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400 BCE
Democritus
- Greek philosopher who supported the idea that at some point, matter could no longer be divided into smaller pieces
- Called the smallest particles of matter "atomos"
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Period: 400 BCE to
Alchemy
- Pseudoscience that was popular from 400 BC to 1600 AD
- Some alchemists weren't real scientists at all and they just tried to find ways to turn common metals into gold
- Many alchemists were real scientists who discovered a few elements
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Period: to
Antoine Lavoiser
- Proposed the Law of Conservation of Mass, which states that mass cannot be created or destroyed
- Explained the nature of combustion
- Published "Elementary Treatise on Chemistry" in 1798, the first modern chemistry textbook
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Period: to
John Dalton
1803 - Came up with the Atomic Theory of Matter:
1. Every element is made up of atoms.
2. Atoms of the same element are the same, and atoms of different elements are different.
3. Chemical compounds occur when atoms of different elements combine. Compounds always have the same relative numbers and types of atoms.
4. Chemical reactions occur when atoms are reorganized in the way they are bonded. The atoms themselves are not changed. -
Solid Sphere Model
John Dalton proposed the solid sphere model of the atom in 1803 -
Period: to
J. J. Thomson
- Used a cathode-ray tube to make atoms give up negatively-charged particles, which he called electrons
- Refined Dalton's theory by saying that atoms were made up of subatomic particles
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Period: to
Robert Millikan
- Measured the charge of an electron using an oil-drop apparatus and found bag the mass of an electron is at least 1000X smaller than the lightest atom
- Worked on things concerning the hot-spark spectroscopy of the elements which led to significant discoveries of cosmic radiation
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Period: to
Henry Moseley
- Created the worlds first atomic battery in 1912, which he called a radium battery
- Proved that very element's identity depends on the number of protons it has in 1913
- Correctly predicted the existence of four elements which are now called promethium, technetium, hafnium, and rhenium
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Period: to
James Chadwick
- Rutherford's assistant director of research
- Proved the existence of neutrons in 1932 which led to advances in the atomic bomb
- The first atomic bomb detonated in 1945 with help from Chadwick
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Plum Pudding Model
- Model of the atom proposed by Thomson
- Consisted of a cloud of positive charges embedded randomly with negative electrons
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Ernest Rutherford
- Tested Thomson's model and concluded that it was not entirely correct
- Made a model that showed the positive protons contained within a small nucleus in the atom and the electrons rotating around the atom
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Neils Bohr
- Created a model of an atom that shows electrons moving around the nucleus in orbits
- Proposed that the number of electrons in the outer orbit of an atom affected the properties of the atom and that electrons could jump between orbits and emit or absorb a photons as they did so
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Louis de Broglie
- Suggested that matter in motion, specifically electrons, has properties associated with the properties of waves
- His idea was based on a proposal made by Einstein 20 years earlier
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Wolfgang Pauli
- Introduced two new numbers and formulated the Pauli Exclusion principle which stated that no two electrons in an atom could have identical sets of quantum numbers
- Solved the non-relativistic theory of spin
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Erwin Schrodinger
- Came up with the Schrodinger equation which describes the motion of energies of particles. This led to the quantum-mechanical model of atoms which describes electron behavior in terms of wave mechanics
- Created the electron cloud model of the atom based on his idea of how electrons moved
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Internet Sources
http://www.famousscientists.org/james-chadwick/
http://www.physicsoftheuniverse.com/scientists_pauli.html
http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html
http://chemed.chem.purdue.edu/genchem/history/millikan.html
https://www.britannica.com/biography/Louis-de-Broglie
http://www.atomicarchive.com/Bios/Bohr.shtml
http://abyss.uoregon.edu/~js/glossary/bohr_atom.html -
Book Sources
Chemistry Sixth Edition, Zumdahl
The World Encyclopedia of Science, Volume II, Physics Today, World Books, Inc.
Student Handbook Volume 2, The Southwest Company
