home

__1. Early Greeks : Aristotle, Democritus__ []
 * __A Timeline to Show the Development of the Model of an Atom__**.

Aristotle, the son of Nicomachus, was born in Stagira, Greece. While only eighteen years of age, Aristotle left home and traveled to Athens to become a member of Plato’s Academy. Plato and Aristotle were always in constant contact while Aristotle studied and taught until Plato’s death. For the next twelve years, Aristotle not only taught but also conducted research in biology, zoology, botany, and physiology in many different places. During those twelve years, he tutored a young boy who would later become Alexander the Great. After those twelve years, Aristotle returned home to Stagira which was rebuilt by Alexander the Great for his gratitude to Aristotle. In 335, Aristotle returned back to Athens where he started up a school for twelve years named the Lyceum, also identified as the “Peripatetic School” for the reason that people studied while walking around. After Alexander the Great died in 323, Aristotle left Athens to live in his late mother’s estate in Chalcis in Euboea until he died. Aristotle did not agree with the atom theory that emerged at about 400 BC. This theory stated that an atom is the smallest piece of matter. Aristotle’s belief, which could only be his opinion because there was no way to prove it otherwise scientifically, was that everything is constructed from the four elements: fire, water, earth, and air. Incidentally, most people liked his theory more. He believed not only that the four elements made every piece of matter but he also believed that they each had a characteristic: dryness, hotness, coldness, and moistness. Because of that belief, he held the idea that fire was dry and hot, water was cold and wet, air was hot and wet, and earth was dry and cold. To understand the grouping better, here is a chart that explains it simply.
 * Aristotle (384 – 322 BC)**

[]

Aristotle believed that the two forces in his model: conflict (which brought about bad things) and harmony (which brought about good things), caused the elements to naturally fit into their proper spots. Aristotle also thought that there was a fifth element which single-handedly consisted of the heavens named aither. However bizarre this theory may seem today, people believed in it for about two thousand years until the scientific revolution. Aristotle’s contribution to the history of the atomic theory is monumental.

http://improbable.org/era/physics/atom.html http://www.netplaces.com/philosophy/aristotle-the-master-of-those-who-know/the-life-of-aristotle.htm

http://www.gap-system.org/~history/Biographies/Democritus.html

Democritus, born in Abdera, lived to be 90 years old.When he was younger, his teacher was Leucippus. Democritus shared Aristotle's view of atomism and did not believe it. Instead, he proposed his own atomic theory. In his theory, atoms are eternal and always move. Those atoms bounced together and combined to become the assets that we have today. He, however, believed that the earth always had and always will exist.His theory also claims that no specific size will be given to atoms,and that there are various factors that part-take in influencing them. Here is a video that explains his theory simple. http://www.youtube.com/watch?v=RvuaZ6EEUgs&feature=player_embedded
 * Democritus (460-370 BC)**

In his opinion, an atomic theory included that there could be no physical parts or unoccupied space. For the atomic theory, the physical universe had two basic ingredients: impenetrable atoms and penetrable space. Another branch of the belief is that atoms cannot be destroyed and cannot be created, so there is a constant number of them in the universe. This fundamental principle of Democritus's atomic theory includes matter conservation which is the sum total in the universe doesn't increase or decrease. Even though Democritus' view of the atom has been modified multiple times, his main belief remains the fundamental framework of modern science.

http://www.gap-system.org/~history/Biographies/Democritus.html http://democritusatomictheory.com/ http://www.bookrags.com/biography/democritus/ __2. Alchemists__ [] Alchemists are people who believed in Alchemy. Alchemy is a medieval chemical science that was widely used in the Middle Ages by monks and scientists. It also speculates philosophy that aims to achieve the transmutation of the base metal into gold, a cure for disease, and the discovery of a means of prolonging life. The Alchemists created the atomic theory from Aristotle’s idea after he guessed that water, earth, fire, and air could be changed by the action of heat and cold or damp and dryness. Their views didn’t give a way to an atomic theory method until about two hundred years ago. A legend said that alchemy was founded by Hermes, the Greek god. They also believed that each metal was represented by one of the bodies of the solar system. 1) Transmutation of lead and other base metals into gold 2) Discovery of the “elixir of life” 1) Hot intense climate 2) Closed group, secretive The alchemical works need a lot more caution than a regular chemistry lab would need. Spiritual energy is the first energy used out of the alchemic energies. In order for the experiment to happen, the alchemist needs to make sure that the lab that is being performed is not hostile to the different energies used in the laboratory. The key of alchemy stays in the laboratory. It also creates a link between the alchemist and the operation. There are also two types of works in the alchemist laboratory: the delicate ones and the others. The delicate works are when the operator is alone and cannot work with other people. If the alchemist does work with someone else when they are not supposed to, their lives can be endangered. The others are when the alchemist can have people working in the laboratory with him.
 * TWO MAJOR GOALS OF ALCHEMISTS:
 * WORKING CONDITIONS

Used science and “magic” in devoting their time to change substances from one form to another.

It is a popular belief that Alchemists made contributions to the "chemical" industries of the day—ore testing and refining, metalworking, production of gunpowder, ink, dyes, paints, cosmetics, [|leather tanning], ceramics, glass manufacture, preparation of extracts, liquors, and so on (it seems that the preparation of //[|aqua vitae]//, the "water of life", was a fairly popular "experiment" among European alchemists). Alchemists contributed [|distillation] to Western Europe. The attempts of alchemists to arrange information on substances, so as to clarify and anticipate the products of their chemical reactions, resulted in early conceptions of chemical elements and the first rudimentary [|periodic tables]. They learned how to extract metals from ores, and how to compose many types of inorganic acids and bases.

[]

[]

[|http://en.wikipedia.org/wiki/Alchemy#Relation_to_the_science_of_chemistry]

[] __3. Antoine Lavoisier__

[] Laviosier and his wife Marie-Anne Pierette Paulze []

**Antoine Lavoisier** **(1743-1794)**
He was born and raised in France where he attended the Collège Mazarin and studied mathematics, science, astronomy, botany and geology. He married Marie-Anne Pierette Paulze (See picture above) who became very useful in helping him translate his experiments and data into English and many other things. He experimented with and studied sciences in Paris, France during the "Chemical Revloution." This time period resulted in what we know today as our modern chemistry. Lavioisier is often called the Father of Modern Chemistry because his discoveris fueled this era of the "Chemical Revolution". Some of his discoveries were that water is made from oxygen and hydrogen molecules and he created the first version of __The Law Of Conservation Mass__ in 1785. This law states that matter is neither created nor destroyed in a chemical reaction. See this video for a further explination of the law of conservation mass. [] Lavoisier discovered __The Law of Conservation Mass__ when he was experimenting with combustion. He thought when something combusted, it combined with some componant of the air. When he was experimenting with mercury, he found that the combined masses of mercury and oxygen were the same as the uncombined masses. When he hypothesized that this should be true with all chemical changes, he experimented more and proved that mass is not obtained or lost during a chemical reaction. In addition, a major accomplishment of Lavioisier was that he published the first "periodic table of elements". It was more of an extensive "list of elements" but even though there were substances that weren't elements in it and it was incomplete, it stimulated more research and led more scientists to become interested in the elements. []

[] [] [] [] __4. Dalton__ Datlton's Life: John Dalton was an English Chemist who lived from 1766-1844. He was the son of a Quaker handloom weaver, the youngest of three surviving children. They say he was born sometime around September 6th, 1766, in Eaglesfield, however no exact records exist. He attended school until he was 11. At age 12 he then proceeded to become a teacher. For about a year he next worked as a farmer, but at 15 he returned to teaching, privately for the most part, pursuing it as a full time job, for the remainder of his life. Dalton's lifelong interest in meteorology did much to make that study a science. He began keeping records of the local weather condition factors including: atmospheric pressure, temperature, wind, and humidity. During this time he recorded more than 200,000 values, using equipment which for the most part was made by him. Dalton's interest in the weather gave him a special interest in mixtures of gases. His earliest studies were concerned with atmospheric physics. This sparked the formulation of his law of partial pressures also known as commonly as, "Dalton's law" which was formally announced as a law in 1803. It defined the pressure of a mixture of gases as the sum of the pressures given off by each component occupying the same space. Dalton lived a simple life, keeping very strict to his Quaker faith. He never ma conrried. During most of his life he had little money and was almost overly concerned with his economic status. However, by tutoring and doing routine chemical work at low pay he was able to afford the few things he truly wanted. His voice was rather harsh, especcially when lecturing and he was thought to be rather stiff, or tense, and awkward in manner. He is said to have had no grace in conversation or in writing. Despite his lack of social skills, Dalton was a brillian man and he apparently lived a quite happy life and had many friends. In 1810 Dalton refused an invitation to join the Royal Society but was finally elected in 1822 without his knowledge. As his fame grew, he received many honors, including a doctor's degree from Oxford in 1832, at which time he was presented to King William IV. It was such a grand occasion that he had to wear the famous scarlet regalia of Oxford, which fortunately looked gray to his color-blind eyes and therefore was acceptable to him as an orthodox Quaker. In 1837 he suffered a stroke; the following year, in 1838 he suffered another leaving him with impaired speech. And lastly a final stroke came on the night of July 26, 1844, which caused his death. Theory: Dalton's theory was that elements could be told apart by the weight of their atoms. This theory suggests that: 1) All matter is composed of atoms 2) Atoms cannot be made or destroyed 3) All elemnets of the same element are identical 4) Different elements have different types of atoms 5) Chemical recations happen when atoms are rearranged 6) Compounds are formed from the constituent elements This theory was used explain unknown chemical happenings. Today, scientists use this theory as a base for help undertsanding elements' atomic weight. It is also used for things like nuclear fission or atomic fission. [] [] [|http://www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html] http://www.universetoday.com/38193/john-daltons-atomic-theory/ __5. J.J.Thomson__ http://en.wikipedia.org/wiki/J._J._Thomson http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html http://www.experiment-resources.com/cathode-ray.html
 * = [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/J.J_Thomson.jpg/200px-J.J_Thomson.jpg width="140" height="217" link="http://en.wikipedia.org/wiki/File:J.J_Thomson.jpg"]] ||

J. J. Thomson was born on December 18, 1856 and died on August 30, 1940. He was born in Cheetham Hill, a suburb of Manchester, and married Rose Elizabeth where they had two children. J. J. Thompson was a great physicist who finished second in his class at Cambridge University. J. J. Thompson is the known discoverer of the electron. He measured the charge of the particles in 1899 and because of this work, he was given the Noble Prize in 1906 and knighted in 1908.

His first experiment was to build a cathode ray tube with a metal cylinder on the end. This cylinder had two slits in it, leading to electrometers, which could measure small electric charges. He found that by applying a magnetic field across the tube. There was no activity recorded by the electrometers, so the charge had been bent away by the magnet. This proved that the negative charge and the ray were inseparable and intertwined.

His second experiment was about proving that rays had a negative charge. He thought the vacuum in the tube was not good enough, so he found ways to back it up. Thomson constructed a slightly different cathode ray tube this time, with a fluorescent coating at one end. Halfway down the tube were two electric plates. They produced a positive anode and a negative cathode. As he expected, the rays were deflected by the electric charge, proving that the particles were charged and carrying a negative charge.

His third experiment was to work out the nature of the particles. They were too small to have their mass or charge calculated directly. He attempted to lessen this by how much the particles were bent by the electrical currents. Thomson found out that the charge to mass ratio was so huge that the particles carried a massive charge or were a thousand times smaller than a hydrogen ion.

A major discovery of Thomson is that he discovered the electron. That event is so major in scientific history. It changed the way science works forever. It gave scientists a new look on atoms. Thomson also discovered the radioactivity of potassium, which is vital to humans. We have a lot of potassium in our diets, so too much of it would be bad because of the radioactivity. He also demonstrated that hydrogen had a single electron per atom. This gave scientists another new look at how the element worked. It was important when putting together the periodic table. __6. Robert Millikan__ http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html#

Robert A. Millikan was born on March 22nd, 1868 in Morrisan, Illinois. Millikan died on December 19th, 1953. He was the son of Reverend Silas Franklin Millikan and Mary Jane Andrews. Though born in the United States he attended both Universities in United States and Germany, at the Universities of Berlin and Göttingen in Germany. __Millikan's Experiment__ The Millikan Oil Drop Experiment helped Millikan determine the size of the charge of an electron. He also determined that there was a smallest "unit" charge or that charge is "quantized." He determined how to put a charge on a tiny drop of oil, and measure how strong an applied electric field had to be in order to stop the oil drop from falling. Since he could find the mass of the oil drop, he could then calculate the force of gravity on one drop and then determine the electric charge one drop must have. Millikan started his research on the charge of an electron because he wanted to become a full professor at the University of Chicago. To begin his experiment, Millikan used a small sub millimeter of oil that was held between capacitor plates in order to measure the increasing charge of the atom. This was done since he knew that the drop of oil would increase in charge because of the friction, once the oil went between the plates. Because Mullikan was continuously watching the motion of the oil drops, he then compared how long it took the drop to fall with the electrical plates off, with the time it took for the oil drop to fall when voltage was added. Millikan was then able to find that once the drop connected with the electric field, it would always occur in very discrete units. With this information, it was concluded that the electron charge was a single value, and also the same value for all different forms of electricity. Robert Millikan's Oil Drop Experiment was able to resolve the conflict by concluding the charge and mass of the electron. Because of Millikan's excellent work, Niels Bohr, a Danish physicist, was able to determine Rydeberg's constant and provide the first and key proof of the new atomic theory.

Read more: [|Robert Millikan - Chemistry Encyclopedia - number, mass] [|http://www.chemistryexplained.com/Ma-Na/Millikan-Robert.html#b#ixzz1fQkO34fg] Read more: [|Robert Millikan - Chemistry Encyclopedia - number, mass] [|http://www.chemistryexplained.com/Ma-Na/Millikan-Robert.html#b#ixzz1fQd2NQjG]



__7. Ernest Rutherford__ **Ernest Rutherford** []

Erest Rutherford was born on August 30th, 1871 in New Zealand, and died on October 19th, 1937 in Cambridge, England. He was the son of James Rutherford, a farmer, and his wife Martha Thompson. He studied at McGill University as well as University of Manchester. After college Rutherford married Mary Georgina, and had one daughter together. Rutherford established the nuclear structure of the atom and the essential nature of radioactive decay, he was known as "The Father of the Nucleus". []

Ernest Rutherford has many famous quotes, some of his famous quotes are, “If you can't explain your physics to a barmaid it is probably not very good physics," and "All science is either physics or stamp collecting,” this quote is saying that in science physics is everything. Another quote is "If your experiment needs statistics, you ought to have done a better experiment," which is saying when you do an experiment you are going to get a lot of statistics and if you don't, you didn't do the experiment right. "Of all created comforts, God is the lender; you are the borrower, not the owner," which shows that he believes in God and you can be a scientist and still believe in God. []

[]

Ernest Rutherford's atomic theory was based upon a central, positive nucleus surrounded by negative orbiting electrons. The model of this theory showed that most of the mass of an atom was from the nucleus. __http://www.rsc.org/chemsoc/timeline/pages/1911.html__

This video shows his atomic theory: __http://www.youtube.com/watch?v=cirICBV0LYk__

In 1909 the Geiger-Marsden experiment or Gold-foil experiment was conducted. At first Rutherford discovered that a flash of light was given off when a -particle hit into a screen coated with zinc sulfide. The experiment started out as Rutherford and Geiger sitting in the dark until their eyes became sensitive enough. Rutherford discovered that when the light hit the ZnS the beam of -particles were broadened. He then had Geiger measure the angles at which the light was given off. The conclusion was consistent, set to 1 degree per angle. Geiger and Rutherford then suggested that Marsden conduct an experiment, seeing if any -particles will scatter at a wider angle. The results were a 1 in 20,000% at larger than 90 degrees. Rutherford concluded that the positive charge and the mass of an atom were a slight fraction of the total volume. He also concluded that the scattering -particles through a given angle is in proportion to the thickness of the foil. The experiment was published in 1911 with a model of an atom (below). His final conclusion was that all of the positive charge and the majority mass is contributed by the nucleus __http://chemed.chem.purdue.edu/genchem/history/rutherford.html__
 * __http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/rutherford-model.html__


 * __http://www.wix.com/fightingps/gregbandyrocks/rutherfords-experiment/rutherfords-experiment/rutherfords-experiment__

__http://www.youtube.com/watch?v=PgtYJzHNHLI&feature=related__

** __8.Niels Bohr__ **
[]

Niels Bohr, born in Copenhage, Denmark on October 8th, 1885, as an important person in the world of science who made a great discovery which now affects our world and knowledge of science today. He was the son of Christian Bohr, a Professor of Physiology. Bohr attended the Copenhagen University, he received his master's degree in Physics in 1909 and his Doctor's degree in 1911. Bohr started his scientific research under the guidance of Professor C. Christiansen. His focus was directed to research of the atomic nuclei. His model of the atom lead him to be the winner of the Noble Prize in Physics in the year 1922. Niels Bohr died at the age of 77 on November 18th, 1962. Bohr started by doing experiments with shooting charged particles at gold foil, and realized that the particles mostly went right through the foil. This experiment led to him figuring out that an atom is, in fact, mostly empty space. Also, since the particles were positively charged, an atom must also be, since the gold foil reflected the particles.Later, he realized that atoms had to be in orbits, just like the image of an atom below.

Borh's model has 4 principles. 1. Electrons spin around a stable, stationary orbits. 2. Each orbit has energy linked to it. 3. Light is released when the electrons move from to a higher or to a lower orbit and then is absorbed. 4. The energy and frequency of light emitted or absorbed is given by the difference between the two orbit energies. Here is a video of students depicting the Bohr Model of atoms: http://www.youtube.com/watch?v=PLpZfJ4rGts&feature=related

[] http://www.epa.gov/radiation/understand/rutherford.html

__9. Heisenberg__

Werner Heisenberg (1901-1976) came up with the Uncertainty Principle. He received the Nobel Prize in 1933.

Werner Heisenberg was born on December 5, 1901 in Würzburg. He studied at the University of Munich to study physics. He became a physicist and came up with the Uncertainty Principle. It basically states that one cannot find both the momentum and position of a sub-atomic particle at the same time. It must be done separately. He was only 23 years old when he made this discovery. Besides the many awards, honors and prizes, his most treasured award is the Nobel Prize given to him in 1933. He died on February 1, 1976. The uncertainty principle is also called the principle of indeterminacy.Heisenbergs theory basically says that when two properties are being measured at the same time, no matter how accurate the measurement instrument is, quantum limits the accuracy.

Schrodinger and those who followed him favored “wave mechanics”, while Heisenberg preferred “matrix mechanics.

The uncertainty principle has to do with four properties: Momentum, time, energy, and position. The two properties being measured are not just any two, but properties that have a certain relationship. Relationships like, for example, energy and time.Properties that have this kind of relationship are called canonically conjugate. For an example, the measures are taken of a moving electron’s momentum and position. The more accurate momentum is, the less accurate position is, and vice versa. Absolute precision in one would mean completely incorrect for the other.

__10. Schrodinger et al__



Erwin Schrodinger was a extraordinary Austrian physicist (as well as a theoretical biologist) who lived from 1887 - 1961. He was the recipient of the 1933 Nobel Prize of Physics for his famed "Schrodinger's Equation".

Schrodinger’s theory, also commonly known as the quantum theory, is a procedure proposed by Erwin Schrodinger that is usually used to find energy levels and other properties of a molecule or atom. The procedure provides an equation that defines a “wavefunction”, which is multiplied by each term in the equation.



The foremost expression of the particle-wave concept and wavelengths was proposed a French physicist Louis Vector de Broglie. A Danish physicist by the name of Niels Bohr first attempted to utilize the new wave theory in his work, finding energy transitions in hydrogen atoms. Schrodinger's model of the equation is commonly referred to as the wave-mechanical model, and is, in the realm of physics and quantum science, a very general equation, allowing it versatility.

He proved this theory in an experiment called Schrodinger's Cat. In this experiment a cat is put into a steel box with a small amount of radioactive gas along with hydrocyanic acid inside of the box. If the radioactive gas decays, then it would release the hydrocyanic acid, killing the cat. But if the radioactive gas does not decay, then the hydrocyanic acid would not be released, and the cat would not die. []

Here is a link to a video that further explains the Schrodinger's Cat experiment: []

References: [|Picture of Schrodinger] [|Picture of Schrodinger's Equation] [|Picture of Schrodinger's Cat] [] http://www.nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg.html [|http://www.pha.jhu.edu/~rt19/hydro/node3.html] [|http://user.mc.net/~buckeroo/BHSE.html] http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec14.html http://c2.com/cgi/wiki?HeisenbergUncertaintyPrinciple

__11. Chadwick__

http://www.sciencephoto.com/media/223958/enlarge Sir James Chadwick discovered the neutron existed in 1932.