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442 BCE
Democritus (Ancient Greek)
- The first to introduce an atomic model. Key points include:
- Invisible particles called atoms and a void (empty space) which exists where there are not atoms.
- Atoms are indestructible and unchangeable.
- Atoms differ in shape, size, mass, position, and arrangement.
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400
Alchemists
400 A.D. - 1400 A.D.- Transmuted common elements into gold. Significance of doing this is because they believed there were seven base elements signifying the seven known heavenly bodies. Famous alchemists include Paracelsus (father of pharmacology) and Agricola (worked with sulfuric and nitric acids).
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John Dalton
- Discovered Dalton's Atomic Theory:
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms. De Leon, N. (n.d.). Dalton's Atomic Theory. Retrieved from http://www.iun.edu John Dalton [Online image]. (n.d.). Retrieved November 4, 2019 from http://www.quakersintheworld.org -
J.J. Thomson
- Through experiments with cathode ray tubes, Thomson proved that all atoms contain negatively charged subatomic particles known as electrons. Thomson produced a Plum Pudding Model (which turned out to be incorrect) that models electrons flowing in a positively charged pudding/soup.
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Ernest Rutherford
- Rutherford bombarded alpha particles in a thin sheet of gold. Some particles were veered from their initial trajectory suggesting a positive particle being present in the gold foil. Resultingly, the Rutherford's Model of Atoms was proposed, modelling the presence of a proton.
https://www.toppr.com Ernest Rutherford [Online image]. (November 3, 2019). Retrieved November 4, 2019 from https://en.wikipedia.org -
Max Planck
- Created the quantum theory of energy which illustrates that energy is radiated in 'very minute and discrete quantized amounts' opposed to the traditional notion of it being released in a continuous and unbroken wave.
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Harriet Brooks
- Worked to elucidate the nature of radioactivity in hopes of making the effects of radiation clear. Brooks's research included work with thorium in which she discovered the atomic recoil (recoil of a radioactive atom's nucleus).
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Hantaro Nagaoka
- Nagaoka developed the first published quasi-planetary model of the atom.
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Einstein
- Einstein discovered the photoelectric effect which is when protons, or 'packets of light', are shone on metal and result in the ejection of electrons from the surface of that metal. Planck's quantum theory of energy helped Einstein prove the photoelectric effect.
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Robert Andrews Millikan
1908 - 1917 Was able to measure the charge of an electron quantitatively using the Millikan's oil-drop apparatus. Chemed.chem.purdue.edu authors (n.d.). Robert Millikan. Retrieved from http://chemed.chem.purdue.edu/genchem/history/millikan.html -
Niels Bohr
- Bohr proposed the notion that energy is transferred in 'certain well defined quantities'. The defined quantities are also known as orbits which have different energies. This sorting method of electron's energy explains why atoms emit light in fixed wavelengths.
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Maurice de Broglie
- De Broglie suggested that all matter has wave properties. This became known as the de Broglie hypothesis which proposed wave-particle duality, an essential part of quantum mechanics.
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Satyendra Nath Bose
- Bose Discovered quantum statistics which allowed for a new way to derive Planck's radiation law.
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Werner Heisenberg
- Heisenberg is the creator of quantum mechanics. Contributing to an increased understanding of how all the world's physical systems work. Essentially how the world works.
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Wolfgang Pauli
- Created the Pauli principle which suggests that no two electrons in an atom can have the same set of quantum numbers. He did this by introducing a new quantum number, the spin (+/- 0.5).
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Erwin Schrödinger
- Schrödinger developed the Electron Cloud Model which depicts a dense nucleus being surrounded by a cloud of electrons at various levels in orbitals. The clouds of electrons were referred to as lobes.
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James Chadwick
- Chadwick discovered the neutron via bombarding beryllium atoms with alpha particles. By doing this, Chadwick observed that an unknown type of radiation was produced. Particles in this radiation had a neutral charge and a mass similar to a proton, this new particle became known as the neutron.
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Hertha Sponer
- Sponer contributed to the application of modern quantum mechanics to atomic and molecular by studying dissociation and excitation potential and of the spectra and structure of polyatomic molecules and their relation to chemical problems.
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Gerhard Herzberg
1936 - 1979 Determined the electronic and geometric structure of molecules. Much of his work focused on atoms that contain odd numbers of electrons (radicals). His findings were the foundation of molecular spectroscopy.- 1936 (atomic spectra and structure)
- 1939-1979 (molecular spectra and molecular structure)
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Lise Meitner
- Meitner discovered Nuclear fission for large atoms (eg. Uranium 235 or 238).
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Chien-Shiung Wu
- Worked on Nuclear fission of U-235 and U-238 via gaseous diffusion.
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Maria Goeppert Mayer
- Mayer worked with isotope abundances to determine the origin of elements and contribute to the evidence of a shell model of the nucleus.
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Bertram Neville Brockhouse
- Invented the field of neutron scattering. Brockhouse also created a device that used a neutron beam to probe solid material at the atomic level. This increased the understanding of what was holding sold materials together.
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Rudolph A. Marcus
1956 -1965 Developed a theory for electron transfer for molecules in a solution. Electron transfer is a principle prevalent in many chemical processes such as corrosion and photosynthesis. The Nobel Prize in Chemistry 1992 (n.d.) Rudolph A. Marcus Facts. Retrieved from https://www.nobelprize.org/prizes/chemistry/1992/marcus/facts/ -
Alan Guth
- Guth worked on elementary particle theory and is relation to the early universe.
