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History of the Atomic Model

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Elena Moran

on 25 September 2014

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Transcript of History of the Atomic Model

History of the Atomic Model
First proposed the idea that an ultimate particle exists
Said that all matter including time and space are made up of tiny indestructible particles
(460-370 BC)
-Disagreed with the atomic theory proposed by Democritus.
-He theorized that all substances were made out of small amounts of the four elements: Earth, Water, Air, and Fire.
Aristotle's Theory:
Because his works were so well respected, the general public chose to accept Aristotle's theory and reject the more accurate one proposed by Democritus.
He also said that the atoms cling together in many different combinations to make other objects
Ernest Rutherford
By 1911, the world knew that the atom was comprised of subatomic particles, however, no one really knew how these particles were arranged or how they functioned.
J.J. Thomson (who was Rutherford’s contemporary) had a theory that the atom was a spherical cloud of positive charge with electrons sprinkled evenly throughout:

It was called the plum pudding model
Rutherford decided to test Thomson’s theory with an experiment of his own.
The deflected Alpha particles in Rutherford's experiment proved that inside the atom, there must be a dense nucleus of other particles blocking the Alphas' path.
Niels Bohr
Niels Bohr was Ernest Rutherford’s protege. Essentially, Bohr took Rutherford’s more simple (but still very accurate) model of the atom, and made two discoveries:
1. Electrons orbit around the positively charged nucleus in individual paths.
2. The number of electrons in the outermost orbit can be used to determine the properties of the element.
The current model of the atom is "Bohr's model"
In 1803, he calculated the atomic weights of elements and put them in a table.
There were only 6 elements at the time and they were hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus.
He got the calculations from percentage compositions of compounds by “using an arbitrary system to determine the probable atomic structure of each compound.”

John Dalton
His atomic theory still has principles that are unchanged to this day.
Elements are made out of the smallest particles and they are atoms.
All atoms of an element are identical.
Atoms of different elements can be differentiated by their atomic weight.
Atoms of different elements can be mixed into for a chemical reaction to make chemical compounds.
Atoms cannot be created, destroyed, or divided because of being the smallest particles of matter.
Henry Moseley
In 1913, he observed and measured the x-ray spectra different chemical elements. He noticed a relation between wavelength and atomic number. This discovery is now called Moseley’s law
Before this discovery, atomic numbers were based on sequence of atomic weights and were just an arbitrary number.
Now this organized the periodic table in order with atomic numbers for the elements. He predicted missing elements and their periodic numbers for the Periodic Table. This discovery helped sort out what confused scientists for a long time.
James Chadwick
In 1932, he “bombarded beryllium atoms with alpha particles.” Then came an unknown radiation. After he interpreted what the radiation and what the mass was for a proton, he came to the conclusion that it was a neutral electrical charge and called it a neutron. An adequate model of the atom was available for chemists now with the neutron.
Rutherford shot extremely small alpha particles into a sheet of gold atoms. If J.J. Thomson’s model were correct, then theoretically the alpha particles should've shot right through the positively charged proton cloud. As Rutherford began to collect data, he noticed that for the most part the particles passed through the gold in accordance to Thomson’s model, however, some of the particles
shoot straight through the gold, but
off at odd angles.
Luis Walter Alvarez
Was on the research team for making the atomic bomb in 1940
Studied atoms and discovered subatomic particles in an atom using hydrogen bubble chambers
Marie Curie
Previous discoveries of Henri Becquerel inspired Marie Curie’s research. She studied uranium and thorium, and called their spontaneous decay process "radioactivity." Along with her husband, she also discovered the radioactive elements polonium and thorium.
Robert Millikan
Robert Millikan is credited for determining the exact charge and mass of an electron, and proving that this quantity was constant for all electrons. He did this using the “falling drop method.”
The method consisted of dropping small globules of oil over a magnet into the path of an x-ray. When the x-ray particles made contact with the oil, the charge would change causing the oil to fall slower, stay still, or even start rising.
J. J. Thomson
Thomson investigated a long-standing puzzle known as "cathode rays." He proposed that these mysterious rays were streams of particles much smaller than atoms, and were actually minuscule pieces of atoms. He called these particles "corpuscles," and suggested that they might make up all of the matter in atoms.
After several experiments, he found that the rays were made up of electrons, and that these electrons were indeed negatively charged particles that were fundamental parts of every atom.
384-322 BC
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