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550 BCE
Aristotle
Aristotle opposed the Atomic theory developed by Democritus. He believed that matter was not made of tiny particles (atoms) that they were all fundamentally air, fire, water, and earth. -
500 BCE
Alchemy
Alchemist. Alchemists - 500BC-1720--- Developed the theory—that all metals are composed of mercury and sulfur and that it is possible to change base metals into gold. The ancient Chinese were performing Alchemy as early as 500 B.C. -
401 BCE
Leucippus
Leucippus' believed that the world was composed of an infinite number of solid, indestructible, indivisible atoms that interact with one another. What separates the atoms is the void, which is basically empty space. -
400 BCE
Democritus
Democritus contributed to the theory of atomism by suggesting that all matter consisted of tiny, inseperable particles. -
1494
George Bauer
George Bauer was a German scientist, who created the first scientific classification of minerals based on their physical properties and named many new minerals and their occurence. -
1527
Paracelsus
Paracelsus was a natural philosopher in the16th-century. He contributed a lot to the history of chemistry, putting together in the Aristotelian theory of matter, alchemical correspondences, mystical forms of knowledge, and chemical therapy in medicine. -
Robert Boyle
Robert Boyle was a natural philosopher, chemist, physicist, and inventor. Boyle is largely regarded today as the first modern chemist, and therefore one of the founders of modern chemistry, and one of the engineers of the modern experimental scientific method. -
Amadeo Avogadro
Amedeo Avogadro was an Italian scientist who is best known for his hypothesis, now known as Avogadro's law. His hypothesis stated that equal volumes of different gases contain an equal number of molecules, provided they are at the same temperature and pressure. His hypothesis was rejected by other scientists, but gained acceptance after his death. -
Antoine Lavoisier
Antoine Lavoisier was a French chemist who had a huge impact on the 18th-century chemical revolution and who had a large influence on both the history of chemistry and the history of biology. Lavoisier is well known for his discovery of the role oxygen plays in combustion. He recognized and named oxygen and hydrogen and opposed the phlogiston theory. Lavoisier helped construct the metric system, wrote the first extensive list of elements, and helped to reform chemical nomenclature. -
John Dalton
John Dalton was an English chemist, physicist, and meteorologist. He is best known for introducing the atomic theory into chemistry. The main points of Dalton's atomic theory are: Elements are made of extremely small particles called atoms. Atoms of a given element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties. Atoms cannot be subdivided, created or destroyed. -
Joseph Proust
Joseph Proust first published his Law of Definite Proportions (or Law of Constant Composition) in 1794. This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created. -
Jons Jakob Berzelius
Jons Jakob Berzelius was a chemist from Sweden who was one of the first European scientists to believe John Dalton's atomic theory and think it necessary to revamp the chemical symbol system. He established the law of constant proportions, which says that the elements in inorganic substances are bound together in definite proportions by weight. -
Joseph Gay-Lussac
Joseph Louis Gay-Lussac was a French chemist and physicist. He is known mostly for his discovery that water is made of two parts hydrogen and one part oxygen and the work he did on alcohol-water mixtures, which led to the degrees Gay-Lussac used to measure alcoholic beverages in many countries. -
Max Planck
Max Planck was a German physicist. In 1900, Planck made the assumption that energy was made of individual units, or quanta. In 1905, Albert Einstein theorized that not just the energy, but the radiation itself was quantized in the same manner.The Development of Quantum Theory. -
Robert Millikan
Robert Millikan was an American physicist, born in 1868. His oil drop experiment played a major role in quantifying the charge of an electron. This contributed greatly to our understanding of the structure of the atom and atomic theory. -
Ernest Rutherford
Ernest Rutherford created the gold foil model, and in 1911, he was the first to discover that atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons, which became known as the Rutherford model (or planetary model) of the atom. -
Niels Bohr
Niels Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another. -
Erwin Schrodinger
Erwin Schrödinger was an Austrian physicist who developed an “Electron Cloud Model” in 1926. It consisted of a dense nucleus surrounded by a cloud of electrons at various levels in orbitals. -
Louis de Broglie
Louis de Broglie was an eminent French physicist. He gained admiration for his groundbreaking work on quantum theory. In his 1924 thesis, he discovered the wave nature of electrons and suggested that all matter have wave properties. -
Arthur Compton
Compton was an American physicist and winner of the Nobel Prize in Physics. He is best known for demonstrating the "Compton effect," which occurs when high energy photons (such as X-rays) collide with a target and transfer part of that energy to a single electron -- supporting Einstein's particle theory of light. Compton shared the 1927 Nobel Prize in Physics for this discovery. -
Henri Becquerel
In 1896 Henri Becquerel was using naturally fluorescent minerals to study the properties of x-rays, which had been discovered in 1895 by Wilhelm Roentgen. This lead to his discovery of radioactivity. Becquerel realized that some invisible radiation had been emitted from the uranium. He won the Nobel Prize in 1903, along with Marie and Pierre Curie, for his discovery, and the SI unit of radioactivity, the becquerel (Bq), was named after him. -
Werner Heisenberg
Heisenberg was a German theoretical physicist and one of the key pioneers of quantum mechanics. He published his work in 1925 in a breakthrough paper. In the subsequent series of papers with Max Born and Pascual Jordan, during the same year, this matrix formulation of quantum mechanics was substantially elaborated. He is known for the Heisenberg uncertainty principle, which he published in 1927. -
Plum Pudding Model
The Plum Pudding Model is a model of atomic structure proposed by J.J. Thomson in the late 19th century. Thomson had discovered that atoms are composite objects, made of pieces with positive and negative charge, and that the negatively charged electrons within the atom were very small compared to the entire atom. -
Planetary Model
Created by Ernest Rutherford in 1911 and is sometimes called the Rutherford model. The model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun. -
Bohr Model
The Bohr model was devised by Neils Bohr. Bohr proposed, as did Rutherford, that the atom had a small, positive nucleus where most of its mass resided. He stated that the electrons orbited around this nucleus like planets around the sun. The main improvement of Bohr's model was that the electrons were confined to set orbits around the nucleus, each having a specific energy level, which explained experimental observations such as electromagnetic radiation. -
Electron Cloud Model
The electron cloud model is currently the most sophisticated and widely accepted model of the atom. It retains the concept of the nucleus from Bohr and Rutherford's models, but introduces a different definition of the motion of electrons around the nucleus. The movement of electrons around the nucleus in this model is defined by regions where there is a greater probability of finding the electron at any given moment. -
J. J. Thomson
Sir Joseph John Thomson OM PRS was an English physicist and Nobel Laureate in Physics, credited with the discovery and identification of the electron; and with the discovery of the first subatomic particle. His research in cathode rays led to the discovery of the electron, and he pursued further innovations in atomic structure exploration.
