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500 BCE
Leucippus of Miletus
Leucippus introduced the idea of atomism, the idea that everything is made up of tiny indivisible building blocks. This became the entire atomic theory. -
350 BCE
Democritus of Abdera
Democritus picked up the ideas of Leucippus, adding onto it to create his own atomic theory. He added the following:
- Atoms are physically indivisible and indestructible
- There is always space between atoms
- Atoms are always in motion
- There are infinite kinds of atoms and atoms
This became the first set of rules for the atomic theory. -
340 BCE
Empedocles of Acragas
Empedocles proposed that all substance is made of pure elements, fire, air, water and earth. This was a completely different idea than what Leucippus proposed, and was a whole new theory. -
Period: 300 BCE to
Study of Alchemy
When Aristotle adopted the 4 substance idea (earth, fire, air and water), he guessed that you can change these elements through different chemical reactions. This spawned the practice of alchemy. Because the first man to discover how to turn other metals into gold would be wealthy, many people took up alchemy. Although some people see this as a waste because they found no gold, they furthered their knowledge of general chemistry such as metallurgy and chemical reactions. -
Antoine Lavoisier
Antoine Lavoisier was a French chemist. His most notable discovery was what we now know today as the Law of Conservation Mass. He discovered that all mass is conserved in a reaction, no atoms are created or destroyed in the reaction. -
Joseph Proust
Joseph Proust was a French chemist who discovered that every single chemical compound had the same ratio of elements (as long as it is the same compound, for example any water molecule has the same ratio of hydrogen to oxygen). This is now known as the Law of Definite Proportions. -
John Dalton
John Dalton was an English chemist, physicist, and meteorologist. He believed that elements were each composed of their own unique type of atom that cannot be altered or destroyed by chemical means, and they can combine with other atoms to form new complex chemical structures. Because he was the first person to propose a theory based on his experiments, this was the first truly scientific atomic theory. -
Max Planck
Max Planck was a German theoretical physicist. He devised Planck's law, which states that energy is discreetly emitted by black-bodies in the form of quanta that is directly proportional to the radiation being absorbed by the black body. This opened up an entire new field of study, now known as Quantum Mechanics. His discoveries meant that the laws of classical mechanics do not apply to subatomic particles. -
Marie Curie
Marie Curie was a French physicist. Aside from her pioneering work on radioactivity, she isolated and discovered polonium AND radium, even though she was a woman (sexism was blatant) -
J.J. Thomson
J.J. Thomson was an English Physicist. His experiments involving cathode ray tubes proved that every element had atoms containing tiny negative subatomic particles we now know today as electrons (in 1897). In sight of this discovery, he created a new atomic model, called the Plum Pudding Model, consisting of a circular positive atom with tiny negative electrons sprinkled throughout the positive atom. -
Hantaro Nagaoka
Hantaro Nagaoka was a Japanese physicist. He proposed a new planetary model of the atom, with a very large nucleus and orbiting electrons like the rings of Saturn. -
Albert Einstein
Albert Einstein is without a doubt the most famous person who ever lived. He developed the E=mc^2, which means that the energy released by mass is equal to the mass times the speed of light squared. Our understanding of the atomic theory was now solid enough to begin imagining atomic bombs (sort of)! -
Ernest Rutherford
Rutherford was a British physicist. His experiments involving shooting alpha particle beams at thin metal foil and measuring how it scatters. Instead of bouncing off, the vast majority of alpha particles went through, and a very small amount bounced off. This meant atoms were mostly empty space, and that most of the mass was in one spot. The discovery of the nucleus prompted the Rutherford Model, with a positive nucleus in the middle and negative electrons orbiting. -
Niels Bohr
Niels Bohr was a Danish physicist. He was the first to discover that electrons travel in separate orbits of different energy levels, and that the number of valence electrons determines the chemical properties of the atom. This led to the Bohr-Rutherford model, consisting of a dense nucleus with orbiting electrons. -
Homer Burton Adkins
Homer Burton Adkins was an American chemist who was regarded as a world authority on the hydrogenation of organic compounds. His research increased our knowledge of hydrogenation, which is used all over the world to reduce or saturate organic compounds. -
Louis de Broglie
Louis de Broglie was a French physicist. In his PhD thesis, he theorized that the particle-wave duality existed for all matter. The idea of particle-wave duality existed since 1803, originating from the famous Double-Slit Experiment. He also proved that the wavelength was inversely proportional to its size, and it is only relevant with tiny subatomic particles. This meant that atoms exhibit wave behavior. -
Wolfgang Pauli
Wolfgang Pauli was an Austrian-Swiss-American physicist. He devised the Pauli Exclusion Principal, which says that no two electrons in an atom can have the same quantum numbers. It was later discovered this principal also applies for protons and neutrons. Quantum numbers describe the state of a subatomic particle including its spin, orientation, orbital, etc. -
Erwin Schrödinger
Erwin Schrödinger was an Austrian physicist. He created the Electron Cloud Model, consisting of a dense nucleus and a "cloud" of electrons with a higher chance of finding one in a certain spot than another. This was groundbreaking, as it essentially meant that a single electron is dispersed throughout the entire cloud. The electron is in "superposition". This likely led him to challenge the Copenhagen Interpretation by devising the Schrodinger Cat experiment, where a cat is in superposition. -
Werner Heisenberg
Werner Heisenberg was a German physicist. He created the Heisenberg Uncertainty Principal, which states that the position and velocity of an object can never be perfectly measured at the same time, building off of Schrodinger's atom model with the electron cloud. -
James Chadwick
James Chadwick was a British physicist. He discovered neutrons by bombarding Beryllium with alpha particles, which released neutrons in the form of radiation. -
C. V. Raman
C. V. Raman was an Indian physicist. He did some ground-breaking work in the field of light scattering, discovering that when light passes through a transparent object, some of the deflected light changes wavelength AND amplitude. This effect is now known as Raman scattering, and it advanced our knowledge on how light behaves and particle-wave duality. -
Gerty Cori
Gerty Cori was an American biochemist. She discovered glycogen metabolism, which is a readily mobilized storage form of glucose. Glycogen metabolism is a very important part of homeostasis, which allows all humans and animals to survive. -
Rudolph Marcus
Rudolph Marcus is a Canadian chemist. He created the Marcus theory, which gives thermodynamic and kinetic framework for electron transfer. It is essentially the rate of which electrons can transfer. This aids our understanding of how bonding occurs. -
John Polanyi
John Polanyi is a Canadian chemist. He made some of the first discoveries on chemiluminescence, and then developed the technique of infrared chemiluminescence. This was used to measure weak infrared emissions from newly formed molecules so they could examine energy disposal during a reaction, and now we know what energy looks like during a reaction. -
Gerhard Herzberg
Gerhard Herzberg was a Canadian chemist. His main accomplishments revolved around atomic and molecular spectroscopy. He has determined the structures of many diatomic and polyatomic molecules, that are very difficult to determine the structures of, like free methyl. He also uses his methods to identify molecules in the atmosphere, interstellar space, and comets. -
Stephanie Kwolek
Stephanie Kwolek was an American chemist, best known for inventing Kevlar, a very heavily used tough fabric sold around the world. She also discovered the first family of synthetic fibers of crazy strength and toughness, poly-paraphenylene terephtalamide. She created the field of polymer chemistry, and her discoveries help protect our equipment and our soldier's lives.
