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500 BCE
the alchemists
He invented the atomic theory that all metals are composed of mercury and sulfur. He also invented the theory that all base metals can be turned into gold. -
427 BCE
Plato
Plato introduced the atomic theory in which ideal geometric forms serve as atoms, according to which atoms broke down mathematically into triangles, such that the form elements had the following shape: fire (tetrahedron), air (octahedron), water (icosahedron), earth (cube). -
400 BCE
Democritus
A wise Greek philosopher that is most widely know for his atomic theorem of the universe. This states that everything in the universe is made up of matter and matter consists of atoms. -
385 BCE
Aristotle
Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. -
Robert Boyle
Robert Boyle's major contribution to the atomic theory was that he helped develop a definition of an element ( any substance that can be broken into 2 or more substances is not an element) and helped with " the death" of the four elements -
Lavoisier
Lavoisier was most well known for his contributions to the understanding of mass in chemical reactions such as measuring weight. He also made strides in understanding combustion. -
john dalton
Dalton did many experiments with gases as he strived to learn more about them. Dalton's experiments on gases led to his discovery that the total pressure of a mixture of gases amounted to the sum of the partial pressures that each individual gas exerted while occupying the same space. -
Dmitri mendeleev
Mendeleev found that, when all the known chemical elements were arranged in order of increasing atomic weight, the resulting table displayed a recurring pattern, or periodicity, of properties within groups of elements. ... He even predicted the likely properties of three of the potential elements. -
J.J. Thomson
J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." -
Henry G. J. Mosely
In 1913 he used self-built equipment to prove that every element's identity is uniquely determined by the number of protons it has. His discovery revealed the true basis of the periodic table and enabled Moseley to predict confidently the existence of four new chemical elements, all of which were found -
The Curies
Pierre and Marie Curie are best known for their pioneering work in the study of radioactivity, which led to their discovery in 1898 of the elements radium and polonium. She was honored with a Nobel prize, but later faced major health problems because of her exposure to radiation. -
Werner Heisenberg
How did Werner Heisenberg contribute to atomic theory? Werner Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly -
Albert Einstein
Albert Einstein had many scientific accomplishment, his contribution to the atomic model was the atomic view of matter. According to the atomic view of matter, a liquid is made up of a huge number of molecules in random, ceaseless motion, the properties of the liquid arising from the average behavior of its constituent molecules. -
Robert Millikan
Milikan began experiment to measure the charge of a single electron by measuring the course of charged water droplets in an electric field. This was not enough proof so instead he had to replace water and use oil in his experiment. -
Ernest Rutherford
Rutherford postulated the nuclear structure of an atom by "experiments done in Rutherford's laboratory showed that when alpha particles are fired into gas atoms, a few are violently deflected, which implies a dense, positively charged central region containing most of the atomic mass." He did his through the gold foil experiment. -
Neils Bohr
Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits.
