Atomic Model (Part 2: The Dalton's Atomic Model)

Before you study this chapter, make sure you have read about how Democritus argued for the first time about the model of the atom. if not, can click here.

 After centuries of theories concerning the atomic model proposed by Democritus abandoned, then in the early 19-th century (1808), a British chemist and physicist, John Dalton studied thotoughly how different element, such as hydrogen and oxigen, could combin to form another substance, e.g. water. In his book A New System of Chemical Philosophy, Dalton made two assertions about atoms, ei:

•  Atoms of each element are all indentical to another, butdifferent from theatoms of all other element.
•  Atom of different element can combine to form more complex substance.

 Dalton's idea which points out that different element have different atoms is not similar to the Democritus' idea dealing with atoms. The properties of Dalton's atoms determine the chemical and physical properties of a substance. Farexample, carbon atoms can form both diamonds and graphite. In Dalton's theory, diamond atoms are very similar to graphite atoms because both substance are compose of the same chemical element. Meanwhile, according to the Democritus' idea, diamond atoms are very different from graphite atoms.

 Dalton observed that two element can combine in more than one way. For example, modern scientistc know that carbon monoxide (CO) and carbon dioxide (CO2) are compounds of both carbon and oxygen. Based on Dalton's experiment, the quantities of an element needed tto compose different compounds are always the round number multiplication of one another. For example, oxygen needed to form a liter of CO2 is twice as much as what is needed to form one liter of CO. Based on the result of his experiment, Dalton concluded that compound were created when atoms of pure element joined together to form a unit called molecule in fixed proportions. This Dalton's conclusion is also caled the double multiple law.

Next- Atomic Model (Part 3: The Thomson's Atomic Model)