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John Dalton
• Elements consisted of tiny particles called atoms
• A pure element has all atoms in that element equal and have the same mass
• There are dfferent elements because different atoms of each element were different and had different masses
• Compounds are atoms of different elements combined together
• Compounds have constant composition because they contain a fixed ratio of atoms
• Chemical reactions involve the rearrangement of combinations of those atoms -
J.J. Thompson
• The atom is made up of small particles
• He discovered electrons
• Proved that atoms were made up of protons, neutrons, and electrons
• Proved that the atom is divisible
• Electrons have a charge of -1, protons have a charge of +1, nuetrons have a charge of 0
• Positively charged particles are surrounded by the negatively charged electrons
• Electrons were placed there due to electrostatic forces. -
Albert Einstein
• The presence of electrons that are produced when a beam of light is directed onto the surface of metal
• Release of atoms caused by the photoelectric effect was theorized to form an electric current
• Changed the idea that light traveled only in waves
• Brownian theory covered the irregular movement of tiny particles within a liquid or gas
• First real evidence of the presence of atoms -
Robert Millikan
• Compared the time that it took a drop of oil to fall under the influence of gravity
• Time it took for the oil to climb under the influence of applied voltage
• Used a suspended drop of oil between capacitor plates to measure the incremental charge of an electron
• Determined accurately (within one part in one thousand) the charge and mass of the electron -
Ernest Rutherford
• Most of the part of an atom is empty.
• Approximately all the mass of the atom is concentrated at the center of atom which is called the nucleus.
• In the center of the atom, the positively charged particles are present.
• The charge on the nucleus of an atom is positive and is equal to Z.e where Z is charge number, e is charge of proton.
• The negatively charged electrons revolve around the nucleus in different circular orbits.
• Central region (nucleus) is -
Niels Bohr
• Electrons would have only certain chemical motions.
• Electrons in atoms orbit the nucleus in orbits that have a set size and energy.
• The lowest energy is found in the smallest orbit, since the energy of the orbit is related to its size.
• When electrons moves or jumps from one orbit to another one, electrons emitted the radiation with a frequency $\nu$ determined by the energy difference of the energy levels according to Planck relations -
Erwin Schrodinger
• A quantum mechanical model can predict the odds of the location of the electron
• a nucleus is surrounded by an electron cloud
• Where the cloud is most dense, the probability of finding the electron is greatest
• the electron is less likely to be in a less dense area of the cloud.
• this model introduced the concept of sub-energy levels -
URLs (Info and Pictures)
DaltonDalton: http://timerime.com/en/event/479466/Dalton/
Thompston: http://www.tutorvista.com/science/jj-thomson-atomic-theory-0 http://www.2011modelsb.wikispaces.com
Millikan: http://www.chemistryexplained.com/Ma-Na/Millikan-Robert.html
Rutherford: http://physics.tutorvista.com/modern-physics/rutherford-s-gold-foil-experiment.html
http://chemistry.tutorcircle.com/inorganic-chemistry/rutherford-model-of-the-atom.html -
URLs (Info and Pictures)
Einstein:http://www.ehow.com/info_10040964_einsteins-atomic-theory.html
Bohr: http://chemistry.tutorvista.com/inorganic-chemistry/niel-bohr-atomic-theory.html http://jurusanipa.blogspot.com
Schrodinger:http://abcte.org/files/previews/chemistry/s1_p6.html
DISCLAIMER: ALL OF THE RESEARCH I DID ONLY GAVE ME THE YEAR OF EXPERIMENTS, SO I SET ALL OF THE DATES TO JANUARY 1 OF THAT YEAR
