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4000 BCE
Alchemy
Alchemy was the quest to understand the chemical properties of the world around us. Alchemy was scientific but also was known for its deep roots in spiritual tradition. Though they led to large advancements in chemical industry’s such as basic metallurgy and metalworking. Alchemy was also focused heavily on the purifying of elements, this led to the discovery of different physical and chemical properties of elements. -
460 BCE
Democritus
Proposed the earliest views on atoms. They hypothesized that everything was made of “atoms” and that they are physically, but not geometrically, indivisible. As well as between atoms lies empty space and atoms will always be in motion. -
John Dalton
Dalton introduced his theory based on the law of conservation of mass and the law of constant composition. He believed all matter is made of atoms and atoms are solid, massy, hard, impenetrable, movable particles. He also introduced new ideas on all atoms in an element having identical properties as well as chemical reactions rearranging atoms rather than destroying or creating them. -
J.J. Thomson
Building off Dalton's theory's Thomson used cathode ray tubes to determine property's of atoms. In this process he discovered a particle with a smaller mass than an atom and a negative charge, these are now known as electrons. He theorized that all particles have a neutral charge so the atoms had to have some source of positive charge to balance the negative charge of the electrons. This led to the creation of the plum pudding model of the atom where electrons are floating in a positive soup. -
Marie Sklodowska Curie
Curie came from a very scientific family and was a leader in the field of radiation. Using an electromagnet she discovered that uranium rays caused the air around a sample to conduct electricity. She hypothesized that the radiation came from the atom rather than interaction between molecules. She also discovered that Thorium is also radioactive. -
Max Planck
He explained how energy is radiated in packets rather than an unbroken wave. These packets are called quanta and he is able to determine the exact energy level of each quantum. The energy level is calculated by taking the frequency of the radiation multiplied by the universal constant, this is now known as Planck's constant. -
Hantaro Nagaoka
Nagaoka rejected Thomson's plum pudding model and theorized instead a planetary model. He believe that an atom had a large atomic center and electrons orbiting the nucleus bound by electromagnetic forces. This model was call the planetary model. In 1908 he abandoned his proposed model. -
Albert Einstein
Einstein sought to harmonize the laws of mechanics and the laws of electromagnetic field. He also proposed the theory of gravitation and published the general theory of relativity in 1916. He was also able to calculate the average distance a particle would move in a liquid using Brownian motion. -
Ernest Rutherford
In Rutherford's famous gold foil experiment he shot Alpha particles through a sheet of gold. He noticed that 1/20000 particles where shoot back at him. This led him to believe that most of the atom is empty space and the positive charge is centralized with most of the mass of the atom (nucleus). These discovers led to the creation of the atomic model of the atom. -
Niels Bohr
Bohr quantization of electronic structure suggested that there are certain fixed radius's that electrons must orbit around. He created equations to find the smallest atomic radius possible for hydrogen. Though his theory only worked on atoms that had 1 electron, it was unable to explain more complicated atoms. -
Louis de Broglie
de Broglie created an equation about matter and wave-particle duality that set the ground work for wave mechanics. This equation let you calculate wave length using Planck's constant, momentum, rest mass, velocity and the speed of light. -
Satyendra Nath Bose
Bose was seminal in the creation of quantum statistics, he derived Planck's quantum radiation law by using a novel way to counting states using identical particles. Though it was not published immediately, Bose sent it to Einstein where he published it on Bose's behalf in Germany. He worked with Einstein and discovered the Bose–Einstein condensate which is a dense collection of boson's. -
Werner Heisenberg
Heisenberg was a leading member of the German atomic program during WW2. He was approached by the Nazi's to turn this knowledge into a weapon and Heisenberg believed that he could create a bomb before 1945. 1942 they realized their research was better placed in more pressing matters. He is famous for his uncertainty principle and theory of quantum mechanics. -
Wolfgang Pauli
Pauli was involved with the creation of quantum mechanics. He introduced a new quantum number, this number would later be known as spin. He also concluded that if a quantum state was occupied by one electron all other electrons are excluded from that state, this is now known as the exclusion principle. -
Erwin Schrödinger
Schrödinger theorized that electrons withing atoms can be explained mathematically as matter waves. He also created an equation the gives wavelengths for an atom. Due to the Heisenberg uncertainty principle it is impossible to the position and energy of a specific electron. -
James Chadwick
In 1932 Chadwick discovered the neutron. He did this by sending alpha particles at beryllium atoms. He noticed that a new type of radiation was being given off. He believed that this radiation was composed of particles with a neutral charge, these particles are now known as Neutrons and have a similar mass to Protons. Now a more accurate model of atoms where created. -
Irène Joliot-Curie
Joliot-Curie discovered the existence of the proton and the neutron but failed to realize their significance. In 1933 she discovered the weight of a neutron. In 1943 also found a way to transform stable elements into radioactive isotopes using beta decay. Radioactive chemicals where important to modern medicine and this easy way to synthase them made this process much easier. -
Robert J. LeRoy
LeRoy used quantum mechanical theory to show how property's of molecular systems are influenced by the forced of interaction between particles. He used computer models to show how forces interacted between atoms and molecules. He discovered a radius for small molecule where inside the radius intra-molecular force is important and outside where inter-molecular forces take over. He also helped create software that lets experimental data be transformed into useful data. -
Ronald Gillespie
Gillespie has worked on the idea of valence shell electron pair repulsion. This theory states that you can predict the geometry of individual molecules from the number of electron pair surrounding an atom. The molecules will adapt an arrangement that will minimizes repulsion, giving us their geometry.
