John Dalton developed the first useful atomic theory of matter around 1803. In the course of his studies on meteorology, Dalton concluded that evaporated water exists in air as an independent gas. Solid bodies can’t occupy the same space at the same time, but water and air could. If the water and air were made of discrete particles, evaporation might be viewed as a mixing of water particles with air particles. He performed a series of experiments on mixtures of gases to determine what effect properties of the individual gases had on the properties of the mixture as a whole. While trying to explain the results of those experiments, Dalton developed the hypothesis that the sizes of the particles making up different gases must be different.
Dalton’s exceptional gift for recognizing and interpreting patterns in experimental data lead him from a problem in meteorology to the idea of atoms as fundamental constituents of matter. He realized the vital theoretical connection between atomic weights and weight relations in chemical reactions. He was the first to associate the ancient idea of atoms with stoichiometry.
The existence of atoms was first suggested more that 2000 years before Dalton’s birth. (Newton’s speculations about atoms in the Principia were carefully copied by hand into Dalton’s notebooks.)
Atoms of an element cannot be created, destroyed, broken into smaller parts or transformed into atoms of another element. Dalton based this hypothesis on the law of conservation of mass and on centuries of experimental evidence.
Some of the details of Dalton’s original atomic theory are now known to be incorrect. But the core concepts of the theory (that chemical reactions can be explained by the union and separation of atoms, and that these atoms have characteristic properties) are foundations of modern physical science.
Most of Daltons ideas have changed in the scientific world by: 1. Many of his conclusions were concluded to be incorrect or false. 2. They were used them to explain some of the happenings of the universe and the world surrounding us (humans, animals etc.). 3. Some of the concepts of Daltons scientific findings are proven to be right. But they have changed in the past few years to be altered and edited.