-
500 BCE
The Alchemist
The Alchemist used symbols to identify elements, and made many important discoveries to the development to the modern science of chemistry. -
450 BCE
Aristotle
Aristotle did not believe in the atomic theory. 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. -
430 BCE
Democritus
He theorized that all material bodies are made up of invisibly small "atoms". convinced that atoms of matter must come from solids. -
400 BCE
Plato
Introduced the atomic theory which ideal geometric forms serve as atoms, according to which atoms broke down mathematically into triangles, such that form elements had a shape. -
Robert Boyle
Studied the possibility of atoms existing he attempted alchemy or turning regular metals into gold. he made gas chambers to study from. -
Lavoisier
"Father of Chemistry" created the law conservation of mass. -
Dmitri Mendeleev
Brought order to Dalton's atomic theory. Placed the elements in order of atomic weights and noticed that the properties of valence, or the ability that each type of atom has for combining with other atoms, had periodic nature. -
John Dalton
Dalton thought that atoms were the smallest particles of matter, he envisioned them as hard spheres, like billiard (pool) balls, so he used wooden balls to model them. -
J.J Thompson
Found that the electron is negatively charged on the atom. -
The Curies
Discover an isolate the radium, anew element which spontaneously disintegrated into other elements. This proved that atoms of one element at least were not visible. -
Albert Einstein
Biggest contribution to the atomic theory was that he was able to fully prove through usage of evidence that atoms did indeed exist. also able to demonstrate that elements could leave metal through usage of light. -
Ermest Rutherford
Envisioned the atom as a miniature solar system, with electrons orbiting around the nucleus and as mostly empty space with the nucleus occupying only a very small part of the atom. -
Neils Bohr
Proposed a model of an atom in which the electron was able to occupy only certain orbits around the nucleus. "solar system" was the name of the model. -
Henry G. J. Mosely
Major properties of an element are determined by the atomic number, not by the atomic weight and firmly established the relationship between atomic number and the charge of the atomic nucleus. -
Robert Millikan
His oil drop experiment confirmed the existence of the electron and accurately determined that its charge is negative. -
Werener heinsberg
used the electron cloud model to visualize the most probable position of the electrons in an atom.