Atomic Theory Timeline - In The Beginning

I think that the best format to present what I have discovered about the history of the Atomic Theory and how it directly relates the nature of science is by presenting it in a time line. I also think that this may be a useful assessment that could be used in a science classroom. It would be also neat to have students research one particular scientist and present their findings to the class. You could create a living timeline with your students.

DEMOCRITUS: 460 BCE - 370 BCE

Our current understanding of the atom has been in the making for thousands of years and began with the Greek philosophers/scientists. Prior to Democritus, Empedocles had described a theory that matter was composed of four core elements, water, fire, air, and earth. Empedocles theory was problematic as it did not describe why when you break a rock in half the pieces never resembled any of the core elements. Democritus developed a new theory to overcome the problems of his predecessor. He suggested that there were infinitesimally small pieces of matter which he called atomos, meaning 'indivisible.' Democritus suggested that atomos were eternal and could not be destroyed, and also that these atomos were unique to the material that they made up. This theory attempted to explain the whole physical world.

Improvements on previous model:

• Talks about the atom as the smallest particle of matter
• Defines the atom as an indivisible particle
• Attempts to explain the existence of elements

Key problems with the model:

• The view is not scientific but rather a conceptual definition of the atom
• Does not describe subatomic particles 

 JOHN DALTON: 1766 - 1844

Dalton was a British teacher and scientist who is credited with developing the first modern atomic theory in 1803. He used the foundations laid by other chemists Priestley and Lavoisier along with his own discoveries from studying weather to determine that matter must be composed of tiny particles. Dalton's theory is often referred to as the solid sphere model as Dalton pictured atoms as tiny billiard-ball like particles in various states of motion. There are four key concepts in Dalton's theory:

1. All matter is composed of indivisible particles called atoms
2. All atoms of a give element are identical; atoms of different elements have different properties
3. Chemical reactions involve the combination of atoms, not the destruction of atoms
4. When elements react to form compounds they react in defined, whole-number rations or in other words reactions are not random events. 

Improvements on previous model:

• Explains many chemical properties such as how atoms combine to form molecules
• Explains chemical change

Key problems with the model:

• Does not include the existence of the nucleus
• Does not explain the existence of ions or isotopes
• Does not describe subatomic particles

This concludes the first part of my Atomic Theory time line. It is obvious that scientists built upon the work of others to produce a more accurate explanation of the world. This is a great example of how the nature of science works and how incorrect theories can contribute to important scientific discoveries. 

Resources:

The vast majority of my information was found in the virtual textbook VisionLearning. This online source contains numerous modules with online quizzes and interactive links to aid in learning. The online source is presented like a interactive textbook and includes modules for numerous science topics form biology to chemistry and it is free.

In the Beginning