Lesson 3-1 The Development of the Atomic Theory

Lesson 3-1

Development of The Atomic Theory

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Development of the Atomic Theory

The concept of atoms, as you will learn, is quite old. The ancient Greeks had an atomic theory more than 2000 years ago. It is interesting to note that the idea originated from philosophy, and was based on reason rather than data. It is also interesting to note that, for many scientists, the final "proof" of the existence of atoms was provided by a, then-unknown 26 year old man named Albert Einstein. The story of the atom makes for interesting reading, and it involves a huge cast of characters whose lives spanned thousands of years. I have found some excellent essays on the internet. Follow the links below and enjoy.

I. The Greek Concept of Atomos - by John L. Park

II. Greek Theory and Roman Practice - by James A. Plambeck

III. Middle Ages Through Alchemy - by James A. Plambeck

IV. Two Centuries of Transition - by James A. Plambeck

The Modern Atomic Theory

John Dalton, an English chemist, might be called "the father of the modern atomic theory." During the early 1800's, Dalton's interests in Meteorology and gases lead him to read the works of Antoine Lavoisier and Joseph Proust. Lavoisier had stated the law of conservation of mass, that the mass of materials before a chemical reaction takes place is exactly equal to the mass of the materials after the reaction is completed. Proust had observed the law of definite proportions, stating that the proportion by mass of the elements in a given compound is always the same. Dalton felt that the findings of these men gave strong support to the idea of atoms. He formulated an atomic theory that would include the observations found by Lavoisier and Proust.

Dalton's Atomic Theory

1) All elements are composed of atoms, which are indivisible and indestructible particles.

2) All atoms of the same element are exactly alike; in particular, they all have the same mass.

3) All atoms of different elements are different; in particular, they have different masses.

4) Compounds are formed by the joining of atoms of two or more elements. In any compound , the atoms of the different elements in the compound are joined in a definite whole-number ratio, such as 1 to 1, 2 to 1, 3 to 2, etc.

Much has happened since the time of Dalton, which has made it necessary to update his atomic theory. We currently believe that all elements are composed of atoms, but we know that those atoms are not indestructible. Atoms are split in nuclear reactions, and they are made up of even smaller particles. We also know that atoms of the same element can have different masses, when they represent different isotopes. Despite these differences, much of Dalton's atomic theory remains useful to this day.

Development of the Atomic Theory Quizzes

Review 3-1c - The Atomic Theory By Jagdat Singh, Class of 2003

Development of the Atomic Theory Worksheets
	Worksheet 3-1a - which goes with lesson I above.
	Worksheet 3-1b - which goes with lesson II above.
	Worksheet 3-1c - which goes with lesson III above.
	Worksheet 3-1d - which goes with lesson IV above.
	Worksheet 3-1e - comparing Dalton's theory to the modern atomic theory.