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427 BCE
Plato
Plato is the pre-eminent Greek philosopher who was convinced that atoms of matter must derive from these fundamental solids: triangles, squares, pentagons, and hexagons. worldhistory.org/plato/ -
400 BCE
Democritus
He developed the "seed" theory into the concept of the atomic universe. Democritus introduced the idea of the atom as the basic building block matter worldhistory.org/Democritus/ -
850
The Alchemists
The Alchemists discovered several new substances, which today we recognize as elements, but at the time were characterized as strange blends of the principles of fire, earth, water and air, and mercury, sulfur and salt. uwaterloo.ca/chem13-news-magazine/february-2019/feature/ancients-and-alchemists -
Robert Boyle
Boyle defined elements in Sceptical Chymist as "certain primitive and simple, or perfectly unmingled bodies; which not being made of any other bodies into which they are ultimately resolved." He believed that chemical experiments could demonstrate the truth of the corpuscularian philosophy. sciencehistory.org/historical-profile/robert-boyle -
Antoine Lavoisier
He named the elements carbon, hydrogen and oxygen; discovered oxygen's role in combustion and respiration; established that water is a compound of hydrogen and oxygen. famousscientists.org/antoine-lavoisier/ -
John Dalton
He formulated the Law of Partial Pressures according to which the pressure of a mixed gas is the sum of the pressures that each of its components would exert if occupying the same place. Dalton's theory was based on the concept that each element consists of its own unique brand of invisible atom. scienceandindustrymuseum.org.uk/objects-and-stories/john-dalton-atoms-eyesight-and-auroras#atomic-theory -
Billiard Ball Model
The billiard ball model came by because John Dalton thought atoms were the smallest particles of matter, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model the atoms. flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/3.12/primary/lesson/daltons-atomic-theory-ms-ps/ -
Amedeo Avogadro
Avogadro published multiple papers discussing the masses of atoms, their compounds, their gas densities, the proportions in which they combine, and the physics of matter. He is regarded as one of the founders of atomic-molecular chemistry. https://www.famousscientists.org/amedeo-avogadro/ -
Dmitri Mendeleev
Mendeleev found that when all the known chemical elements are arranged in order of increasing atomic weight, the resulting table displayed a recuring pattern of properties within groups of elements. britannica.com/biography/Dmitri-Mendeleev -
Plum Pudding Model
The plum pudding model has electrons surrounded by a volume of positive charge, like negatively charged "plums" embedded in a positively charged "pudding". J.J. Thomson contributed massively to the model of the atom and the modern day theory. breakingatom.com/glossary-of-terms/plum-pudding-model -
Pierre and Marie Curie
Pierre and Marie discovered the strongly radioactive elements polonium and radium. Marie coined the term radioactivity for the spontaneous emission of ionizing, penetrating rays by certain atoms. britannica.com/science/atom/Discovery-of-radioactivity -
Albert Einstein
Einstein realized that the random chaos of jostling, invisible molecules would produce statistical fluctuations-for example, once in a while a small group of invisible molecules could, just for a moment, move in mostly the same direction. ans.org/news/article-969/albert-einstein-and-the-most-elemental-atomic-theory/ -
JJ Thomson
Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. khanacademy.org/science/chemistry/electronic-structure-of-atoms/history-of-atomic-structure/a/discovery-of-the-electron-and-nucleus -
Ernest Rutherford
Found that the atom is mostly empty space, with nearly all of its mass concentrated in a tiny central nucleus. britannica.com/biography/Ernest-Rutherford -
Robert Millikan
Robert Millikan succeeded in precisely determining the magnitude of the electron's charge. nobleprize.org/prices/physics/1923/milikan/facts -
Niels Bohr
He proposed a theory for the hydrogen atom, based on quantum theory that some physical quantities only take discrete values. nobleprize.org/prizes/physics/1922/bohr/facts -
Solar System Model
The "solar system" model describes an atom as a central massive positive entity (the nucleus/sun) and, orbiting around it, the negative entities (the electrons/planets). socratic.org/questions/what-is-the-problem-with-a-solar-system-model-of-the-atom -
Henry G. J. Moseley
Mosely published a paper in 1914 in which he concluded that the atomic number is the number of positive charges in the atomic nucleus, He also firmly established the relationship between atomic number and the charge of the atomic nucleus. britannica.com/biography/Henry-Moseley -
Electron Cloud Model
The electron cloud model is a model of an atom, in which the atom consists of small but massive nucleus surrounded by a cloud of rapidly moving electrons. The model defines the zone of probability describing the electron's location, because of the uncertainty principle. nuclear-power.com/nuclear-power/reactor-physics/atomic-nuclear-physics/fundamental-particles/what-is-the-electron-properties-of-electron/electron- cloud/ -
James Chadwick
James Chadwick discovered the neutron in 1932 and was a member of the British MAUD Committee. atomicheritage.org/profile/james-chadwick -
Werner Heisenberg
Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle’s position and momentum cannot both be known exactly. For that discovery he was awarded the Nobel Prize for Physics. https://www.britannica.com/biography/Werner-Heisenberg -
Erwin Shrodinger
He proposed the quantum mechanical model of the atom, which treats electrons as matter waves. britannica.com/biography/Erwin-Schrodinger