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370
ARISTOTLE
Sometime in 370 B.C Aristotle believed in 5 elements; air which was light, earth which was cool and heavy, water which was wet, fire which was hot, and Aether which he said was a divine substance that planets and stars were made up of. he believed that all matter was made up of one of those elements, or a combination of them. This view had a negative influence because it hindered the exploration of the atomic model. Aristotle did not conduct any expieriments to validate his theory. -
460
DEMOCRITUS
In 460 BC, Greek Philospoher Democritus came up with a theory for the atomic model. HIs theory stated that no particle could be broken down forever, eventually there would only be one particle left, and that particle would be indivisible. His model was an invisible sphere that contained no nucleus and no electrons, it only had solid matter on the inside. this was the first atomic model. Democritus did not do any expieriments for his theory, it was based off of flimsy evidence. -
JOHN DALTON
English chemist, John Dalton, created the Atomic Theory of Matter. He used Democritus’' teachings and findings to help his research; Dalton believed in the idea of an atom and said all atoms could not be created nor destroyed. Dalton's theory of spherical, solid atoms was based on measurable properties of mass. Dalton's theory stated that matter is composed of atoms of differing weights that combine into ratios. -
LAW OF DEFINITE PROPORTIANS
French chemist Joseph Proust stated that "I shall conclude by deducing from these experiments the principle I have established at the commencement of this memoir, viz. that iron like many other metals is subject to the law of nature which presides at every true combination, that is to say, that it unites with two constant proportions of oxygen. In this respect it does not differ from tin, mercury, and lead, and, in a word, almost every known combustible." therefore, all elements are proportional -
Henri Becquerel
Becquerel studied different properties of the atom, including radioactivity. In 1903, he was awarded many Nobel Prizes for Physics for his studies of radioactivity. His discovery continually helps scientists to create the ideal atomic model. -
J.J. Thomson- Cathode Ray Tube Experiment/ Plum Pudding Model
The electron was discovered by performing the cathode ray tube experiment, which had changed the model of the atom at that time. When the electron was discovered, the atom was still said to be a solid ball, and Thomson redefined that theory. He was awarded the Nobel Prize for Physics in 1906 for his discovery of electrons. Thomson then created the plum pudding atomic model. Which was a circle with positive energy and electrons roaming about inside. -
THE QUANTUM THEORY
Max Planck created the Quantum Theory. He realized that wave form energy can only be allowed in specific quantities, which helped with the finding of energy levels in atoms. This discovery added to the growth of the atomic model. -
ROBERT MILLIKAN
Robert Millikan, an American physicist who studied the properties of electrons, discovered the overall charge of electron by conducting an experiment called the "falling drop method." He concluded that the charge of electrons was constant throughout every trial. Because of this experiment, Millikan was the inspiration for other scientists to further explore the atomic structure. -
GOLD FOIL EXPIERIMENT
Ernest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved throwing of radioactive particles through thin metal foils (gold) and detecting them using -
GOLD FOIL EXPIERIMENT (PART2)
This experiment involved throwing of radioactive particles through thin metal foils (gold) and detecting them using screens coated with zinc sulfide. Rutherford found that although the majority of particles passed straight through the foil approximately 1 in 8000 did not. That experiment led him to create his idea of atoms having empty space. -
NIELS BOHR
Niels Bohr received a Nobel Prize for his contributions to the atomic structure and quantum mechanics. Bohr had helped solve the problems with the nuclear model of the atom and he said that electrons moved in fixed orbits around the nucleus. -
UNCERTAINTY PRINCIPLE
Heisenburg stated that it was impossible to measure the velocity and the precision of an electron at the same time -
QUANTAM MECHANICAL MODEL
Austrian scientist Erwin Schrodinger disagreed with Bohr's theory. Because of this, he created his own theories, which lead to the discovery of the Quantum Mechanical Model. This model had a nucleus along with an electron cloud to hold the electrons. -
JAMES CHADWICK
Discovered the neutron when pondering why the number of protons differed from the Atomic Number.
