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600 BCE
Acharya Kanad
Acharya Kanad thought of the atom as tiny objects that are invisible to the naked eye, and considered it indestructible or eternal. He also theorized that an atom has an inherent urge to combine with another atom. He also explained that combining two atoms belonging to the same class would create a binary molecule. -
400 BCE
Democritus
"by convention bitter, by convention sweet, but in reality atoms and void"
Democritus was a philosopher in Ancient Greece. He believed that the smallest possible piece of matter was indivisible. He named the smallest piece of matter “atomos,” meaning “not to be cut.” Democritus thought that atoms were small, hard particles that were made from the same material but were different shapes and sizes. -
300 BCE
Aristotle
Aristotle was a philosopher that declared that all matter was made up of four elements. Earth, fire, air, and water. He also said that matter only had four properties. Hot, cold, dry, and wet. -
Isaac Newton
Newton proposed a mechanical universe where small solid masses were in motion. Essentially, he believed that there were small masses that 'bounced' all around us. Newton was the one that began to understand that atoms are not stationary and move around. -
John Dalton
Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms. Dalton theorized that all matter is made of atoms. He declared that atoms are too small to see and are indestructible. All atoms of a given element are exactly alike and atoms of different elements are different. -
George Johnstone Stoney
Stoney's most important discovery was the calculation of the magnitude of the atom, which he coined as the "electron". He had calculated the magnitude of his electron from his data and the value obtained later became known as a coulomb. -
J.J. Tomson
Thomson provided the first hint that an atom is made of even smaller particles. He discovered the presence of a negative particle in the atom, which is the electron.Thomson's theory was that atoms are a positively charged substance with negatively charged electrons scattered around in it. -
Max Planck
Planck was able to deduce the relationship between the energy and the frequency of radiation. This was based on the revolutionary idea that the energy emitted by a resonator could only take on discrete values or quanta. This explained the reason of hot glowing matter. -
Hantaro Nagaoka
Nagaoka believed that the atom is a large, positively charged sphere, encircled by many light-weight, negatively charged electrons, bound by electrostatic forces similar to Saturn's ring. This model is called the saturnian model. -
Albert Einstein
Einstein is best known for his theory of relativity and the equation E=MC2. This equation stated that under the right conditions, matter can become energy and energy can become matter. This led to the production of atomic bombs. -
Ernest Rutherford
Rutherford performed an experiment called the gold foil experiment. It consisted of shooting positively charged particles into extremely thin gold foil and seeing where on the surrounding circular wall it hit. Rutherford believed that the particles would all go straight through the atom, however, a very small amount went either off to the sides or back towards the positive particle stream. This led to him discovering something inside of the atom, the nucleus. -
Niels Bohr
Bohr built on the concept that the mass of an atom is contained mostly in the nucleus. He also theorized that electrons move in definite orbits around the nucleus, similar to how planets circle the sun. -
Francis William Aston
Aston built his own mass spectrograph and made improvements to it which made his machine have improved mass resolving power and mass accuracy. This led to him identifying 212 naturally occurring isotopes. -
Louis de Broglie
Broglie built off of the fact that Einstein introduced photons in light waves. He knew that light contains particles which are concentrations of energy incorporated into a wave. This suggests that all particles, like the electron, must be transported by a wave into which it is incorporated. This is known as the wave-particle duality. -
Werner Heisenberg
Heisenberg is best known for his uncertainty principle. The uncertainty principle states that a particle's position and momentum cannot both be known exactly. -
Wolfgang Pauli
Pauli was able to formulate a new principle which he called the Pauli Principle. It stated that no two electrons in an atom could have identical sets of quantum numbers. -
Erwin Schrödinger
Schrödinger used a mathematical equation to describe the odds of finding the location of an electron on different layers, which are called orbitals. These orbitals could be described as "electron density clouds". -
James Chadwick
Chadwick used alpha particles to discover a neutral atomic particle with a mass close to a proton. They differed from alpha rays because they repelled considerable electrical forces that are in the nucleus of many heavy atoms. This was discovered as the neutron. -
Dorothy Crowfoot Hodgkin
Hodgkin used X-ray crystallography to determine the three-dimensional structure of several complex organic molecules. This was important to learning how living organisms function. -
Rosalind Franklin
Franklin worked with machine tools and later moved onto x-ray crystallography to classify coals and predict their performance as fuels. Her discoveries related to the molecular structure of coal and carbon were used to develop strong carbon fibers and slow reactions in nuclear power plants. -
Robert J Leroy
Leroy is known for the development of the Leroy-Bernstein theory. He understood and explained how properties of molecular systems are the results of forces of interaction. He used quantum mechanics and computer models to define and analyze the basic forces between atoms and molecules. -
Richard F.W. Bader
Bader found that when explaining the behaviour of atoms, the electron density is very important. He went against the accepted theories that already exist and believes that there are no orbitals in molecules.
