remember: Atoms are the basis of chemistry and of everything
in the Universe. Democritus, described the atom as that which
cannot be cut up further. James Chadwick discovered the neutron, Eugene
Goldstein discovered the proton and J.J Thomson discovered the electron.
The model of an atom proposed by Thomson is similar to a Christmas pudding
In this model, electrons are arranged in a sphere of positive charge, like plum in a
spherical Christmas pudding. The negative and positive charges are equal
in magnitude. So, the atom as a whole is electrically neutral.