5. Some Facts…..
It’s amazing to think about how life evolved on this planet. Ever since
our existence on this planet, the human brain has been curious to
understand nature. This curiosity has been the mother of all inventions.
There have been a number of theories to predict the same. One such
theory is the Dalton’s Atomic Theory. We will learn about this theory and
its postulates in this chapter. We will also look at is limitations. Let’s
begin.
Matter has been one of the most important subjects of research for the
science enthusiasts. Scientists and philosophers have always tried to
simplify things. They wanted to know about the fundamental particles
that make matter, their properties, structure etc. This led to the
formulation of a number of atomic theories.
6. ……
Democritus was the first man who proposed that matter is
made up of particles. He named these particles, ‘atomos’
meaning indivisible. This was the Democritus’ Atomic
Theory. Due to the lack of technological setup back then,
scientists had very limited information on this theory.
7. Almost after two thousand years, the works on the simplifying
matter was materialized by scientist, John Dalton. In 1808, John
Dalton postulated the famous Dalton’s Atomic Theory. He published
this theory in a paper titled “A New Chemical Philosophy”; indeed
the philosophy was new for that era. Let us now look at the
postulates of this theory. The below figure shows that matter made
up of smallest particle called atom.
8. In 1808, Dalton published ‘A New System of
Chemical Philosophy’, in which he proposed the
following :
9.
10. Dalton’s theory could explain the laws of
chemical combination. However, it could not
explain the laws of gaseous volumes. It could
not provide the reason for combining of atoms,
which was answered later by other scientists.
15. Since there were so many defects in Dalton’s atomic
theory, scientists started to carry out more
experiments to explain the exact structure and the
properties of an atom. This led to the development
of the modern atomic theory. The modern atomic
theory indicated the defects of Dalton’s atomic
theory. These defects can be stated as below.
16.
17. Nuclear Fission and Chain reaction of Uranium
Dalton’s said:
Atoms cannot be subdivided, created or destroyed
Modern theory states that: Atoms cannot be subdivided, created or
destroyed in ordinary chemical reactions. However, these changes
can occur in nuclear reactions.
18. Radioactive Decay
Radioactive decay (also known as nuclear decay, radioactivity, radioactive
disintegration or nuclear disintegration) is the process by which an unstable
atomic nucleus loses energy by radiation. A material containing unstable nuclei is
considered radioactive. Three of the most common types of decay are alpha
decay, beta decay, and gamma decay, all of which involve emitting one or more
particles or photons.
22. Summary – Dalton’s Atomic Theory vs Modern Atomic Theory
Even though there were no well-equipped laboratories,
Dalton was able to build up a theory on atoms, which are
invisible to the eye. This led to the development of modern
atomic theory, which can explain almost everything about
the structure and properties of atoms.
There is a large difference between Dalton’s atomic theory
and modern atomic theory since the structure and
properties of atom according to Dalton’s theory is
different from the structure and properties proposed by
the modern atomic theory.
