By the 18th century scientists had done thousands of experiments on the properties of matter and had formulated laws such as the Law of Conservation of Matter, and the Law of Multiple Proportions. Compounds can be separated into their constituent elements, but elements cannot be further subdivided. Thus, atoms are the building blocks of matter on the atomic scale, elements are the building blocks of matter on the macroscopic level. These laws allowed John Dalton, an English school teacher, to formulate a more modern version of the atomic model. Atoms of different elements are different.
Compounds consist of combinations of atoms of different elements in whole number ratios.
In fact, Dalton probably visualized sodium chloride pretty much as shown in Figure 7. Dalton's atomic theory helped chemists to understand the laws that had been formulated and many of the observations that had been made. Like most theories, however, within 50 years it was shown to be wrong in several respects. Around the turn of the century, chemists found evidence that atoms are not the solid, indivisible entities that Dalton imagined. After these subatomic particles were discovered, chemists and physicists naturally speculated about the structure of the atom.