-
200
Democritus Atom
(Date really 400 b.c.)
The scientist Democritus was responsible for this model of the atom. It was the first model of the atom ever to have been thought of and was accepted in 400 B.C. He didn't conduct a specific experiment to develop this model, he just thought that there must be some sort of building block that makes everything up. He was, of course, right. He thought that the atom was a tiny ball that could not be physically divided. The model was kind of like a tiny marble.
wikipedia.com -
200
Aristotle model
(Date really 300 b.c.)
The scientist Aristotle developed this idea of basic building blocks. He actually disagreed with the very idea of atoms and thought that everything was made of 5 elements- air, fire, water, earth, and aether (the heavens) . This idea was adopted in 300 B.C. He thought that there was nothing that couldn't be divided into further subdivisions, including the idea of atoms. He was, in a way right, we now know that even more smaller particles make up atoms.
wikipedia.com -
Period: 200 to
The Atom
-
Antoine Lavoisier
Lavoisier, who is considered the father of modern chemistry, defined an element as a substance that can't be chemically analyzed. He did lots of experiments with combustion and came up in about 1785 with what is now called the law of conservation of mass, which states that mass can be neither created or destroyed in a chemical reaction. This contributed to atomic theory because it bettered the understanding of chemical reactions and helped science progress.
chemed.chem.wisc.edu chemteam.info -
Henri Becquerel
In 1896, the scientist Henri Becquerel discoverd radioactivity while he was experimenting with Uranium salts. He put the salt near a photographic plate covered with opaque paper, and the paper fogged up. Later he showed that the rays emitted from uranium caused gases to ionize and could be deflected by electro or magnetic fields. This proved that atoms could be naturally radioactive, thus changing our view of atoms. He shared a Nobel Prize with Marie and Pierre Curie.
nobelprize.org -
Marie and Pierre Curie
These two scientists discovered in 1898 that the ability of atoms to radiate did not depend on the arrangement of the atoms; that it actually depended on the interior of the atom. They also found that only uranium and thorium gave off this radiation. This of course changed the whole idea of atoms and radiation. They were inspired by Henri Becquerel and shared a Nobel Prize with him in 1903.
nobelprize.org -
John Dalton Atom
Dalton thought that all elements were composed of tiny particles called atoms. He thought that all elements were made up of atoms with the same mass that were identical, and this was why they were pure. He thought that the reason elements were different was because each one had a different mass for their atom. He didn't conduct any specific experiments for these ideas, his theory was the result of a lot of work. His idea of how the atom looked was similar to Democritus'.
wikipedia.org -
Max Planck
Planck developed a theory in which energy is always emitted or absorbed in discrete units which he named quanta. This discovery revolutionized physics because it went against conventional ideas about the nature of radiation and energy. His law states that the energy of each quantum is equal to the frequency of the radiation times the universal constant - Plancks constant - which is 6.63 * 10E-34 Js.
www.thebigview.com wikipedia.org -
J.J. Thompson Atom
As well as suggesting the "Plum Pudding" model of the Atom, J.J. Thompson also discovered the electron by experimenting with what people thought were cathode rays insided glass tubes and discovering that they were instead electrons. His theory about the atomic model was that there was a positively charged sphere filled with negatively charged particles. He started the idea that atoms might be made of even smaller particles.
wikipedia.org -
Robert Millikan Electron
Millikan determined the charge of the electron by using the falling drop method in which he meaured the force on tiny droplets of oil suspended against gravity between two metal electrodes. Than he repeated this experiment for many droplets and he proved that the charge on all electrons is the same. This of course added a lot to the knowledge about the electron.
cstl-csm.semo.edu nobelprize.org -
Ernest Rutherford Atom
Ernest Rutherford conducted his famous gold foil experiment in order to get his theory of the atom. This consisted of firing radioactive particles through thin gold foil. About 1 in 8000 of the particles bounced back. His theory was that the atom had a central positive nucleus surrounded by negative orbiting electrons.
www.rsc.org -
Niels Bohr Atom
Based on Rutherfords model, Niels Bohr's model was made in 1913 by him introducing concepts from the Quantum Theory and Rutherfords dicovery of the atomic nucleus. He thought that electrons orbited around the nucleus, like how the planets orbit around the sun. He improved on the idea of atoms by saying that atoms orbit certain distances from the nucleus and do not spiral into the nucleus.
nobelprize.org http://nobeliefs.com/atom.htm -
Henry Mosely
Mosely developed the application of X-ray spectra in 1913 to better study atomic structure. This led to more accurate determination of atomic numbers, which led to more accurate postitioning of elemnets on the periodic table. This was a huge contribution to chemistry, it made information collected on all atoms and elements much more accurate nad pretty much helped with everything involving atomic theory and structure.
chemistry.co.nz -
Erwin Schrodinger
Schrodinger proposed the idea that electrons behave in a wave like manner. According to him they orbit around the nucleus in different shells and subshells. This is how he contributed to the idea of the atom. He was the one that proposed the idea that each electron shell is made up of a number of subshells.
www.green-planet-solar-energy.com chemed.chem.purdue.edu -
Werner Heisenberg
Heisenberg did not believe in picture constructs of the atom. Instead he believed in using values for hypothetical particles that could be mathematically used to calculate the probability of different energy sates and transitions among those states. He also created the uncertainty principle, which states that the position and momentum of an electron is impossible to calculate at any given point in time.
pbs.org -
James Chadwick Atom
James Chadwick dicovered the existence of the neutron in 1932 by studying an experiment in which samples of berrylium were bombarded with alpha particles. He simply put pieces of the puzzle together and realized the existence of neutrons. This was an improvement on Rutherford's Theory.
http://isaacmmcphee.suite101.com
