History of Atomic Theories - History of Atomic Theories 1...

History of Atomic Theories 1
History of Atomic Theories
John-Douglas McGregor
SCH4U
Somayeh Nikoudad
August 14
th
, 2014

History of Atomic Theories 2
History of Atomic Theories
This essay is an analysis of the significant Atomic Theories that lead to the Modern
Atomic Theory, the basis of chemistry ( Barron's E-Z chemistry , 2009). The following pages will
examine five different philosophers, theories: Democritus, John Dalton, J.J. Thompson, Ernest
Rutherford, Neils Bohr, Erwin Schrödinger and James Chadwick.
Democritus Atomic Theory:
The main idea of philosopher Democritus, who lived more than 2000 years ago, was that
an atom is an invisible and indestructible particle. Democritus was a man of Greek origin, so he
related his work back to his origins. For example the word atomos in ancient Greek means “that
which cannot be further broken down into smaller pieces.” (Lista, 2006) Democritus made 6
basic assumptions, known as the particle theory of matter.
Particle theory of matter (Lista, 2010):
1. Matter is made up of tiny particles (Atoms & Molecules)
2. Particles of Matter are in constant motion.
3. Particles of Matter are held together by very strong electric forces
4. There are empty spaces between the particles of matter that are very large compared to
the particles themselves.
5. Each substance has unique particles that are different from the particles of other
substances
6. Temperature affects the speed of the particles. The higher the temperature, the faster the
speed of the particles.
Democritus theory like most philosophers of his time was not based on scientific
examination/experiments. It was based on reasoning and assumptions.
Some shortcomings/problems with Democritus theory are that it does not give a specific
view of the atom only a theoretical definition and that it does not discuss subatomic particles
(electrons, neutrons, and protons). Democritus short comings left the way open for further
development on his theory.
John Dalton Atomic Theory:

History of Atomic Theories 3
Theories based on non-experimental trials continued until the eighteenth century. During
the eighteenth century scientific experimentation was on the rise and in 1805, John Dalton made
some of his own assumptions about atoms. The difference between Dalton and Democritus
assumptions is that, Dalton had experimental data to support his assumptions, and for this reason
is often identified as the father of modern atomic theory (Francis, 2002).
Dalton’s theory makes 5 main assumptions, known as the theory of simple multiple proportions
(Francis, 2002).
Dalton’s Atomic Theory (Theory of Simple Multiple Proportions):
1. All matter is made from tiny hidden particles, called Atoms.
2. All Atoms of a specific element are the same in weight and has a unique weight when
compared to other atoms.