Atomic+Theory+Sandbox

Democritus https://simple.wikipedia.org/wiki/Democritus Dalton https://simple.wikipedia.org/wiki/John_Dalton Thomson https://simple.wikipedia.org/wiki/J._J._Thomson Rutherford http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/atomstrucrev6.shtml http://kids.britannica.com/comptons/art-124956/Physicist-Ernest-Rutherford-established-the-nuclear-theory-of-the-atom http://dev.physicslab.org/document.aspx?doctype=3&filename=atomicnuclear_atomicmodelsspectra.xml

https://www.fairmontstate.edu/fsuwiki/history-chemistry In 1935, a few months after announcing his theory, Yukawa published his paper “On the Interaction of Elementary Particles.” His paper contained a series of equations that predicted the existence of a new basic particle of subatomic matter, which became known as the meson. This work brought Yukawa to the attention of physicists internationally. Scientists studying the atom at that time were puzzled by how the nucleus holds together. At Osaka University, Yukawa pondered the same question: Why doesn't the nucleus of an atom split apart? The nucleus was known to contain closely packed, positively charged protons. Since positive electric charges should repel each other, why did the protons stay together? Yukawa theorized that protons and neutrons in the nucleus attract one another by exchanging mesons. After Yukawa predicted the existence of mesons in 1935, British physicist Cecil Frank Powell and his colleagues observed charged pi mesons in 1947, confirming Yukawa's prediction.

http://dev.physicslab.org/Document.aspx?doctype=3&filename=AtomicNuclear_ChadwickNeutron.xml http://dev.physicslab.org/Document.aspx?doctype=3&filename=AtomicNuclear_BohrModel.xml

At the time, the debate over whether or not atoms were real had almost played out, but the questions surrounding the true nature of the electron were still unanswered. Millikan's oil-drop experiment settled many of these questions by accurately determining (within one part in a thousand) both the charge and, by virtue of the charge-to-mass ratio, the mass of the electron. Both numbers allowed the Danish physicist Niels Bohr to finally calculate Rydberg's constant and provided the first and most important proof of the new atomic theory. http://dev.physicslab.org/Document.aspx?doctype=3&filename=AtomicNuclear_MillikanOilDrop.xml

http://www.robeson.k12.nc.us/cms/lib6/nc01000307/centricity/domain/4951/atomictimeline_project_chemistry.pdf http://www.lz95.org/assets/1/17/history_of_the_atom_project.pdf [] Why is this not a transporter? [] Why is this closer to a transporter? http://www.ibtimes.com/could-star-trek-transporter-be-real-quantum-teleportation-possible-scientists-say-1592171

Someones summary of the discovery of Atomic Theory http://www.chemteam.info/AtomicStructure/AtomicStructure.html

Mars http://www.themarslab.org/app/uploads/2014/05/Project-Mars-Ver2-01.pdf

What is science? How do scientific models and explanations change over time? What happens when observations are found that don't quite fit scientific models or explanations? What is a theory? What is the difference between a theory and a law? Why is atomic theory not a law?

Picture an atom. What does it look like? Most likely it will resemble something like this: a fairly large nucleus surrounded by orbiting electrons whizzing around the nucleus. This image is a popular icon of the atom, but it only vaguely represents our current model of what the atom looks like. First, we are going to travel back a little over 2,000 years ago to the times of Aristotle and Democritus. The Greek philosopher Aristotle believed that matter could be divided infinitely without changing its properties. Democritus disagreed. He thought that matter could only be divided until you got to the smallest particle (which he called the atom, coming from the Greek word //atomos //, meaning //indivisible //). So, who was right? Aristotle was very convincing and did many experiments using the scientific method, so more people believed him. It wasn't until around 2,000 years later, in the early 1800s, when **John Dalton **came along and disproved Aristotle. Dalton went on to say that matter is made up of tiny particles, called atoms, that cannot be divided into smaller pieces and cannot be destroyed. He also stated that all atoms of the same element will be exactly the same and that atoms of different elements can combine to form compounds. The really awesome thing about Dalton's model of the atom is that he came up with it without ever seeing the atom! He had no concept of protons, neutrons or electrons. His model was created solely on experiments that were macroscopic, or seen with the unaided eye. Now, let's fast-forward to the late 1800s when **J.J. Thomson ** discovered the electron. Thomson used what was called a **cathode ray tube **, or an electron gun. You've probably seen a cathode ray tube without even knowing it! They are the bulky electronic part of old television sets. Thomson used the cathode ray tube with a magnet and discovered that the green beam it produced was made up of negatively charged material. He performed many experiments and found that the mass of one of these particles was almost 2,000 times lighter than a hydrogen atom. From this he decided that these particles must have come from somewhere within the atom and that Dalton was incorrect in stating that atoms cannot be divided into smaller pieces. Thomson went one step further and determined that these negatively charged electrons needed something positive to balance them out. So, he determined that they were surrounded by positively-charged material. This became known as the 'plum pudding' model of the atom. The negatively charged plums were surrounded by positively charged pudding.

A few years later, **Ernest Rutherford **, one of Thomson's students, did some tests on Thomson's plum pudding model. The members of his lab fired a beam of positively charged particles called alpha particles at a very thin sheet of gold foil. (Later on you will learn that alpha particles are really just the nuclei of helium atoms.) Because these alpha particles had so much mass, he fully expected that all of the alpha particles would go right through the gold foil. This is because, if Thomson were correct about the plum pudding model of the atom, the alpha particles would just go through the positively charged matter and hit the detecting screen on the other side.

But something strange happened. Some of the alpha particles went through, and some were deflected by the gold foil and hit the detector in different locations. Some even came straight backwards in the same exact path that they took! Rutherford said this would be as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. After this experiment, Rutherford concluded that these alpha particles must have hit something very small, dense and positively charged in order for them to come straight back. Rutherford claimed that this also shows that the atom consists mostly of empty space and that all the positive charge is not evenly spread throughout the atom but instead squished into a teeny tiny nucleus in the center of the atom.  <span style="background-color: #ffffff; color: #2b2b2b; display: block; font-family: Roboto,sans-serif; text-align: justify;"> 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. In 1920, Ernest Rutherford postulated that there were neutral, massive particles in the nucleus of atoms. This conclusion arose from the disparity between an element's atomic number (protons = electrons) and its atomic mass (usually in excess of the mass of the known protons present). **James Chadwick** was assigned the task of tracking down evidence of Rutherford's tightly bound "proton-electron pair" or neutron. <span style="background-color: #ffffff; color: #2b2b2b; display: block; font-family: Roboto,sans-serif; text-align: justify;"> 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. However, unlike gamma rays, these rays did not discharge charged electroscopes (the photoelectric effect). Irene Curie and her husband discovered that when a beam of this radiation hit a substance rich in protons, for example paraffin, protons were knocked loose which could be easily detected by a Geiger counter.

In 1932, Chadwick proposed that this particle was Rutherford's neutron. In 1935, he was awarded the Nobel Prize for his discovery. Using kinematics, Chadwick was able to determine the velocity of the protons. Then through conservation of momentum techniques, he was able to determine that the mass of the neutral radiation was almost exactly the same as that of a proton.

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<span style="background-color: #ffffff; color: #2b2b2b; display: block; font-family: Roboto,sans-serif; text-align: justify;"> <span style="background-color: #ffffff; color: #2b2b2b; display: block; font-family: Roboto,sans-serif; text-align: justify;"> These were just a few of the hundreds of scientists that worked hard to further our knowledge and understanding of the atom. It is important to note that our understanding has been an evolving process, including Aristotle and Democritus' opposing views of the atom. Aristotle believing matter could be divided forever, and Democritus believing that we would eventually get to the smallest particle, called the atom. Two thousand years later, Dalton proved Democritus was correct. Shortly after that, electrons were discovered by Thomson, the nucleus was discovered by Rutherford and the charge of an electron was measured by Millikan. The picture of the atom you had when this lesson started is still flawed when compared to the current view of the atom, which we will discuss in a future lesson. And as scientists uncover more details about the atom, the model we use to describe it will change and become more and more accurate.