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360 BCE
Atomos by Democritus (460 - 370 B.C.)
Introduced the idea that all matter is made up of indivisible tiny pieces of pure substances that are surrounded by empty space, he called the small particles "atomos." He believed different kinds of matter consisted of different types or arrangments of atoms. -
340 BCE
The Four Elements by Aristotle (384 - 322 B.C.)
Proposed that all matter was made up of ratios of four elements: Air, Earth, Fire, Water. He believed these elements are in balance. And that the ratios affected the properties of matter, which suggests that some substances were compounds of substances. -
Period: 1220 to 1292
Experiments with Gunpowder by Roger Bacon (1220-1292)
Bacon experimented with gunpowder and its explosive properties and formula. Discovered gunpowder for himself when he set a mixture of charcoal, sulfur and saltpeter on fire, in which it exploded. Sometimes referred as the European father of gunpowder b/c hw was the first European to research and dive deeper into gunpowder ingredients and first in Europe to record its formula, which he wrote in his most important work, Opus Majus, in 1266-1267 for the Pope. -
Novum Organum by Sir Francis Bacon (1561-1626)
In his philosophical manifesto, Novum Organum (published in 1620), Bacon proposed Inductive logic be preferred for naturalistic study because deductive logic relied on syllogism (absolute conclusions) had fallacies that slowed progress. While inductive logic makes most probable conclusions based on incomplete evidence; evidence from experiments could build on the conclusion, making it stronger (constantly reforming hypothese). -
"The Skeptical Chymist" by Robert Boyle (1627-1691)
In "The Skeptical Chymist" (published in 1661), Boyle proposed that there are more than 4 elements, however, not to abandon the elements, but rather reevaulate the elements and expand on it, to redfined the "elements" to be "simple or perfectly unmingled bodies" because he argued Aristotle's elements were actually compounds and that the unmixed elements should be counted as the elements. Boyle valued admitting doubt so that experiments could be designed and tested. -
"The Father of Chemistry," Antoine Lavoisier (1743 - 1794)
Referred as the "Father of Modern Chemistry" b/c he revolutionized science by asking chemists share their data with each other so that the future generations can build on Chemistry. Published the first Chemistry textbook. And from his liquid and red calx mercury experiment, he discovered air isn’t an element and it actually contains many elemental gases and also discover oxygen. He also proposed the Law of Conversation of Mass, where matter is never created or destroyed, but moved around only. -
Period: to
Combustion Analysis by Lavoisier, Liebig, and others
Developed complicated methods to determine the amount of carbon, oxygen, and nitrogen in organic chemical compounds, since most flammable substances are organic. Most methods involved combustion and depended on the law of conservation of mass. Compounds that are made up of carbon, hydrogen, oxygen burns to give proportional amounts of CO2 and H2O. By trapping CO2 and H2O, chemists could determine ratios of elements in the compound. -
Law of Definite Proportions Proposed by Joseph Proust (1754-1826)
1794: Published Law of Definite Proportions (Law of Constant Composition or Proust's law); a compound is composed of exact proportions of elements by mass regardless of how compound was created. Used copper carbonate, two tin oxides and two iron sulfides to prove law by making artificial copper carbonate & comparing it to natural copper carbonate; each had same proportion of weights of 3 elements (Cu, C, O).
Also showed no intermediate compounds exist between two types of other compounds. -
The First Chemical Battery by Alessandro Volta (1745 - 1827)
Invented the voltaic pile or cell, which was one of the first electric batteries. It was a stack of alternating metal discs, consists of two metals copper & zinc, separated by brine-soaked cardboard that helped make them conductive. This invention was one of the first reliable continuous and reproducible sources of electricity, an important step in the study of electromagnetism and development or electrical equipment. A volt is a measure of electrical potential. -
Dalton's Atomic Theory by John Dalton (1766 - 1844)
Made the first atomic theory where he combined both ideas of elements and atomos, to get atoms
Dalton's Atomic Theory:
- All matter is made up of atoms that cannot be subdivided, created, or destroyed
- Atoms of a given element are identical in both properties
- Atoms of different elements differ in both properties and combine in simple, whole-number ratios to form compounds
- In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed. -
The First Periodic Table by Dimitri Mendeleev (1834 - 1907)
Made the first periodic table; put together all info on elements that had been discovered, and found periodic trends when he arranged them by relative mass, which he used as his primary sort. The secondary sort were affinity, reactivity, and physical properties. -
Canals Rays by Eugen Goldstein (1850 - 1930)
Experimented with a Crooks tube and discovered that perforated cathodes also had another beam, canal rays (+), that travelled in the opposite direction of the anode. It was known the beam, cathode rays (-), travelled from the cathode toward the anode. He also discovered that the mass-to-charge ratio of all elements was smallest for Hydrogen. Goldstein concluded atoms have positively charged and negatively charged potential. -
Period: to
Discovery of Radioactivity by Henri Becquerel (1852-1908), Marie Curie (1867 - 1934), and Pierre Curie (1859 - 1906)
1896: Henri found radioactivity; potassium uranyl sulfate images were strong/vivid without sunlight, proved uranium emit radiation without external energy source. Different radioactive substances in magnetic field, did/didn't deflected, 3 classes of radioactivity: negative, positive, electrically neutral. 1902: Curies extracted uranium from ore; leftover ore had more activity than pure uranium. Concluded the ore contained other radioactive elements, led to findings of polonium & radium. -
The Finding of Electrons by J.J. Thompson (1856 - 1940)
Discovered the subatomic particle, electron when found charge of cathode ray in the cathode ray tube was negative and equal in magnitude to a hydrogen ion charge. Its mass was smaller than even smallest atom, every element gave same result, proving Dalton's theory wrong, atoms could be subdivided. Proposed protons must be in atoms to make them neutral and make up the majority mass of atom. Made the plum pudding model where electrons and protons were raisins of the atom, the pudding. -
The Charge of an Electron by Robert Millikan (1868 - 1953)
Devised a special apparatus to suspend small oil drops between two electrical metal plates, where the drops feel according to gravity when the plates were off, allowing him to calculate their mass. Then charge needed to suspend the drops could be determined and compared to the mass of drops. The mass of charged particle had been determined and thus could determine charge per mass of one electron. He concluded the charge of one electron was 1.5924(17)x10^-19 Coulombs. -
Period: to
The Discovery of Subatomic Particles by Ernest Rutherford (1871 - 1937)
Performed "gold foil" experiment with Hans Geiger and Ernest Marsden in 1909: some alpha particles were deflected and reflected back on the gold foil. Proving the plum pudding model wrong because atoms had an ultra-dense center, most particles could pass through because most of atom's volume was empty space and if it hits nucleus it would be deflected, or reflected. Suggested existence of protons to be part of nucleus (1920) and neutrons to make up for missing mass of nucleus (1921). -
The Introduction of Atomic Number by Henry Moseley (1887 - 1915)
Flawed periodic table: position predicted by atomic weight didn't always match position predicted by chemical properties. Shot high-energy electrons at different chemical elements & measured wavelength & frequencies of resulting X-rays; found each element emits X-rays at a unique frequency. Got linear line graph by plotting square-root of X-ray frequency against elements’ atomic numbers; found element’s atomic number is same as # of protons & element is defined by its # of protons. -
Period: to
The Discovery of The Third Subatomic Particle, Neutron, by James Chadwick (1891 - 1974)
By 1920, physicists knew most of atom's mass was the nucleus and this central core contained protons. 1932: After repeated experiments bombarding Beryllium atoms with alpha radiation, he had evidence of a new kind of radiation, the subatomic particle, neutron. It had the same mass as a proton, but was neutrally charged. And it also added mass with protons in the nucleus to solve the question why mass-to-charge ratio for nuclei didn't match up and was approximately twice the mass expected.