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Atom and Atomic Theory
Matter can be either an element, a compound, or a mixture. The smallest component
of an element is called an atom. Each element is unique because of the different physical and
chemical properties of the atoms that comprise them. (Silberberg 41)
The curiosity for the composition of things started back ancient Greece. Philosophers
believed that at least one or all of the four elements – water, air, fire, and earth – were what
composed things around them. (Democritus first coined the term “atomos”, which means
“uncuttable”. He believed that anything could be broken down into infinitesimal particles.
This idea was dismissed for about 2000 years due to Aristotle’s wide influence. Fortunately,
English scientist Robert Boyle began the rediscovery of atoms in the 17th century. His idea
that “simple Bodies, not made of any other Bodies, of which all mixed Bodies are
compounded, and into which they are ultimately resolved,” sparked further studies. By the
19th century, John Dalton expressed his theory on atoms through four postulates. These
postulates eventually came to explain the mass laws – conservation of mass, definite
composition, and multiple proportions. (Silberberg 41-47)
However, with the discovery of atoms, many questions were still unanswered such as
mass of the atoms and existence of charged particles. J.J. Thomson discovered the negative
particles called electrons through cathode ray experiments. Soon thereafter, Ernest Rutherford
discovered the existence of a positively charged small, central core of mass, which is the
nucleus. Finally, the mass of atoms were resolved upon James Chadwick’s discovery of
neutron. (Silberberg 51)
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Works Cited
Silberberg, Martin. Chemistry: The molecular nature of matter and change. McGraw-Hill,
2007