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Period: 435 to
Atomic Theory Timeline
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442
Democritus
442 B.C. Domcritus came up with the theory of atoms; he said the universe is made up of empty space and an infinite number of invisible particles that are different because of their arrangment, form, and position. -
Antoine Lavoisier
Lavoisier made careful quantitative measurements which allowed the compositions of compounds to be determined accurately. Had the original idea that inspired the Law of Definite Proportions. -
Law of Conservation of Mass
This law was established by Antoine Lavoisier, and it states that mass is neither created nor destroyed in any kind of ordinary chemical reaction. -
Dalton's Atomic Theory
Dalton noticed that oxygen and carbon combined to make two compounds. After this he came up with the Law of Simple Muliple Proportions. His theory stated that each element is made up of atoms, the reason that elements are pure is because all the atoms are the same. He also said that the reason elements are different from one another the reason is that there are different atoms involved. -
John Dalton
Dalton proposed the Atomic Theory which
stated that all matter was composed of small indivisible
particles called atoms. He also stated that three types of atoms exsist; simple, compound, and complex. -
Dmitri Mendeleev
Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on atomic mass. He also left space for new elements, and predicted three yet-to-be-discovered elements including eke-silicon and eke-boron. -
J.J. Thomson
Thomson showed that electrons have negative electric charges and come from ordinary matter. For matter to be electrically neutral, there must also be positive charges lurking somewhere. -
Cathode Ray Tube
This device was discovered by Karl Ferdinand Braun. A cathode is a stream of electrons leaving the negative electrode, or cathode in a discharged tube or emitted by a heated filament in certain electron tubes. -
Plum Pudding Atomic Model
This model proposed that the negatively charged electrons were mixed with smeared-out positive charges. Explaining the neutrality of bulk material. -
Robert Millikan
Millikan discovered the charge of electrons by using his oil drop experiment. -
Earnest Rutherford
Rutherford's experiment showed that the vast majority of alpha particles acted as expected, and hardly moved at all, but there were alpha particles that scattered through angles greater than 90 degrees. -
Gold Foil Experiment
Ernest Rutherford and his coworkers conducted an experiment intended to find the angles through which a beam of alpha particles (helium nuclei) would scatter after passing through a thin foil of gold. -
Rutherford's Model
In Rutherford's Model the electrons orbit the nucleus. However, under this model, there is nothing to prevent the electrons from losing energy and falling into the nucleus under the influence of its Coulomb attraction. -
Henry Moseley
Developed the application of X-ray spectra to study atomic structure. His discoveries resulted in a more accurate positioning of elements in the Periodic Table by closer determination of atomic numbers. -
Niel Bohr
Bohr applied quantam theory by assuming that electrons travel in stationary orbits defined by their momentum. -
Bohr Planetary Model
The Planetary Model explained the orbit of electrons pertaining to quantum physics. This model describes electrons orbiting in fixed energy levels. This suggested electrons can only move up or down to other energy levels. -
Erwin Schrodinger
Schrodinger developed wave mechanics which describe the behavior of quantum system. -
Quantum Mechanical Model
Several scientist throughout history worked on this model throughout differet periods of time, but two of them are Erwin Schrodinger and Albert Einstein This model is based on mathematics and the quantum theory. This model of the atom uses compound shapes of electron clouds, volumes of space in which there is likely to be an electron. This model is based on possibility rather than certainty. -
Electron Cloud Model
The cloud model is an atom model where electrons are no longer depicted as particles moving around the nucleus in a fixed orbit, but we don't know exactly where they are, and hence describe their probable location around the nucleus only as an arbitrary cloud. The idea of the electron cloud model came about by multiple scientist including Ernest Rutherford, Niels Bohr, Werner Heisenberg, and others. -
James Chadwick
Chadwick made a fundamental in nuclear science, he proved the exsistence of neutrons.
