-
Isaac Newton
Newton published an article stating his belief in the atomic nature of elements. He proposed a mechanical universe with small solid masses in motion. -
Robert Boyle
Boyle published an article stating his belief in the atomic nature of elements. -
John Dalton
Dalton stated that all matter is composed of very small particles called atoms, and that these atoms cannot be broken into smaller particles. -
Antoine Lavoisier
Lavoisier found that when a chemical change occurred in a closed system, the mass after a chemical change equaled the mass before the change. He proposed that matter can be changed in many ways, but it can never be created or destroyed. -
Joseph Proust
Proust had observed that specific substances always contain elements in the same ratio by mass. His principle is now known as the law of definite proportions. -
J.L. Gay-Lussac
Gay-Lussac noted that, under constant conditions, the volumes of reacting gases and gaseous products are always in the ratio of small whole numbers. He discovered this while studying gas reactions at constant temperature and constant pressure. -
Amedeo Avogadro
Avogadro stated that equal volumes of gases, under the same conditions, always have the same number of molecules. He explained Gay-Lussac's observation using Dalton's theory. -
Robert Millikan
Millikan obtained the first accurate measurement of an electron's charge. He used an oil drop apparatus like the one pictured. -
Henri Becquerel
Becquerel found that matter containing uranium exposes sealed photographic film -
J.J. Thomson
Thomson discovered electrons by doing skillful research on cathode rays. He measured the bending of the path of cathode rays to determine the ratio of an electron's charge to its mass. -
Alber Einstein
Einstein explained the origin of the energy released during nuclear changes. He hypothesized that mass and energy are equal. Hence, the famous formula e=mc^2 -
Henry Moseley
Moseley discovered that the number of protons determines the identity of the element and the number of neutrons determines the particular isotope of the element. He found this out while studying X rays produced in X-ray tubes with anodes of different metals. -
Lord Rutherford
Rutherford predicted the existence of the third particle in an atom (the neutron). -
Walter Bothe
Bothe obtained the first evidence of the third particle of an atom (the neutron). -
James Chadwick
Chadwick repeated Bothe's work. (He obtained evidence of the neutron.) -
Marie and Pierre Curie
Using Becquerel's previous discovery, the Curies found that rays are given off by uranium and radium.
