The atomic theory originated in 442 BC. Democritus along with his teacher Leucippus proposed that all matter is composed of indivisible elements, Atomos. However, this proposal lacked evidence. On the other hand, Aristotle believed that everything was made of 5 particles–earth, water, fire, air, and ether. His theory was incorrect but widely accepted for about 2000 years.
1700-1803
In 1700, Lavoisier and Paulze found out that elements are the primary constituents of matter that cannot be broken down through normal chemical reactions. In 1704, Newton proposed a mechanical universe where small solid masses were “swimming” everywhere, first to believe that particles aren’t stationary. In 1803, Dalton developed a theory with 5 parts: all matter is composed of atoms, atoms cannot be created or destroyed, all atoms of the same element are identical, chemical reactions occur when atoms are rearranged, and that compounds are formed by combing two or more types of atoms.
1831-1874
In 1831, Faraday experimented and concluded that forces joined atoms together and that atoms have an electrical component. In 1862, Plucker joined with Hittorf in investigating cathode rays. He pointed out that the same element under different temperatures may show different spectra. In the same year, Maxwell extended Faraday, Reimann, and Gauss’s theories, using Maxwell’s Equations to propose that light is an electromagnetic wave.
In 1869, Mendeleev organized elements into rows according to the elements’ atomic mass, and columns according to their properties, contributing to the periodic table. In 1874, Stoney estimated the properties of molecules in a volume of gas under standard conditions, yet the number of atoms in a gram of hydrogen was wrongly estimated.
1879-1900
In 1879, Crookes conducted an experiment to find out that particles are smaller than atoms or molecules. In 1886, Goldstein discovered canal rays, which are beams of positively charged ions. In 1895, Roentgen discovered rays that created images on photographic plates, now known as x-rays. In 1896, Becquerel discovered radioactivity in uranium, showing that an atom cannot be divided, meaning that the atom could change form and emit energy.
In 1898, Thomson discovered that an atom in fact can be divided, by working with the cathode ray tube. In addition, he used a magnetic field to conclude that the particles were negatively charged. In the same year, the Curies discovered polonium and radium. In 1899, Abegg concluded that there are 8 electrons in the outer group of an atom. In 1900, Planck proposed that energy is radiated every minute inset values, a quantum, using Planck’s constant.
1903-1916
In 1903, the Curies and Becquerel discovered radiation and radioactivity, winning the Nobel prize for physics. In 1905, Einstein hypothesized about the particle nature of light, generating the theories of relativity. In 1908, Geiger introduced the Geiger counter to measure radiation. In 1909, through his experiment, Rutherford believed that there is a big particle in the atom’s center that is positively charged and that the electrons are actually circling around the atom. In 1910, Millikan conducted his famous experiment, proving that atoms can be further broken down.
In 1913, Bohr found that electrons can move up an energy level if they are given a quantum of energy and that electrons travel around the atom in discrete energy levels. Also in 1913, Soddy worked with Rutherford in finding isotopes that may exist in different atomic weight forms. In 1916, Millikan verified Einstein’s equation for the photoelectric effect and found the exact value of Planck’s constant.
1925-1940
In 1925, Heisenberg discovered the uncertain principle of quantum mechanics. In 1926, Schrodinger developed the quantum mechanical model of the atom. In 1927, Broglie showed that atoms have wave-like characteristics. In 1928, Geiger introduced the Geiger-Muller counter. In 1932, Chadwick discovered neutrons located at the center of the atom that is neutrally charged. In 1938, Hahn discovered that nuclear fission produces large amounts of energy, and Seaborg discovered iodine, cobalt with Livingood, and technetium with Segre. In 1940, 1941, 1944, 1949, Seaborg discovered neptunium, plutonium, curium, americium, and berkelium.
By The Nine Eves
The Anonymous Helpers (TAH)