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600 BCE
Democritus: Discovered the atom
Democritus broke a shell in half and broke a piece in half over and over until he couldn’t anymore and realized he’d found indivisible pieces of life. -
Antoine Lavoisier: Found mass is conserved in a chemical reaction; named oxygen in 1778 and hydrogen in 1783
He performed quantitative experiments that demonstrated to role of oxygen in combustion and metal calcination, ending phlogiston theory and Greek four element theory. He also named oxygen in 1778 and hydrogen in 1783 -
Law of Conservation of Mass
Developed by Antoine Lavoisier -
John Dalton: Proposed the first atomic theory
He experimented with gasses to discover total pressure of gaseous mixture is sum of partial pressures each gas exerts while in same space. -
Dalton's Atomic Theory
The theory states all matter is composed of atoms, indivisible and indestructible building blocks and all atoms are identical, but different elements have atoms of differing size and mass. -
Dmitri Mendeleev: Created the periodic table
Mendeleev realized physical and chemical properties were related to atomic mass of elements in a periodic manner. He also corrected known the atomic masses and predicted properties of elements he didn't even know to exist. -
J.J. Thomson: Discovered and identified the electron (the first subatomic particle discovered)
His most important experiment was putting two oppositely charged electric pates in a cathode ray tube to discover the cathode ray was composed of negatively charged particles. Thomson determined mass-to-charge ratio of cathode ray particles -
Cathode Ray Tube: Led to the identification of electron
Scientists discovered something was traveling from the anode because a shadow was cast on a glowing wall. -
Plum Pudding Atom Model
Developed by J.J. Thomson -
Gold Foil Experiment: Developed by Ernest Rutherford
It measured the angle that a particle’s scattered after going through thin metal foil. It took 5 years starting in '08 for Rutherford to complete the experiment -
Robert Millikan: Determined the electrical charge/value of a single electron
He developed the oil drop experiment that measured the charge present to droplets in oil mist. It proved the force on any charge in the field is the product of charge and electric field. Millikan measured both electric force and magnitude of electric field. -
Ernest Rutherford: Discovered the nucleus and the proton
The most important thing Rutherford did was develop the gold foil experiment. -
Rutherford Model
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Bohr Planetary Model
Created by Niels Bohr -
Niels Bohr: Determined the structure of atoms and contributed to quantum theory
Bohr established a theory about how energy is transferred in defined quantities and electrons move around the nucleus in prescribed orbits to keep them from losing energy and spiraling into the nucleus. -
Henry Moseley: Discovered atomic number of each element using x-rays which organized the periodic table better
X-ray radiation has a precise mathematical relationship with atomic numbers -
Erwin Schrödinger: Described the likelihood of finding an electron in a certain position
Used mathematical equations to take the Bohr model even further and, with Werner Heisenberg, determined regions in which electrons would most likely be found -
Quantum Mechanical Model
Created by Erwin Schrödinger -
Electron Cloud Model
Created by Erwin Schrödinger and Werner Heisenberg -
James Chadwick: Discovered the neutron and proved it was a neutral particle of the nucleus and determined its mass and speed
Using head on elastic collision, scientists saw the energy given off was greater than a nucleus could do so Chadwick determined it was a neutral particle, not a photon and tested it on nitrogen, oxygen, helium, and argon -
Sources 1
1) http://thelittleguy22.tripod.com/id1.html#:~:text=%22Atoms%22%20in%20Greek%20means%20%22,and%20break%20it%20in%20half.
2) https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/history-of-atomic-structure/a/discovery-of-the-electron-and-nucleus
3) https://www.biography.com/scientist/john-dalton#:~:targetText=Dalton's%20experiments%20on%20gases%20led,Dalton's%20Law%20of%20Partial%20Pressures. -
Sources 2
4) http://chemed.chem.purdue.edu/genchem/history/gold.html
5) https://courses.lumenlearning.com/boundless-chemistry/chapter/discoveries-leading-to-nuclear-atom-model/#:~:targetText=Cathode%20rays%20carry%20electronic%20currents,which%20he%20called%20%E2%80%9Celectrons.%E2%80%9D
6) http://chemed.chem.purdue.edu/genchem/history/lavoisier.html
7) https://www.beautifulchemistry.net/lavoisier
8) https://www.britannica.com/biography/Robert-Millikan -
Sources 3
9) https://www.britannica.com/science/Millikan-oil-drop-experiment
10) https://www.atomicheritage.org/profile/james-chadwick
11) http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/neutrondis.html#:~:targetText=Discovery%20of%20the%20Neutron,mass%20of%20this%20neutral%20particle.&targetText=This%20analysis%20follows%20that%20for,a%20much%20more%20massive%20one. -
Sources 4
12) http://www.abcte.org/files/previews/chemistry/s1_p6.html#:~:targetText=In%201926%20Erwin%20Schr%C3%B6dinger%2C%20an,mechanical%20model%20of%20the%20atom.
13) https://www.nobelprize.org/prizes/physics/1922/bohr/facts/#:~:targetText=In%201913%2C%20Niels%20Bohr%20proposed,but%20only%20in%20prescribed%20orbits.&targetText=Bohr's%20theory%20could%20explain%20why%20atoms%20emitted%20light%20in%20fixed%20wavelengths.
14) http://abyss.uoregon.edu/~js/glossary/bohr_atom.html -
Sources 5
15) https://www.msnucleus.org/membership/html/jh/physical/atomictheory/lesson1/atomic1g.html
16) https://courses.lumenlearning.com/introchem/chapter/john-dalton-and-atomic-theory/#:~:targetText=Dalton's%20atomic%20theory%20proposed%20that,of%20differing%20size%20and%20mass.
17) https://corrosion-doctors.org/Periodic/Periodic-Mendeleev.htm
18) https://www.khanacademy.org/partner-content/big-history-project/stars-and-elements/knowing-stars-elements/a/dmitri-mendeleev -
