A timeline of the history of atomic theory.
History of Atomic Theory Timeline
Brooke BrayLeslie LockettChemistry- 8thDecember 2, 2010
DemocritusContribution, year of contribution, how it was made:Democritus expanded the atomic theory of Leucippus. He maintained the impossibility of dividing thingsad infinitum. From the difficulty of assigning a beginning of time, he argued the eternity of existing nature, of void space, and of motion. He supposed the atoms, which are originally similar, to be impenetrable and have a density proportionate to their volume. All motions are the result of active and passive affection. He drew a distinction between primary motion and its secondary effects, that is, impulse and reaction. This is the basis of the law of necessity, by which all things in nature are ruled. Maintaining his atomic theory throughout, Democritus introduced the hypothesis of images or idols (eidola), a kind of emanation from external objects, which make an impression on our senses, and from the influence of which he deduced sensation (aesthesis) and thought (noesis). He distinguished between a rude, imperfect, and therefore false perception and a true one. In the same manner, consistent with this theory, he accounted for the popular notions of Deity; partly through our incapacity to understand fully the phenomena of which we are witnesses, and partly from the impressions communicated by certain beings (eidola) of enormous stature and resembling the human figure which inhabit the air. He carried his theory into practical philosophy also, laying down that happiness consisted in an even temperament. From this he deduced his moral principles and prudential maxims. His year of contribution was 450.
Interesting fact:His father was from a noble family and of great wealth, and contributed largely towards the entertainment of the army of Xerxes on his return to Asia. As a reward for this service the Persian monarch gave and other Abderites presents and left among them several Magi. Democritus, according to Diogenes Laertius, was instructed by these Magi in astronomy and theology.
Contribution, year of contribution, how it was made:John Dalton calculated atomic weights from percentage compositions of compounds, using an arbitrary system to determine the likely atomic structure of each compound. If there are two elements that can combine, their combinations will occur in a set sequence. The first compound will have one atom of A and one of B; the next, one atom of A and two atoms of B; the next, two atoms of A and one of B; and so on. Hence, water is HO. He believed that different gases had different volumes, and surrounds of caloric, which explains why mixed gases stay in constant motion. Dalton consolidated his theories in his New System of Chemical Philosophy (18081827).
Interesting fact:Although he led a modest life, Dalton had over 40.000 people walk at his funeral.
Contribution, year of contribution, how it was made:Mendeleev's arranged the 63 known elements into a Periodic Table based on atomic mass, which he published in Principles of Chemistry in 1869. His first Periodic Table was arranged the elements in ascending order of atomic weight and grouping them by similarity of properties. He left space for new elements, and predicted three yet-to-be-discovered elements. Mendeleev's table did not include noble gases, because they were not discovered yet. The original table has been modified and corrected several times, by Henry Moseley.
Downfall of contribution:Henry Mosely corrected Dimitri Mendeleev's periodic table many times. But for the most part Mendeleev was pretty accurate.
Interesting fact:Mendeleev lived to be 73, which is pretty old in those days.
Contribution, year of contribution, how it was made:Robert Bunsen perfected the Bunsen burner. It was made earlier by Michael Faraday, but Bunsen perfected it and then it was named after him. He was also able to produce pure metals by electrolysis. Bunsen discovered the best known antidote to arsenic poison. All was almost cut short when he almost lost an eye from a sliver of glass, and got arsenic poisoning. He perfected the Bunsen Burner in the year 1885.
Interesting fact:One of Robert Bunsen's hobbies was geology.
Contribution, year of contribution, how it was made:He investigated electrical discharges through gases at low pressures. He discovered canal rays and gave cathode rays their name. In 1876 Goldstein demonstrated that cathode rays can cast shadows and that the rays are emitted perpendicular to the cathode surface. He then showed how cathode rays could be deflected by magnetic fields. In an experiment 1886, he perforated the anode and observed glowing yellow streamers emanating from the perforations. He termed them Kanalstrahlen or canal rays. Goldstein later investigated the wavelengths of light emitted by metals and oxides when canal rays impinge on them, and observed that alkali metals show bright spectral lines. His creation was known as the Raisin Pudding Model of the Atom. When the cathode of a cathode-ray tube was perforated, Goldstein observed rays he called "canal rays," which passed through the holes, or channels, in the cathode to strike the glass walls of the tube at the end near the cathode. Since these canal rays travel in the opposite direction from the cathode rays, they must carry the opposite charge.
Interesting fact:In 1908, Goldstein won the Hughes Medal for an original discovery in the physical sciences, particularly electricity and magnetism or their applications.
Contribution, year of contribution, how it was made:Stoney's most important scientific work was the calculation of the magnitude in the atom/ particle of electricity. Term he gave name to the electron. He also studied the nature of the sun. He also gave kinetic theory of gases to the planetary atmospheres. That study had important implications for the other worlds. He also proposed explanations for the escape of hydrogen and helium from the field of Earths gravity and the absence of atmosphere on moons. He introduced the use of wave numbers into spectroscopy. Stoney retired to London in 1893 and became vice president of the Royal Society in 1898. His work in the field of university administration is noticed by the Stoney Summer School, which investigates matters of science policy and government. He also got a Diploma in Civil Engineering in 1850 at Trinity College. He designed a dredging plant and rebuilt nearly 7,000ft of quay walls along the north, south banks of the River Liffey. He coined the term "electron" in 1891.
Interesting fact:For many years George Stoney took an important part in the educational development of his country as a Secretary of the Queen's University of Ireland.
Contribution, year of contribution, how it was made:Thomson's discovery of the electron began in 1895 with a series of experiments in the Cavendish Laboratory. Influenced by the work of James Clerk Maxwell land the discovery of the X-ray, Thomson deduced that cathode rays exhibited a single charge-to-mass ratio e m and must be composed of a single type of negatively charged particle, which he called "corpuscles." G. Johnstone Stoney had proposed the term electron earlier as a fixed quantum of electric charge in electrochemistry, but Thomson realized that it was also a subatomic particle, the first one to be discovered. After further experiments on how cathode rays penetrate gases, Thomson hypothesized that "we have in the cathode rays matter in a new state this matter being the substance from which all the chemical elements are built up." Thomson might be described as "the man who first split the atom," and to a great extent, he made atom physics a modern science.
Interesting fact:He was awarded the Nobel Prize in Physics in 1906 and was knighted in 1908. His investigations into the action of electrostatic and magnetic fields in the nature of so-called "anode rays" or "canal rays" would eventually result in the invention of the mass spectrometer by Francis Aston, a tool that allows the determination of the mass-to-charge ratio of ions and which has since become an ubiquitous research tool in chemistry.
Contribution, year of contribution, how it was made:Planck is known as the Originator of Quantum Theory. He proposed the quantum of action, which is known as Planck's Constant. This explained the pattern of light intensity emitted a black body at any given frequency. He came out with a paper in 1900 that formed a baseline for a new field of physics called quantum mechanics.
Interesting fact:His son was involved with a plan to assassinate Hitler.
Contribution, year of contribution, how it was made:Marie Curie basically discovered radioactivity. She led the pioneering research into this topic, and also coined the term radioactivity. She also discovered two elements, and discovered how to extract pure radium salts from metal. The majority of her accomplishments happened in 1901.
Interesting fact:Marie Curie died on the 4th of July.
Contribution, year of contribution, how it was made:He is remembered for Abegg's rule (partially anticipated by Dmitri Mendeleev), which states that each element has two valences: a normal valence and a contravalence, the sum of which is eight. He discovered the theory of freezing-point depression and anticipated Gilbert Newton Lewis' octet rule by pointing out that the lowest and highest oxidation states of elements often differ by eight. He researched many topics in physical chemistry, including freezing points, the dielectric constant of ice, osmotic pressures, oxidation potentials, and complex ions. Abegg is best known for his research recognizing the role that valence played in chemical interactions. He found that some elements were less likely to combine into molecules, and from this concluded that the more stable elements had what are now called full electron shells. He was able to explain the attraction of atoms through opposite electrical charges. He also made the distinction between normal valence and contravalence. He found that the sum of these two valences always comes to eight, a rule that is now known as Abegg's rule.
Interesting fact:His favorite pastimes were traveling, ballooning, skiing and taking photographs.
Contribution, year of contribution, how it was made:Soddy said that the same elements exist in different forms, which means the nuclei had the same number of protons but different numbers of neutrons. This describes isotopes. His theory stated that different elements can be chemically indistinguishable, but have different characteristics and atomic weights. He proposed this in 1912. in 1903 he helped introduce the concept of half-life.
Interesting fact:He worked with James Chadwick and Ernest Rutherford.
Contribution, year of contribution, how it was made:What didn't Einstein do? In 1905 he came up with the theory of relativity. Much of his work was too scientific for most people outside of the chemistry and physics world to understand, but he did a lot in both of those worlds. He is the most famous scientist of all time.
Interesting fact:Einstein's brain was preserved after he died.
Contribution, year of contribution, how it was made:Rutherford was one of the first to study radioactivity, he increased peoples understanding of the atom, coined the terms alpha ray, beta ray, and gamma ray, half-life (radioactive decay), and was popular for being the first scientist to split an atom. He worked with many, MANY famous scientists. Rutherford showed that x-rays cause air particles to split into ions in the year 1896. He also concluded that the nucleus of an atom is small and dense and electrons orbit around it in the year 1911.
Interesting fact:He is called the Father of Nuclear Physics
Contribution, year of contribution, how it was made:Neils Bohr studied under both J.J. Thomson and Ernest Rutherford. While working under Rutherford, Bohr expanded Rutherford's work into a new theory on the structure of an atom. He is most famously known for the Bohr Model, which is a model of an atomic. Bohr said that electrons travel in fixed orbitals around the atoms nucleus. He also explained how electrons absorb and emit energy. Bohr also said that the outer orbitals hold more electrons than inner orbitals.
Interesting fact:He died of a stroke.
Contribution, year of contribution, how it was made:In 1913 Moseley introduced Moseley's Law, which stressed the importance of the atomic number. He made it a point that the atomic number is more important than the atomic weight. He also predicted the existence of two elements.
Interesting fact:Henry Moseley was killed in war.
Contribution, year of contribution, how it was made:Schrodinger introduced the electron cloud to the chemistry world. This happened in the year 1926. He came up with a mathematical equation for the way that electrons moved in waves inside of the hydrogen atom. He also introduced Schrodinger's Cat, which is a paradox.
Interesting fact:He was Roman Catholic.
Contribution, year of contribution, how it was made:Hund did a lot of work on the structures of atoms and molecules, along with the orbital theory that was named after him and his partner, Robert Mulliken. It is known at the Hund-Mulliken theory. This happened in the year 1927.
Interesting fact: He has the same birthday as Brooke's older sister.
Contribution, year of contribution, how it was made:As a scientist, Millikan made numerous momentous discoveries, chiefly in the fields of electricity, optics, and molecular physics. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity. Next, he verified experimentally Einstein's all-important photoelectric equation, and made the first direct photoelectric determination of Planck's constant h (1912-1915). In addition his studies of the Brownian movements in gases put an end to all opposition to the atomic and kinetic theories of matter. During 1920-1923, Millikan occupied himself with work concerning the hot-spark spectroscopy of the elements (which explored the region of the spectrum between the ultraviolet and X-radiation), thereby extending the ultraviolet spectrum downwards far beyond the then known limit. The discovery of his law of motion of a particle falling towards the earth after entering the earth's atmosphere, together with his other investigations on electrical phenomena, ultimately led him to his significant studies of...