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450 BCE
John Dalton
Dalton hypothesized that the law of conservation of mass and the law of definite proportions could be explained using the idea of atoms. -
428 BCE
Plato
Came up with elements -
400 BCE
Democritus
the Greek philosopher Democritus introduced the idea of the atom as the basic building block matter. -
300 BCE
Aristotle
Aristotle believed that elements were the building blocks of chemical substances, only potentially present in these substance -
Robert Boyle
He thought of the possibility of atoms existing, but his work was greatly diagreed by the church. -
Lavoisier
Antoine Lavoisier was a key figure in the field of chemistry in the late 18th century. He consolidated the research of many of his contemporaries into a coherent theory of elements, which he defined as indivisible particles which we have found no means of separating. -
The alchemists
His first discussion of these issues dates to 1803, and he presented his atomic theory in the multivolume New System of Chemical Philosophy. -
solid Sphere of "Billiard Ball" Model
Because Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. -
Dmitri Mendeleev
Dmitri Mendeleev devised the periodic classification of the chemical elements, in which the elements were arranged in order of increasing atomic weight. -
Photoelectric Effect
The photoelectric effect proves that light has particle-like activity. The photoelectric effect happens when photons are shone on metal and electrons are ejected from the surface of that metal -
Planck's Quantum Theory of Light
The timeline of quantum mechanics is a list of key events in the history of quantum mechanics, quantum field theories and quantum chemistry. -
The Curies
The Curies shared the 1903 Nobel Prize in physics with Antoine Henri Becquerel. -
"Plum Pudding" Model
The plum pudding model is one of several historical scientific models of the atom. First proposed by J. J. Thomson in 1904 -
Albert Einstein
Einstein also in 1905 mathematically proved the existence of atoms, and thus helped revolutionize all the sciences through the use of statistics and probability. -
Ernest Rutherford
Concluded a small, dense, positively charge nucleus as the result of the alpha particles scattering gold foil experiment -
Robert Millikan
During the 1890s the theory that electricity was conveyed by a miniscule unit, the electron, gained acceptance. In 1910 Robert Millikan succeeded in precisely determining the magnitude of the electron's charge. -
Neils Bohr
In July of 1913, Danish physicist Niels Bohr published the first of a series of three papers introducing this model of the atom, which became known simply as the Bohr atom -
Solar System Model
The "solar system" model describes an atom as a central massive positive entity (the nucleus/sun) and, orbiting around it, the negative entities (the electrons/planets). -
Henry G. J. Mosely
Physicist Henry Moseley discovered the atomic number of each element using x-rays, which led to more accurate organization of the periodic table. -
James Chadwick
By 1920, physicists knew that most of the mass of the atom was located in a nucleus at its center, and that this central core contained protons. -
Schrodinger Equation
Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. -
Electron Cloud Model
we cannot know exactly where an electron is at any given time, but the electrons are more likely to be in specific areas. -
J.J. Thomson
In 1904, Thomson proposed a model of the atom as a sphere of positive matter with electrons positioned based on electrostatic forces. So, he not only discovered the electron but determined it was a fundamental part of an atom. -
Werner Heisenberg
Heisenberg was a main contributor to the German atomic program during World War II, in direct competition with the Manhattan Project.
