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Democritus (460 B.C.E- 370 B.C.E)
(*dates are in B.C.) Democritus created the first model of the atom. He gave a picture of an atom and separated the different atoms by their shape, size, and arrangement. He also explained that atoms were attached either by hooks and eyes, or ball and sockets. He said that this was how the atoms bonded together. He was referred to as an atomist during his time and was criticized for his theories. He said that all matter is made up of atoms. (http://www.universetoday.com/60137/democritus-model/) -
John Dalton (1766-1844)
John Dalton came up with his theory due to his interest in researching gases. Through his research and various experiments he hypothesized that elements combine at the atomic level in fixed ratios. His model focuses on five thorems.
1) Elements consist of atoms.
2) Atoms of an element are all the same for that element.
3) Atoms of different elements can be told apart by their atomic weight.
4) Elements combine to form chemical compounds.
5) Atoms can't be created or destroyed
www.nndb.com -
Dimitri Mendeleev (1834-1907_
Dimitri Mendeleev arranged elements into seven different groups according to their properties. This led to the creation of the first periodic table. The first periodic table was in order of atomic weight, rather than atomic number. He also came up with the Periodic Law.
http://atomictimeline.net/ -
Marie Curie
Marie Curie and her husband Pierre Curie discovered through experimentation that radioactive material cause atoms to break down spontaneously. During this process, the atoms release radiaton through the form of energy and subatomic particles.
http://www.angelfire.com/mb2/atoms/ -
Henri Becquerel
In 1900 Becquerel isolated electrons in radiation. In 1902, he presented the discovery radioactivity. He also studied the physical properties of cobalt, nickel, and ozone, studied how crystals absorb light, and researched the polarization of light.
http://www.nndb.com/people/608/000072392/ -
JJ Thomson (1856-1940)
JJ Thomson's atomic model said that no matter where matter came from, it contained particles that were the same and are smaller than the atoms that matter is formed from. He came up with this theory using a cathode ray scope. He was also the man who discovered the electron and came up with the Plum Pudding Model. This explained the different charges of atoms. (https://sites.google.com/site/thomsonsexperiment/jj-thomson-s-atomic-model-and-theory) -
Ernest Rutherford
Through experimenting with with his gold foil experiment, Rutherford came up with the idea that an atom has a central positive nucleus that is surrouded by negative electrons that orbit the nucleus. He also said that the majority of the mass was in the nucleus and that the rest of the atom was mostly empty space.
http://www.rsc.org/chemsoc/timeline/pages/1911.html -
Henry Moseley (1887-1915)
Another scientist who studied under Ernest Rutherford, Henry Moseley developed an idea of usind X-rays to study atomic structure. This idea also helped with the placement of the elements in the periodic table, making it more accurate. This then led to the arrangement of elements using their atomic number, rather than their atomic mass.
http://www.chemistry.co.nz/henry_moseley.htm -
Neils Bohr
Neil Bohr's came up with a representation of the atom. Through the Bohr Model, one can see how many electrons can be in each electron orbit. The model can also show give an idea of how an atom may appear and how different elements are combined. It explains how many electrons each orbit can hold. Niels Bohr atomic theory was a combination of Rutherford’s model and quantom mechanics.
http://chemistry.tutorvista.com/inorganic-chemistry/niel-bohr-atomic-theory.html -
The Wave Model of the Atom
This model of an atom is an improvement to the Bohr Model. The only thing different about this one is how electrons operate. It describes the electrons as a wave, rather than a particle. It also states that electrons are found in pairs in orbitals of the atom. This idea gives the probability of locating electrons in a particular location, unlike that in the Bohr model. The wave model also forms the basis for the quantum theory. http://www.commonsensescience.org/atom_models.html -
James Chadwick
While James was working as a student under Erneset Rutherford, he proved the existence of neutrons. After this discovery, he and other scientists began experimenting with neutrons and discovered nuclear fission. http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html -
Aristotle (384 B.C.E -322 B.C.E.)
Aristotle's theory of the atom was that all matter was made of the four elements: fire, water, earth, and air. In his model, there were two forces which were conflict and harmony. The elements were said to move to their designated place where they would then be at rest. Conflict was thought to bring bad, while harmony was thought to bring good. He did not really believe in atoms, therefore he developed his own theory witht the four elements. http://www.universetoday.com/62400/aristotle-atomic-t
