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500 BCE
The Alchemists
The alchemists began examining the atomic theory about two centuries after the death of Aristotle. They used Aristotle’s idea about matter and began to create experiments and activities with them. By treating different metals and ores, the goal was to change the structure of the item so that it could become more valuable. Although the alchemists failed to turn common items into gold, they did create a scientific process which would allow for the eventual discovery of the atom. -
460 BCE
Democritus
Contribution to atomic theory. "By convention bitter, by convention sweet, but in reality atoms and void". Democritus said that everything is made up into tiny bits, which are called atoms. These atoms are indestructible. He said that different shapes of atoms gave them different properties. For example, he said that things that tasted sweet were made of round atoms. -
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). -
340 BCE
Aristotle
Aristotle contribution to atomic theory
Aristotle believed that all matter was made up either of one of the elements of water air earth and fire or combinations of these four elements, with the exception of stars and planets which were made of aether. Aristotle's theory of matter has been proven -
Robert Boyle
Robert Boyle (1627-1691) is known as “The Father of Chemistry” for his discovery that atoms must exist based on the relationship between pressure and volume of gas. His theorem called Boyle’s Law reasons that because a fixed mass of gas can be compressed, gas must be made of particles, or atoms, because there is space between them. -
Lavoisier
Antoine Lavoisier and the Atomic Theory. Born in 1743, Antoine Lavoisier is credited as being the first person to make use of the balance. He was known for his skills in experimentation and loved to separate the oxygen molecule from HgO. This led him to come up with the Law of Conservation, which states that matter is unable to be made or destroyed. -
John Dalton
Dalton’s Atomic Theory. The main points of Dalton’s atomic theory are: Everything is composed of atoms, which are the indivisible building blocks of matter and cannot be destroyed. All atoms of an element are identical. -
Solid Sphere Model
The Solid Sphere Model was the first atomic model and was developed by John Dalton in the early 19th century. He hypothesized that an atom is a solid sphere that could not be divided into smaller particles. He came up with his theory as a result of his research into gases. He realized that certain gases only combined in specific proportions. -
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. -
Plum Pudding
The plum pudding model is one of several historical scientific models of the atom. First proposed by J. J. Thomson in 1904 soon after the discovery of the electron, but 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 -
JJ Thomson
J.J. Thomson is credited with the discovery of the electron, the negatively charged particle in the atom. He is known for the Thomson atomic theory. Many scientists studied the electric discharge of a cathode ray tube. It was Thomson's interpretation that was important. -
The Curies
Atomic Theory of Matter Ninety years later, Pierre and Marie Curie were to discover and isolate radium, a new element which spontaneously disintegrated into other elements. This proved that the atoms of one element at least were not indivisible. -
Albert Einstein
Einstein's biggest contribution to the Atomic Theory was that he was able to fully prove through usage of evidence that atoms did indeed exist, and he was also able to demonstrate that electrons could leave metal through usage of light. He also created the mass energy equivalence equation, and this paved the way for the creation -
Ernest Rutherford
Rutherford model, description of the structure of atoms proposed (1911) by the New Zealand-born physicist Ernest Rutherford. The model described the atom as a tiny, dense, positively charged core called a nucleus, around which the light, negative constituents, called electrons, circulate at some distance. -
Robert Millikan
Millikan thought his cosmic ray photons were the "birth cries" of new atoms continually being created by God to interact entropy and prevent heat death. Robert Millikan was Vice Chairman of the National Research Council during World War I. During that time, he helped to develop anti-submarine and meteorological devices. -
Neils Bohr
Niels Bohr proposed a model of the atom in which the electron was able to occupy only certain orbits around the nucleus. This atomic model was the first to use quantum theory, in that the electrons were limited to specific orbits around the nucleus. Bohr used his model to explain the spectral lines of hydrogen. -
Henry G J Mosely
Henry Moseley, in full Henry Gwyn Jeffreys Moseley, (born November 23, 1887, Weymouth, Dorset, England—died August 10, 1915, Gallipoli, Turkey), English physicist who experimentally demonstrated that the 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. -
Solar System Model
Solar System models, especially mechanical models, called orreries, that illustrate the relative positions and motions of the planets and moons in the Solar System have been built for centuries. While they often showed relative sizes, these models were usually not built to scale. The enormous ratio of interplanetary distances to planetary diameters makes constructing a scale model of the Solar System a challenging task. -
Werner Heisenberg
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. The combined uncertainty in both measurements must be equal to or greater than h/(4π), where h is Planck’s constant. -
Electron Cloud Model
The electron cloud model was developed in 1926 by Erwin Schrödinger and Werner Heisenberg. The model is a way to help visualize the most probable position of electrons in an atom. The electron cloud model is currently the accepted model of an atom.
