Our understanding of the atom has changed remarkably over time. At one point, it was considered a solid object. Now, the atom is considered to have a cloud for its electrons. We believe that our notion of the atom has had many changes, and will continue to change until we get it right.
             The first scientist was Sir Isaac Newton. True, the atom was not his greatest achievement, but he had a mutual association with it. The latter part of Newton's book Optiks is a series of speculations on the atomic nature of matter, indicating how some of matter's properties are to be understood in terms of atoms. (http://physics.hallym.ac.kr/education/qm/mitqm/804f/.html) Newton needed the atom to help him write this book.
             Robert Boyle was similar to Newton in his association with the atom. Boyle's work in chemistry was aimed at establishing the atom as a rational theoretical science on the basis of a mechanistic theory of matter. Boyle was a skillful experimenter who insisted that experimentation was an essential part of scientific proof . (http://webpub.allegheny.edu/employee/g/grodgers/ScientificTravelingWebsite/Boyle.html)
             The atom also helped the famous chemist Mendeleev. Mendeleev was the chemist that made the periodic table. Mendeleev used the atom to help sort elements. He listed the elements by their atomic weight, (explained again in Dalton's paragraph). Also the smallest form of an element is the atom. We now know that the number of electrons, protons, and neutrons differs within each atom. (http://www.chemsoc.org/viselements/pages/history.html)
             John Dalton furthered our information on the atom. Dalton's main step forward was his introduction of atomic weights. He discovered the law of multiple proportions, which states that when several distinct reactions take place among the same elements, the quantities entering the reactions are always in the proportions of simple integers, 1 to 1, 2 to 1, 2 to 3, and so...