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The Atomic Model
Transcript of The Atomic Model
Over time, the structure of an atom, the basic unit of all matter, has changed. Many scientists and philosophers have analyzed how this unit is structured, therefore, creating the modern atomic model.
Aristotle 384-332 B.C.E
Aristotle believed that all matter was created from the four elements: water, fire, air, and earth.
His idea was widely accepted, especially by the catholic church.
Democritus' idea was ignored for several years because of the elemental idea.
Democritus 460-370 B.C.E
Democritus, a Greek thinker, began the inquiry of what matter was made up of.
He stated that matter could be divided up until a certain point.
He thought all matter was made up of small individual particles, called atoms, which could not be divided.
Alchemists 100 B.C.E - 1400 C.E
Alchemists attempted to convert common metals into gold.
They failed, but in the process, studied several chemical properties of elements.
They broke down the composition of the four "elements", discovering several elements.
Alchemists discovered phosphorous in their experiments with urine.
Antoine Lavoisier- 1772-1794
He understood and emphasized what is now known as the law of conservation of matter.
Made the first Periodic Table of elements, containing about 33 elements, some of which were not real elements.
John Dalton 1803
Dalton performed several experiments revolving around the properties of gases and discovered that air was a mixture.
By using the laws of conservation of mass, definite proportions, and multiple proportions, Dalton proved that elements were made from atoms.
Introduced the first atomic masses
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"Chemsoc Timeline." Chemsoc Timeline. The Royal Society of Chemistry, 2001. Web. 26 Oct. 2013.
"Development of the Atomic Theory." Development of the Atomic Theory. N.p., 2007. Web. 26 Oct. 2013.
Hakim, Joy "The Story of the Arom" American Federation of Teachers, 2002. Print
LeMay, H. Eugene. Prentice Hall Chemistry: Connections to Our Changing World. Needham, MA: Prentice Hall, 2002. Print.
Villanueva, John C. "Electron Cloud Model." Universe Today RSS. N.p., 25 Aug. 2009. Web. 26 Oct. 2013.
Walker, Jim. "History of Atoms." History of Atoms. N.p., Sept. 1988. Web. 25 Oct. 2013.
John Dalton's Atomic Theory:
All matter is composed of matter
Atoms cannot be made or destroyed
Atoms can combine with other elements to make compounds
In chemical reactions, atoms can be separated and rearanged
Atoms of the same element are identical, having the same size, mass, physical and chemical properties
Different elements have different atoms
Sir William Crooks 1879
With an experiment regarding cathode rays, Crookes discovered that the rays were not light and had a charge. He saw that they traveled in straight lines, his experiment aided JJ Thompson's.
While experimenting with an electron beam in a gas tube, he discovered a new type of radiation, x-rays. The rays passed through his wife's skin, but they demonstrated the outline of his wife's bones and ring.
W. K. Roentgen 1895
JJ Thomson 1897
The electron was discovered by JJ Thompson. By passing an electric current through gas in a cathode ray tube, and an electric field around the tube, creating positive and negative sides, the electron was discovered.
Said negative charges were within the atom
The atom was divisible, there were particles smaller than the atom
There were positively charges particles in the atom
Plum Pudding model, positives and negatives, with the electron able to be removed
Max Planck 1900
Created the quantum theory of energy. By adding energy to atoms, vibrating particles of light could emit only certain forms of energy. The energy was determined in color or frequency, not intensity. When atoms are vibrated at a certain frequency, the energy can be measured. The energy packets were called quanta.
Albert Einstein 1905
Wrote that light absorption can release electrons from atoms in the "photoelectric effect". He created the equation, E=mc^2 which translates to, an increase of energy (E) will cause the mass (m) to increase, by the speed of light (c), squared. Einstein calls his energy packets photons. He believed that there had to be a minimum threshold energy, or energy level where chemical absorption happens.
Ernest Rutherford 1911
With an experiment using gold foil and alpha particles, Ernest Rutherford created his own Atomic theory. Rutherford shot alpha particles at a sample of gold foil, he found that most particles went straight through, however, few bounced back.
Rutherford's Satellite Model
The atom is mostly empty space
The nucleus of an atom is tiny compared to the whole atom
All of an atom's positively charged particles are found in the nucleus
The negatively charged particles, electrons, are scattered, like satellites, around the nucleus.
Neils Bohr 1913
He based his model on Rutherford's atomic model. He put the electrons in specific energy levels.
He based his model on the "spectral lines" of hydrogen
By heating hydrogen, he saw how the electron moved because of the increase and decrease of energy.
Bohr's Atomic Model
This model is called the planetary model.
Electrons orbit around the nucleus like a planet around the sun
The orbitals are located at specific distances from the nucleus
Erwin Schrodinger 1930
Schrodinger took Bohr's model of the atom and found, through mathematical equations, where it was likely to find an electron.
Predicts the odds of the location of where an electron can be found.
It also demonstrates where the electron has been.
His model is called the electron cloud model
James Chadwick 1932
James Chadwick discovered the neutron. He used scattering data in order to find the mass of an atom.
Rutherford first noticed that the protons and electrons could not account for the entire mass of the atom.
By bombarding a Beryllium atom, with radioactive rays, he noticed that the atom emitted neutral particles that had an almost identical mass to protons.
Electron cloud model
Where the cloud is most dense, there is a higher probability of finding an electron
Where it is less dense, there is little chance of finding an electron
Represents the probable areas to find an electron