Daniel.Reid.Timeline.Fall.2011

Daniel Reid and Tim Patch
 * __ History of the Atom __**

** >450 AD **

Empedocles: 490-430 BC Birthplace: Agrigentum

Empedocles was a Greek Philosopher who had the idea that all material in the world was made from four different elements: Earth, Fire, Water, and Air. He also added that these elements are change based on two powers which he called Love and Strife. Love was how material would attract to one another, and Strife was how material would separate.

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[|Picture Source #1]

Democritus: 460-370 BC

Birthplace: Thrace

Democritus was really the first one to grasp onto the concept that all things are made up of really small particles. Teamed up with Leucippus, he proposed his theory of the atom, but it is unclear about the year in which he did. He thought that material was made of “atoms” so small the human eye couldn’t see them. For each material, the atoms were in the basic form of a sphere, but had different edges. Example, iron had sharp edges on its sphere which allowed it to bond with other iron atoms and form a solid structure. While although Democritus was wrong about the structure and makeup of atoms, he had found the very basic principal on the size of an atom. Really really really freakin small. [] [|Picture #2 source]

** Democritus’ model for atomic structure **

Aristotle: 384- 322 BC

Birthplace: Chalcidice

Aristotle was a student of Plato. Despite Plato’s dislike for Democritus, Aristotle was majorly influenced by Democritus. He theorized that truth could only come from observations of the universe, which was the basis for the scientific method. He also used Empedocles’ four element theories (all material is made of Earth, Water, Air, and Fire) as a basis for his four properties: hot, cold, dry, and wet. This belief was accepted until the 18th century.

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[|Picture #3 Source]

** 1700-1800 **  Joseph Priestley: March 13th 1733 – Feb. 6th 1804

Birthplace: Yorkshire, England

Joseph Priestley was a British scientist who was responsible for discovering oxygen (though it was not called oxygen) as well as being the first to create soda. He also made the first eraser, imagine that. He and Carl Scheele are both credited with the discovery of oxygen, which at the time Priestly called “dephlogisticated air.” His work //Directions for Impregnating Water with Fixed Air//in 1772, and as you expect, explained how to make soda water. []

[|Picture #4 source] Carl Scheele: Dec. 9th 1742 – May 21st 1786

Birthplace: Stralsund, Swedish Pomerania

Scheele was a chemist who has been said to have numerous chemical discoveries before the person who has been given credit for the discovery. I already stated that he was given partial credit for the discovery of oxygen, but he and Priestly did not call it oxygen when they discovered it. It has also been debated whether or not Scheele discovered elements such as chlorine, barium, hydrogen, molybdenum, along with compounds such as glycerol, lactic and citric acid, hydrogen sulfide, and many more. In 1774, Scheele tried to find a component in a mixture that he received. This mixture mainly contained manganese dioxide, and he used hydrochloric acid to treat the mixture attempting to isolate the missing component. A gas formed, and he noticed this gas would not dissolve in water. He called it “dephlogisticated muriatic acid” (At the time, hydrochloric acid was called oxymuriatic acid, they thought there was oxygen in it). []

[|Picture #5 source]

Antoine Lavoisier: August 26th 1743 – May 8th 1794

Birthplace: Paris, France

Antoine Lavoisier was deemed with the finding of the Law of Conservation of Mass, as well as proving that the two elements in water are hydrogen and oxygen. In 1772, he discovered that the products of burned sulfur and phosphorus weighed more than their original states. So if mass cannot be created or destroyed, where was the extra weight coming from? Now we know that it was the oxygen in the air combining with the reactants, but Lavoisier thought that the air had combined with the sulfur to form a gas similar to Priestley’s “ dephlogisticated air.” He called this gas oxygen. [] ** 1800-1875 **  Humphry Davy: Dec. 17th 1778 – May 19th 1829

Birthplace: Penzance, England

Davy is marked with partial credit for the discovery of chlorine. He also, through the means of electrolysis, discovered sodium, potassium, boron, magnesium, barium, and other alkali metals. In 1810, he proved that chlorine was its own element because oxygen was not present in oxymuriatic acid (yet another name for hydrochloric acid). Using this evidence, he disproved Antoine Lavoisier’s theory of acids, which explained that all acids were compounds of oxygen, when in fact all acids are compounds of hydrogen. []

[|Picture #7 source]

John Dalton: September 6th 1766 – July 27th 1844

Birthplace: Cumberland, England

After almost 2,000 years of little to no research of atomic theory, in comes John Dalton. Considered the father of modern atomic theory, Dalton looked at elements and thought, since different elements make up different material, what makes up an element? He got the idea that elements had to be made of some sort of small particle. In 1803, he came up with four postulates on atoms.

1. Each element is composed of atoms

2. Atoms in a given element are the same; atoms in different elements are different

3. Atoms cannot be divided, created, or destroyed

4. When atoms of different elements combine, they form compounds [|Picture #8 Source] Dalton determined that elements differ from one another because elements have different amounts of elements in them. He knew that the elements had to bond together, but he had no idea how. So he created a table of symbols for different elements. Not knowing at all how they could bond together, he made every symbol a circle with every element having its own decoration and atomic weight.

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** Dalton's element symbols **

Dmitri Mendeleev: Feb. 8th 1834 – Feb. 2nd 1907

Birthplace: Verkhnie Aremzyani, Russia

Mendeleev was a Russian chemist who made the first version of the periodic table of elements. In 1863, there were 56 elements known and a new one was being discovered every year. Mendeleev managed to predict how much each known element weighed as well as developed a system for predicting weights for elements that had yet to be discovered. He classified the elements into eight groups that we still use today. He managed to figure out the correct weight for hydrogen, carbon, nitrogen, oxygen, fluorine, phosphorus, sulfur, chlorine, and a few others. For any that he wasn’t 100% correct, he was really close. For him to predict the atomic weight of an individual element in in 1860’s is crazy, the fact that he was right about a lot of them is insane. On March 6th, 1869, Mendeleev presented his evidence to the Russian Chemical Society, where it was accepted. [] [|Picture #9 source]



[|Source] **Dmitri Mendeleev's Periodic Table** ** 1875-1900 **

Wilhelm Rontgen: March 27th 1845 – Feb. 10th 1923

Birthplace: Lennep, Germany

Rontgen is known for taking the world’s first ever x-ray. In November of 1895, Rontgen made a cathode ray tube, and shielded this tube with black paper. From the open end of the tube, an invisible light would pass through the paper covering the tube. He found through a series of experiments that this light could go through human skin, flesh, and tissue. He then put a piece of film a few feet away from the ray, put his wife’s hand in front of the ray, then turned it on. An image of the bones of Rontgen’s wife’s hand was on the film. Rontgen had taken the first X-ray. [] [|Picture #10 source]



J.J. Thompson: Dec. 18th 1856 – Aug. 30 1940

Birthplace: Cheetham Hill, Manchester

J.J. Thompson is credited with the discovery of the electron. In June 1897, Thompson constructed a crook’s tube, filled the tube with a gas, and out two small metal sheets on the inside. These metal sheets were meant to deflect the ray by means of using electricity. One sheet was connected to the negative side of a battery, and the other was connected to the positive side. When the ray same through, it deflected to more toward the positively charged sheet. When the two sheets were reversed on the battery, the ray deflected back to the positive side. This proved that there are negatively charged atoms in elements, thus discovering the electron. [] [|Picture #11 source]

** J.J. Thompson's Model **

Marie Curie/Henri Becquerel: (Curie: Nov. 7th 1867 - July 4th 1934) (Becquerel Dec. 15th 1852 – Aug 25th 1908)

Birthplace: Warsaw, Poland(Curie), Paris, France(Becquerel)

Marie Curie is known for her extensive research and experimenting with radiation. Becquerel is known for discovering radioactivity. Becquerel discovered radiation by observing the activity of uranium salts, which he inherited from his father. Together Marie Curie, her husband Pierre Curie, and Becquerel teamed up to research some dangerous materials. By using an electrometer (device for measuring electrical charge), Marie discovered that a sample of uranium makes the air around it conduct electricity. By doing this, she showed that radiation was not the result of interactions between molecules, but that the radiation comes from the atom itself. She submitted her findings to the Science Academy on April 12th, 1898. Pierre, Marie, and Becquerel were all awarded the Nobel Prize in Physics in 1903. Eight years later, Marie was awarded another Nobel Prize, but this time it was for Chemistry. She is one of two people that have ever received two Nobel Prizes in more than one field. [|Curie picture] [|Becquerel Picture] ** 1900-1915 **

Robert Millikan: March 22nd 1868 – Dec. 19th 1953

Birthplace: Morrison, Illinois

As J.J. Thompson was the one to discover the electron present in among atoms in an element, Millikan was responsible for figuring out the charge of an electron. He did this by using his famous oil-drop experiment. He had oil at the top of a cylinder, and allowed it to funnel through a hole so small only tiny droplets could go through. When the oil dropped, it fell in between a positively charged and negatively charged metal sheet. In addition, he also had a series of rays that caused charged when the drops fell into its path. When Millikan turn the electricity on, some drops would go to the bottom, top, or stay afloat in the middle of the cylinder. Millikan found that all the charge values were all multiples of one number, which was the charge of one electron: 1.6 x10-19 coulombs. []

Niels Bohr: Oct. 7th 1885 – Nov. 18th 1962

Birthplace: Copenhagen, Denmark

Niels Bohr was a Danish physicist who was born on October 7th 1885, and died on November 18th, 1962. Born the son of a professor, he came from a wealthy Jewish family. Becoming a prominent physicist, he became a target when Germany invaded and occupied Denmark. In 1913 he developed the Bohr model, which explained the structure of an atom, and the paths electrons take. He fled Denmark in 1943 because news that he was going to be arrested arose. The Danish resistance got him on a plane to Britain, and eventually he was recruited to work on the Manhattan Project as the "knowledgeable consultant". He died in 1962 of heart failure. http://en.wikipedia.org/wiki/Niels_Bohr [|Bohr Picture source]

**Bohr Model [|Source]**

Ernest Rutherford: Aug. 30th 1871 – Oct. 19th 1937

Birthplace: Brightwater, New Zealand

Ernest Rutherford was born in New Zealand on August 30th, 1871 and died October 19th, 1937. His gold foil experiment was key in understanding the structure of atoms. His studies produced the concept of the radioactive half- life, and theorized that atoms keep their protons and neutrons concentrated in a small nucleus, surrounded by a field of spinning electrons. He split the first atom in 1917. He was eventually knighted, and died because of a delay in receiving an operation on an umbilical hernia. http://en.wikipedia.org/wiki/Ernest_Rutherford [|Rutherford picture] **Planetary Model [|Source]** **Rutherford-Bohr Model [|Source]** ** 1915-1950 **

James Chadwick: Oct. 20th 1891 – July 4th 1974

Birthplace: Cheshire, England

James Chadwick was born October 20th, 1891, and died July 24th, 1974. He discovered the neutron in 1932. His discovery was essential to the splitting of the substance Uranium 235. He discovered that neutrons don't need to overcome the coulomb barrier and can split nuclei for elements that are much heavier. His discovery proved that the creation of elements heavier than Uranium was possible and for this he was awarded the Nobel Prize in 1935. He was then asked to participate in the Manhattan Project, which eventually created the nuclear bomb.

@http://en.wikipedia.org/wiki/James_Chadwick [|Chadwick Picture Source]

Erwin Schrodinger: Aug. 12th 1887 – Jan. 4th 1961 Birthplace: Vienna, Austria

Erwin Rudolf Josef Alexander Schrodinger was born August 12th, 1887 and died January 4th, 1961. Born in Austria the son of a botanist, he is famed for his equation, and being the one of the founding fathers of quantum mechanics. He suffered from tuberculosis, and it was actually at a sanatorium where he  discovered his wave equation. Eventually he decided he couldn't live in a country where Jews were persecuted. He went to work at Oxford University after being offered a job by Alexander Frederick Lindemann. An unusual fact about him was that he had two wives. He died at age 73 of tuberculosis.

http://en.wikipedia.org/wiki/Erwin_Schrödinger [|Schrodinger Picture source]

Werner Heisenburg: Dec. 5th 1901 – Feb. 1st 1976 Birthplace: Wurzburg, Germany

Werner Heisenburg was a German physicist who was born on December 5th, 1901, and died February 1st, 1976. He was a founding father of Quantum mechanics and is famous for his "Uncertainty Principle." It states that the position and momentum of a particle cannot be determined at any given time, which was the basis for the electron cloud model. He was loyal to his home country, and was a leader in the German nuclear energy project. He was eventually detained by England in 1945 during Operation Alsos. He died of cancer in the kidneys and the gall bladder in his home in 1976.

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**Electron Cloud Model [|Source]** ** 1950-present **

Willard Libby: Dec. 17th 1908 – Sep. 8th 1980 Birthplace: Grand Valley. Colorado

Willard Libby was responsible for discovering radiocarbon dating in 1949, which allows someone to figure out how old organic material is. This was essential for determining the age of ancient materials such as fossils and early human bones. He went on to become a professor at University of Chicago in 1945, then a professor at University of California in 1959. He was awarded the Nobel Prize in 1960 for his radiocarbon dating discovery.

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Linus Pauling: Feb. 28th 1901 - Aug. 19th 1994 Birthplace: Portland, Oregon

Linus Pauling was born in Oregon on February 28th, 1901 and died August 19th, 1994. He had already qualified for an education at Oregon Agricultural College before he had finished his high school education. He was denied his diploma though after his principal refused to let him take two classes in the spring that would finish his credit requirements. The diploma was awarded 45 years later, AFTER he won the noble prize…twice. He discovered the nature of the chemical bond and published many papers also on the speron cluster model. [] [|Pauling Picture Source]

Robert S. Mulliken: June 7th 1896 - Oct. 31st 1986 Birthplace: Newburyport, Massachusetts

Robert S. Mulliken was born in America on June 7th, 1896, and died on October 31st, 1986. He was famous as an physicist and a chemist, and was a crucial part of the making of the molecular orbital theory. He received the Nobel Prize in 1966 for his work in chemistry. He attended MIT, and after made poison gas for WWI. He then attended the University of Chicago. His work based off work of Linus Pauling made for a much easier way of calculating electronic structure. He died of of congestive heart failure on Halloween in 1986. [] [|Mulliken Picture Source]