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500 BCE
Alchemists
The alchemists discovered the transmutation of substances from common metals into silver or gold and became the predecessors of modern science in several ways (mainly chemistry). They experimented with matters by treating metals and ores, and structurally changed the item to increase its value. Their experiments and failures led to the discovery of the atom. Their studies of natural processes advanced atomic theory, and laid down the foundation of the modern-day periodic table of elements. -
500 BCE
Leucippus of Miletus and Democritus of Abdera
The two Greek philosophers came up with the idea that all matter is made up of tiny, indivisible particles (atoms). The word "atom" originates from the Greek word "atomos", meaning "indivisible". Furthermore, they also believed that the atoms were completely solid, with no internal structure, and came in an infinite variety of shapes and sizes, accounting for different kinds of matter. Even intangible qualities like color and taste were thought to be composed of atoms. -
Period: 500 BCE to
Alchemists
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Period: 494 BCE to 434 BCE
Empedocles
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Period: 460 BCE to 370 BCE
Democritus
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440 BCE
Empedocles
Empedocles devised a theory of natural selection; proposed that everything is made from the four pure, indestructible elements: air, fire, wind, and earth; recognized that air has weight; came up with the claim that the speed of light is finite; and came up with a statement similar to the law of conservation of mass. His four-element theory stated that all matter was made from the four elements and are conscious, and this theory was popularized by Aristotle, becoming remarkably long-lived. -
Period: 384 BCE to 322 BCE
Aristotle
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360 BCE
Aristotle
Aristotle provided opposite viewpoints to the atomic theory, as he thought that all materials on Earth are made of the five elements: earth, fire, water, air, and aether. He influenced the public's belief and view on the existing small particles called atoms for about 2000 years. Although his theory of matter was proven wrong, it did contribute to the modern atomic theory by introducing and implying the existence of elements. Unfortunately, he also delayed the emergence of the atomic theory. -
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Isaac Newton
Newton was the culminating figure of the Scientific Revolution of the 17th century. In optics, he discovered the composition of white light, which integrated the phenomena of colors into the science of light, laying the foundation for modern physical optics. In mechanics, his three laws of motion became the basic principles of modern physics, and in math, he discovered the infinitesimal calculus. -
Isaac Newton
Newton laid the foundation of modern atomic theory alongside Robert Boyle, as he described the attractive and repulsive forces of objects having some impact on pressure. -
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Charles-Augustin de Coulomb
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Antoine Lavoisier
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John Dalton
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Antoine Lavoisier
Lavoisier discovered that mass is conserved in a chemical reaction (the total mass of the products of a chemical reaction is always the same as the total mass of the reactants consumed in the reaction), leading to the breakthrough and discovery of one of the fundamental laws of chemical behaviors: the law of conservation of matter. Furthermore, he also produced the first table of elements, though still incomplete at the time, which stimulated and influenced more chemical research. -
Charles-Augustin de Coulomb
Coulomb formulated the Coulomb law, which states that the force between two electrical charges is proportional to the product of the charges and inversely proportional to the square of the distance between them. The Coulombic force is one of the principal forces involved in atomic reactions. He established the inverse square law of attraction and repulsion of unlike/like magnetic poles, becoming the basis for the mathematical theory of magnetic forces. The unit coulomb was named in his honor. -
Period: to
Michael Faraday
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John Dalton
Dalton proposed the atomic theories that all matter is made of atoms (which are indestructible and indivisible), that all atoms of a given element are identical in mass and properties, that compounds are formed by a combination of two or more different kinds of atoms, and that a chemical reaction is a rearrangement of atoms. His theory became the theoretical foundation in Chemistry. He also developed his famous law of partial pressures, known as Dalton's law. -
Michael Faraday
Faraday made one of the most significant discoveries leading to the idea that atoms had an electrical component (electromagnetism). He placed two opposite electrodes in a solution of water containing a dissolved compound. His observations were that one of the elements of the dissolved compound accumulated on one electrode, while the other accumulated on the opposite electrode. This made it clear to Faraday that electrical forces were responsible for the joining of atoms in compounds. -
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William Crookes
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Henri Becquerel
Becquerel also discovered that the allegedly active substance in uranium (uranium X) lost its radioactivity in time, whereas [inactive & fresh] uranium eventually regained its radioactivity. This eventually led to the development of the transformation theory of radioactivity, explaining the phenomenon as a subatomic chemical change in which one element spontaneously transmutes into another. -
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J.J. Thomson
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Max Planck
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Hantaro Nagaoka
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Marie Curie
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Arnold Sommerfeld
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Ernest Rutherford
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William Crookes
Crookes played an important role in the atomic structure. He is also responsible for the reconstruction of the Cathode Ray and his discovery of the element thallium. His studies proved to be fundamental in the development of atomic physics. Crookes also discovered the principle of the Crookes radiometer, a device that converts light radiation into rotary motion. The principle has found multiple applications in the development of sensitive measuring instruments. -
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Lise Meitner
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Albert Einstein
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Niels Bohr
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Erwin Schrödinger
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James Chadwick
Chadwick's findings were pivotal to the discovery of nuclear fission and ultimately led to the development of the atomic bomb. -
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Louis De Broglie
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Satyendra Nath Bose
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Marie Curie
Marie Curie discovered the two elements (polonium and radium) alongside her husband while working with the mineral pitchblende, of which they were awarded the Nobel Prize. She also discovered radioactivity through uranium experiments and championed the development of X-rays after her husband's death. Her achievements, including her two Nobel Prizes and her position as a teacher in a male-exclusive school, inspired female scientists to surface in the sexist society of the past. -
Henri Becquerel
Becquerel was the French physicist to discover natural radioactivity through his investigations of uranium and other substances. He shared the Nobel Prize for Physics with Pierre and Marie Curie. He also measured the deflection of beta particles (a constituent of the radiation in both electric and magnetic fields) and discovered the physiological effects of radiation leading ultimately to medical use. -
Max Planck
Planck was the originator of the quantum theory of energy. His work greatly contributed to the understanding of atomic and subatomic processes. He came up with Planck's constant, an equation derived through the postulation of the idea that energy of light is proportional to the frequency. His theory accurately predicted the spectral density of electromagnetic radiation. His work also assisted Albert Einstein’s discovery of photons (light existing in discrete quanta of energy). -
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Wolfgang Pauli
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Werner Heisenberg
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Paul Dirac
He also developed a theory of "constrained quantization", which provided quantum field analysis of the vibrations of a membrane and proved extremely useful to modern practitioners of superstring theory and M-theory. -
JJ Thomson
Thomson discovered the electron, the negatively-charged particle in the atom, through his experimentations with cathodes ray tubes, and determined its fundamentality in an atom. He proposed his own diagram of the atomic structure, the plum pudding model of the atom, which had negative electrons on top as the “raisins” and the positive electrons contained in the “dough”. Although his theory was proven wrong later, his model introduced the notion that an atom consisted of charged particles. -
Hantaro Nagaoka
Hantaro Nagoaka developed the earliest published quasi-planetary model of the atom, known as the Saturnian system. Nagoaka assumed that the atom is a massive, positively-charged sphere encircled by many light-weight, negatively-charged electrons, bound by electrostatic forces, which is stabilized and attracted to the heavy planet by gravity. The atoms in his model were inherently unstable because the continuous radiation causes the electrons to gradually lose energy and spiral into the nucleus. -
Albert Einstein
Albert Einstein developed the special and general theories of relativity and the equation E=MC2. The equation states that the energy of a body (E) is equal to the mass (M) of that body times the speed of light squared (C2), suggesting that tiny particles of matter could be converted into huge amounts of energy. This will eventually to the development of atomic power, energy, and bomb. His general relativity also allowed for a more accurate prediction of planetary orbits around the sun. -
Ernest Rutherford
Rutherford came up with the nuclear atom/planetary model of the atom, also known as the Rutherford model, describing the structure of atoms as a positively charged core called a nucleus, in which nearly all the mass is concentrated, surrounded by the light, negative constituents called electrons (Similar to planets revolving around the sun). Rutherford's model supplanted Thomson's theory with his gold foil experiment where he demonstrated that the atom has a tiny, but heavy nucleus. -
Period: to
Chien Shiung Wu
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Niels Bohr
Bohr proposed a theory for hydrogen atoms basing on the quantum theory stating that energy is transferred only in certain well-defined quantities. Electrons should move around the nucleus, but only in prescribed orbits. Each orbit corresponds to a specific energy state, and when jumping from one orbit to another with lower energy, a light quantum is emitted. His theory explained why atoms emit light in fixed wavelengths. He also conducted a Nobel Prize-winning research on the structure of atoms. -
Satyendra Nath Bose
Satyendra discovered what became known as bosons and worked with Albert Einstein to define one fo two basic classes of subatomic particles. He is known for his work with Einstein on the Bose-Einstein condensate, for his work in developing a theory regarding the gaslike qualities of electromagnetic radiation. He worked on quantum physics and relativity and was able to derive Planck's constant to bring forward a solution leading to the development of Bose's statistics. -
Werner Heisenberg
Werner Heisenberg discovered a way to formulate quantum mechanics in terms of matrices. He is best known for the publishing of his uncertainty principle and he made significant contributions to the theories of the hydrodynamics of turbulent flows, the atomic nucleus, ferromagnetism, cosmic rays, and subatomic particles. He was also instrumental in planning the first West German nuclear reactor as well as the development of the atomic bomb (through the discovery of different forms of hydrogen). -
Wolfgang Pauli
Wolfgang Pauli is famous for his Pauli exclusion principle, which states that no two electrons can occupy the same quantum state at the same time in an atom. Pauli also significantly contributed to the fields of quantum mechanics, quantum field theory, and solid-state physics, and successfully hypothesized the existence of the neutrino. Pauli used Heisenberg's new matrix theory of quantum mechanics to find the observed spectrum of the hydrogen atom. -
Louis De Broglie
Louis is most famous for his groundbreaking work on quantum theory. He discovered the wave nature of electrons and suggested that all matter have wave properties. His theory resolved and explained a question brought up by the calculations of the electron's motion within the atom, offering an explanation for its restricted motion. Before the development of his theory, electrons were seen as only behaving like particles. Therefore, his discovery changed the viewpoints of electrons immensely. -
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Ronald James Gillespie
Gillespie also studied the shape of molecules and developed the widely used valence shell electron pair repulsion theory. This theory helps scientists describe and predict the shape of any molecule based on how many electron pairs exist in the outer shell. -
Erwin Schrödinger
Erwin Schrödinger contributed to the wave theory of matter and to other fundamentals of quantum mechanics. He discovered the quantum mechanical model of the atom, and came up with the Schrödinger's cat experiment which proved to be paradoxical. He introduced a theory describing the wave-like behavior of particles of matter by a wave equation known as the Schrödinger equation. The solution to his equation is wave functions that can only be related to the probable occurrence of physical events. -
Arnold Sommerfeld
Sommerfeld is known mostly for his work on atomic theory in the field of quantum mechanics and for mentoring more recipients of the Nobel Prize in Physics than any other physicists. His atomic model permitted the explanation of fine-structure spectral lines. From the Bohn model of the atom, he postulated the azimuthal quantum number and later he introduced the magnetic quantum number. His work also contributed to the study of thermoelectricity and metallic conduction. -
Period: to
Richard Bader
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James Chadwick
James Chadwick is famous for discovering the neutron by bombarding a beryllium atom with alpha particles which produced unknown radiation. Chadwick interpreted the radiation as being composed of particles with a neutral electrical charge and having the approximate mass of a proton. As a result of the neutral charge, the particle became known as the neutron. The bombardment of neutrons on the elements can succeed in penetrating and splitting the nuclei, generating an enormous amount of energy. -
Lise Meitner
Lise Meitner discovered that nuclear fission can produce a massive amount of energy (earning her the title "mother of the atomic bomb"), and she is famous for her work with radioactivity. Growing up, she was denied education due to her gender and was often looked down upon when working with male coworkers despite her brilliance to develop the first theoretical explanation of the fission process uranium undergoes. In 1917, Meitner also discovered a new isotope of protactinium alongside Hahn. -
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Robert J LeRoy
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Chien Shiung Wu
Chien helped develop the process for separating uranium metal into U-235 and U-238 isotopes by gaseous diffusion. She also developed an improved Geiger counter for measuring nuclear radiation levels. In 1956, she proved that identical nuclear particles do not always act alike by using radioactive cobalt at near absolute zero temperatures. She also made the first confirmation of Enrico Fermi's theory of beta decay. Unfortunately, she did not receive the acknowledgment she deserved for her works. -
Paul Dirac
Dirac made fundamental contributions to the development of quantum mechanics, quantum field theory, and quantum electrodynamics. He is known for his attempts to unify the theories of quantum mechanics and relativity theory. He formulated the Dirac Equation, describing the behavior of fermions like the electron, and predicted the existence of antimatter like positrons. -
Robert J LeRoy
Robert J LeRoy developed the Leroy-Bernstein theory alongside R.B.Bernstein and the derivation of the LeRoy Radius. Le Roy is the author of many computer programs that aid in collecting information from experiments. His works are used by schools and labs throughout the world and have contributed immensely to the progress of science. -
Ronald J. Gillespie
As Gillespie explored the chemistry behind the brightly colored solutions produced when certain elements were dissolved in concentrated sulfuric acid, he developed superacids like HSO3F, a widely used acid in chemistry. This development led to the production of non-metallic elements in the form of polyatomic cations, opening up a whole new field of chemistry. -
Richard Bader
Richard Bader is widely known for extending quantum mechanics to open systems, with his group's Quantum Theory of Atoms in Molecules. He discovered that electron density is very important in explaining the behavior of atoms in a molecule. His theory states that there are no atomic orbitals in the molecules. Although it was not very accepted in the beginning, it became more widely accepted after the publication of his book.
