stephen.gasecki.timothy.graham.atomichistory.fall.2009


 * __ATOMIC TIMELINE__ **

**Ancient Times (450 AD and years prior)**

__Democritus __ ( 460 BC to 370 BC ) Country- Abrader, Greece Discovery- "atomos " or Atoms 410 BCDemocritus was an, believed indivisible particles known as atoms, which are infinite in number and various in size and shape, and perfectly solid, no internal gaps. also believed in the hi my name is barney ;) Void, or the nothing. Atoms move about in this void where they repel and collide with one another forming clusters which in turn form visible objects. Depending on the arrangement of this atoms would decide what it is we perceive. Macroscopic objects in the world that we experience are really clusters of these atoms, and growth or relative change is caused by aggregation or scattering of atoms.



Democritus' small, spherical, solid, indivisible model.

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__ Aristotle __ ( 384 BC to 322 BC ) Country- Stageira, Greece Discovery- Four Elements 350 BC

Aristotle was a Greek philosopher, and considered to be one of the three most influential Western minds.His father was a doctor, which most likely means he was trained in investigation of natural occurrences. He grew up as an orphan from the age of ten, living with his uncle. At eighteen years old, Aristotle left his home to become a student of Plato. The period of time from when he was eighteen, until he turned 37, is to believed to be when he conducted most of his works. One of the greatest ironies however, was that if it a scientific finding was not in Aristotle it was not accepted causing a great set back.

Aristotle challenged Democritus' atom theory, instead he believed there was no smallest part of matter, but rather all substances were made up of the four elements. Neither Democritus or Aristotle could prove their theory by a valid experimentation. Aristotle's views prevailed in the end mostly because more people believed in his reasoning.

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__ Plato __ ( 429 BC - 347 BC ) Country- Greece Discovery- Small Particles 360 BC

Plato was Aristotle, and many other great philosophers' teacher in ancient Greece. He is believe to be taught by Socrates another one of the great minds of the period. Plato's philosophy, in both his age and the current, has it influences on political and intellectual movement of the time. It can be said that from some of Plato's writing, the current saying beauty is in the eye of the beholder may have originated since some of his philosophies focused on goodness, and beauty.

Plato is not credited directly with the idea of small particles, but he is said to be the one to instill this thought within Aristotle. He believed that there has to be something smaller than what we can perceive. He also, knew that things could not just appear out of nowhere, and something happens to create what it is we experience as an object.

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 * 1700-1800 **

__ Antoine Laurent Lavoisier __ ( 26 August 1743 – 8 May 1794 ) Country- France Discovery- Early Law of Conservation of Mass

Antoine Lavoisier was born the son of a prospective lawyer, and thought to follow in his footsteps. Rather then becoming a lawyer for his life, Antoine chose to become a geologist. He was an active believer in the need for reform in France, and played a great role in the French Revolution. He gained interest in Chemistry at a time when it was not exactly considered to be a science. During this time was the idea of the Phlogiston Theory for combustion. This Theory he would interpret and ultimately come out with the beginning for the idea of Law of Conservation of Mass.

Lavoisier, rather then follow the crowd, decided that the idea for something to sometimes have positive, negative, and sometimes no weight as presented by the Phlogiston Theory. After studying combustion he concluded that the reaction included air. He would disprove the Phlogiston Theory and also present the Law of Conservation of mass.

[[|http://cti.itc.virginia.edu/~meg3c/classes/tcc313/200Rprojs/lavoisier2/home.html]]

__John Dalton__ ( 6 September 1766 - 27 July 1844 ) Country- England Discovery- Atomic Theory John Dalton is arguably the most important person in Chemistry. Born in England in 1766 he grew up a Quaker. He studied several different sciences and taught at his home town. On his own time he would study atoms and other basic chemistry. He was the first to develop the modern atomic theory. His theory consists of five main points.

1.) Elements are made up of tiny, indivisible particles called "atoms" 2.) All atoms in a give element are identical. 3.) All atoms and elements are defined by their atomic weight. 4.) Atoms can combine with other atoms to form chemical compounds. 5.) Atoms cannot be created or divided into anything less than one.

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__Charles Coulomb__ ( 1736 - 1806 ) Country- France Discovery- Coulomb's Law -1780 Charles Coulomb is known for developing Coulomb's law: "the definition of the electrostatic force of attraction and repulsion." His name is equivalent to the SI unit of charge, the coulomb,. He discovered the law that states "The force between two electrical charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them". It is the main force involved in atomic reactions.

A Torsion Balance as used by Coulomb is defined as " device used to measure the gravitational acceleration at the Earth’s surface. Other such devices, using different methods to obtain the same result, are pendulums and gravimeters. The __torsion balance__ consists essentially of two small masses at different elevations that are supported at opposite ends of a beam. The latter is suspended from a wire that undergoes torsion because the masses are affected differently by the __force of gravity__ . When __the wire__ is twisted, an [|optical system] indicates the angular deflection (//θ//), and the torque (T), or twisting force, involved can be calculated from the simple expression T = //kθ,// in which //k// is a constant that depends on the properties of the instrument."

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**1800-1875**

__William Crookes__ ( 1832 - 1919 ) Country- England Discovery- Crookes Tube 1870 William Crookes is most famous for the discovery of his Crookes tube. Born in England in 1832, he began work mid-life. He was first credited with the discovery of a pure sample of Helium. His discoveries and inventions added to a long line of chemists and furthered the study of science particularly in England. He died in 1919, after a long life of researching the atom.

Crookes did his research by developing the "Crookes tube", an experiment involving a vacuum for his study of electricity in low pressure gases. He took a glass tube and created a vacuum inside of it. He then put a large positive electrical charge on one side and turned off the lights. He found that small particles were attracted to the metal on the side furthest from the charge and the negative electrode (cathode) appeared to emit rays. The Crookes tube lead to many other atomic discoveries later on in time.

A Crookes Tube [[]]

__Wilhelm C Roentgen__ ( 1845 - 1940 ) Country- Germany Discovery- X-ray 1874 Roentgen was born in Lennep, Prussia. He utilized Crookes tubes in his experiments. He was expelled for refusing to reveal the identity of a classmate guilty of drawing an unflattering portrait of one of the school's teachers. Not only was he expelled, he could not subsequently be admitted into any other Dutch or German gym.

He carefully constructed a black cardboard covering for the Crookes Tube. Roentgen darkened the room to test the opacity of his cardboard cover, and when he charged the Crookes tube the barium platinocyanide screen he had set up to test he idea began to shimmer a few meters away. He then realized a new type of ray must be responsible for this phenomenon.

X-ray of His Wife's Hand

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__Amedeo Avogadro__ ( 1766 - 1856 ) Country- Italy Discovery- Avogadro's Principle His father was a distinguished lawyer and civil servant, and in 1799 was made president of the senate. He became a practicing lawyer by the age of twenty. Avogadro began to practice mathematics and science in his private time with his brother. In 1809 became professor of natural philosophy at the college of Vercelli. He was married and had six children.

Avogadro's Principle is that equal volumes of all gases at the same temperature and pressure contain the same number of molecules. This was used to show that Dalton's thought of multiple atoms were called molecules. Avogadro did not come up with the number, but instead the ratio of atoms in a molecule which is also known now as moles.

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**1875-1900**

__Joesph J Thomson__ ( 18 December 1856 - 30 August 1940 ) Country- England Discovery- Electron 1898 J.J. Thompson's discovery of the electron complicated the chemistry scene, and proved that atoms could be further divided. He is credited with the discovery of both the electron and isotopes. Born in Manchester, his Scottish father died when he was only sixteen. Thompson was an extremely good teacher, were as himself, seven of his research students, and his son all won Nobel Prizes.

Thompson used a cathode ray tube during his experimentation. In his experiments he tested the properties of the ray and observed it reactions to the variables he introduced. After three different experiments he was able to conclude that electrons exist and he used his plum pudding model to explain it. In the electrons of the atom scattered about in a positively charged pudding. The idea being that one of the electrons could be easily singled out which is no longer considered true.



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__Henri Becquerel__ ( 1852 - 1908 ) Country- France Discovery- Radioactivity 1896 Henri Becquerel was born into a family of scientist. He was a civil engineer for a career, and became chief engineer in the Department of Bridges and Highways. The SI unit for radioactivity (Bq) is name in his favor.

Henri discovered radioactivity while investigating naturally occurring phosphorescence. In preparation for an experiment he wrapped the fluorescent material in photographic paper, and black covering, but before the experiment took place in the sunlight he found the photographic paper already exposed with a picture of the material. He concluded radioactivity from this mistake.

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__Marie Curie__ ( 1867 - 1934 ) Country- France Discovery- Polonium and Radium 1898 Marie Curie was the daughter of a high school teacher. She learned some science from her father. She went on to become a Professor and a Director of the Curie Laboratory in the Radium Institute of the University of Paris. Most of her research was conducted with her husband, who was also a scientist, by her side.

Marie and her husband took a material called Pitchblend, which contains the radioactive element Uranium, and slowly went through the tons to isolate the radioactive components. This took several years for them to accomplish. What they found was more than one radioactive element in the material they had left, one of which was far more radioactive than Uranium.

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**1900-1915**

__Robert Millikan__ ( 1868 - 1953 ) Country- USA Discovery- Charge of an Electron 1908 Millikan was an American physicist, and won the Nobel Prize in Physics. He went to high school in Iowa, and earned his doctorate from Columbia University. He was the first to graduate with a PhD from that department. He introduced conceptual questions into the introductory textbooks which he co-wrote. He had three sons, and died of heart attack in California.

Millikan used his Oil Drop Experiment to measure the charge on an electron. He placed a negative and positive charge in the machine itself, and squirted a fine spray of oil which would fall through a small hole one atom at a time. He then exposed the atoms to a ray which would induce some type of charge on the atoms. After observing this many times he realized a constant value; the charge on an electron.

Oil Drop Experiment Video [[]]

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__ Neils Bohr __ ( 1885 - 1962 ) Country- Denmark Discovery- The Bohr Atom 1913 Neils Bohr was born in Copenhagen, Denmark. His father was a professor of physiology and the university there. He originally studied physiology at the university, but after he won a competition, he abandoned it for physics. After schooling, Bohr studied under both J.J. Thompson and Ernest Rutherford. Bohr's original model of an atom was based off of one of Rutherford's theories. Bohr also worked on The Manhattan Project.

Bohr introduced the theory of electron's traveling in orbits around the nucleus and the chemical properties of the atoms depending on how many are in which orbit, while he was studying under Rutherford. Bohr also would theorize that when an electron would drop from one outer orbit to a lower, the atom would emit a photon, or light. Bohr used he physics to prove some of these theories.

Planetary model - The Planetary model was Bohr's idea. He knew that most the mass of an atom was centralized so he placed the nucleus there. Bohr also had studied angular momentum and knew that the electrons followed paths around the nulcues, this helped him to design the planetary like explain for an atom. Bohr and Rutherford would continue to build on this idea and later came up with a better model.

Rutherford-Bohr model - This model is a combination of both Bohr's Planetary model, and Rutherford's thought. They would further Bohr's original thought and expand on it but both putting it into three dimensions, and that most of the space surrounding the atom was empty. This model is designed after our solar system.

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__Ernest Rutherford__ ( 1871 - 1937 ) Country- England Discovery- Nuclear theory of an atom 1909 Ernest Rutherford is Known as the father of nuclear physics. He discovered the positive charge in the nucleus of an atom, which is now referred to as the proton. Rutherford was born the son of a farmer in England, and soon later moved to New Zealand. He attended college in New Zealand, and Cambridge. He worked to advance the chemistry field most of his life, and contributed with the planetary model of an atom.

Ernest Rutherford set out to prove the plum pudding model of an atom. He designed his gold-foil experiment so that alpha-particles would pass through a thin foil with minimal deflection, and show up on the detector on the other side. However, when he did so a few of the particles were reflected back towards him after hitting the central nucleus. This is the beginning of the nuclear theory of an atom.

Rutherford's Gold Foil Experiment

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**1915-1950**

__Erwin Schrodinger__ ( 1877 - 1961 ) Country- Austria Discovery- Electron as a Wave 1926 Erwin Schrodinger was the first to think about explaining the movement of an electron in an atom as a wave. In 1926 he published his work, which was the basis for the atomic model that Niels Bohr proposed based on his findings. The equation at the heart of his publication became known as Schrödinger's wave equation. This was the second theoretical explanation of electrons in an atom, following Werner Heisenberg's ideas. Many scientists preferred Schrödinger's theory since it could be visualized, while Heisenberg's was strictly mathematical. this caused a split in physicists ideas, but Schrödinger soon proved the two theories were identical, only expressed differently.

Schrodinger's Electron cloud model - In the electron cloud model electrons, rather than following fixed orbits, are bound to an atom and observed more frequently in certain areas around the nucleus which are called orbitals. The electron cloud allows electrons to transition between orbital states. Each orbital has a characteristic shape and energy. Whenever an electron changes orbitals the atoms gives off energy or gains depending on which direction the electron moves.

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__Werner Heisenberg__ ( 1901 - 1976 ) Country- Germany Discovery- Uncertainty 1939 Werner was a German physicist that was responsible for coming up with quantum theory and the uncertainty principle. Heisenberg was one of the principal scientists leading research and development in the German nuclear energy project during WWII. He believed that an atom bomb could not be built before 1945, and would require significant monetary and manpower resources. Post war he was appointed director of the Kaiser Wilhelm Institute for Physics.

Werner's Experimentation consisted of extremely in depth calcutions and equations. He worked closely with Bohr. Together they made several predictions and calculations using different devices. One device Heisenberg used during his matrix expirements was an anharmonic oscillator. An anharmonic oscillator is an ocillator that does not follow a simple harmonic motion.

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__ James Chadwick __ ( 1891 - 1974 ) Country- England Discovery- Neutrons 1932 James Chadwick is the discoverer of the previously unknown particle the neutron. James was Born in Chesire, England, and in WWI, he was interned in a P.O.W. camp just outside of Berlin. He spent most of his time after the war working in Germany. James' discovery of the neutron allowed for a new way to disintergate an atom, thus leading to the atomic bombs creation not to long after.

In 1930 it was discovered that Beryllium, when bombarded by alpha particles, emitted a very energetic stream of radiation. This stream was originally thought to be gamma radiation. However, further investigations into the properties of the radiation revealed contradictory results. Like gamma rays, these rays were extremely penetrating and since they were not deflected upon passing through a magnetic field, neutral. In 1932, Chadwick purposed these rays were the missing particle in the atom and actually Rutherford's neutron. Chadwick used physics to proved his theory.

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