10.3.4: Dalton's Atomic Theory

Learning Objectives

• Recognize the 5 tenants of Dalton's Atomic Theory.

Though we have illustrated our current knowledge of the behavior of atoms in our discussion of the laws of definite proportions and multiple proportions, this information was not available to Dalton when he formulated atomic theory. In fact, it was the information in the laws themselves which naturally led to the conclusion that atoms must exist. Using only the three laws we have introduced in this section, Dalton devised the atomic theory as an explanation for the observations which led to these laws. It was a scientific way of suggesting that atoms existed, as opposed to the non-scientific debates that the Greek philosophers engaged in. The general tenets of this theory are as follows:

• All matter is composed of extremely small particles called atoms.
• Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties.
• Atoms cannot be subdivided, created, or destroyed.
• Atoms of different elements can combine in simple whole number ratios to form chemical compounds.
• In chemical reactions, atoms are combined, separated, or rearranged.

Dalton's atomic theory has been largely accepted by the scientific community, with the exception of three changes. We now know that (1) an atom can be further subdivided, (2) all atoms of an element are not identical in mass, and (3) using nuclear fission and fusion techniques, we can create or destroy atoms by changing them into other atoms. We will explore each of these ideas later in this text. However, for any chemical reaction the ideas held within the atomic theory would correctly predict the results of that reaction.

---