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500 BCE
The Alchemist
The Alchemist proposed the idea that all metals are composed of mercury and sulfur and that it is possible to change base metals into gold. Dalton's most important contribution to science was his theory that matter is composed of atoms of differing weights and combine in simple ratios by weight. -
500 BCE
Democritus
The theory of Democritus held that everything is composed of the atoms which are physically, but not geometrically, indivisible; that between atoms, there lies empty space; that atoms are indestructible, and have always been and always will be in motion; that there is an infinite number of atoms and of kinds of atoms. -
427 BCE
Plato
The Plato postulated that a fifth atomic type must exist which Aristotle later called. The heavens, and objects in the heavens are stars, planets, and the sun and they are all composed of atoms. This is perhaps the first example of the use of theoretical thought experiments to predict or postulate new concepts. -
340 BCE
Artisole
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. And he is correct about the 4 elements made up of the atoms. -
Robert Boyle
Robert Boyle's major contribution to the atomic theory was that he helped develop a definition of an element. -
Lavoisier
The first breakthrough in the study of chemical reactions resulted from the work of Lavoisier between 1772 and 1794. Lavoisier found that mass is conserved in a chemical reaction. -
John Dalton-- Billiard Ball
John Dalton believed that all substances are made of atoms. Atoms are the smallest particles of matter. They cannot be divided into smaller particles, created, or destroyed. -
Dmitri Mendeleev
On 17 February 1869, Russian chemist Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order helped out be doing the weight work so therefore someone else didnt have to spend their time weighing the atomic weights. -
The curies
Curie conducted her own experiments on uranium rays and discovered that they remained constant. The rays she theorized, came from the element's atomic structure. This revolutionary idea created the field of atomic physics. -
plum pudding model-
The plum pudding model was first proposed by J.J Thomson. Before the discovery of the atomic nucleus, the model tried to explain two properties of atoms then known: that electrons are negatively-charged particles and that atoms have no net electric charge. -
Ernest Rutherford
Ernest Rutherford postulated the nuclear structure of the atom. He received the Nobel Prize in Chemistry in 1908. -
Robert Millikan
Robert's earliest major success was the accurate determination of the charge carried by an electron, using the elegant falling-drop method he also proved that this quantity was a constant for all electrons thus demonstrating the atomic structure of electricity. -
solar system model-Neils Bohr
The solar system model of the atom describes atoms as consisting of a nucleus with a number of electrons in orbits around that nucleus, similar to a solar system. -
Henry G. J. Mosely
In 1913, while working at the University of Manchester, he observed and measured the X-ray spectra of various chemical elements using diffraction in crystals. Through this, he discovered a systematic relation between wave- length and atomic number. This discovery is now known as Moseley's Law. -
Werner Heisenberg-- Electron Cloud model
Erwin Schrödinger invented the Electron cloud model. It consisted of a dense nucleus surrounded by a cloud of electrons at various levels in orbitals. Schrödinger and Werner Heisenburg mathematically determined regions in which electrons would be most likely found. -
Albert Einstein
In 1938, three chemists working in a laboratory in Berlin made a discovery that would alter the course of history: they split the uranium atom. This was strong enough to explode a bomb.
