Austin Klasner Mrs. Garner Adv. Chem I October 16th, 2014 Atomic Theory Throughout our history, we have always questioned the way things work and why they do so. The same goes for matter, what is it made of? How can you rearrange it? The answer - Atoms. Throughout history, atoms have been questioned and reimagined, experimented with, and even split. But how did we discover these tiny building blocks of nature? It all begins with a greek philosopher a some questions. Democritus - a greek philosopher - was born in 460 BC. He was known as the laughing philosopher because he viewed simpler minded people as comical. His views on the atom began when he questioned how something could come from nothing and came to the conclusion that this must be impossible. He held that nothing could come from nothing(Democritus, 1). He believed that all the matter that will ever exist in the universe already does exist but it is just a matter of combining and recombining “eternal bits of stuff”. He named these “eternal bits of stuff” atoms. (Democritus, 1) A long time passed before any more research really began. It wasnt until John Dalton in the 1800s that any research was really done at all on the scientific topic of atoms. John Dalton, a scientist who also discovered color blindness, came up with an atomic theory. In the 1780s, Lavoisier ushered in a new chemical era in the field of science. This new need of chemical research allowed compounds and the recompisition of compunds to be meausered more accurately than ever. This new ability of measuring compounds and their recompostion allowed scientist John Dalton to research into compunds further than he previously could (Dalton 1). In 1803, Dalton noticed while researching oxygen and carbon compunds that the ratios in two compunds of the elements is that one had a ratio of 1.33 to 1 and the other compoiund had a ratio of 2.66 to 1. Discovering this lead Dalton to prupose the law of multiple proportions. This law caused other scientists to research how elements could combine with eachother and the patterns in which they did combine (Dalton 1) Daltons Atomic Theory was different from Democritus thoughts on the atom because Dalton had much more research. Technology, and accuracy to work with. Daltons Atomic theory had four parts to it. 1-All matter is made of atoms. Atoms are indivisible and indestructible. 2- All atoms of a given element are identical in mass and properties. 3-Compounds are formed by a combination of two or more different kinds of atoms. 4- A chemical reaction is a rearrangement of atoms (Dalton, 1). The next big discovery about the atom didnt come until 1894, where J.J. Thomson used cathode rays to discover the electron. Cathode rays are light rays inside of a high-vaccum tube.Thomson placed gases in the tube between the cathode end (-) to the anode end (+). The particles were deflected when passed through the tube. Thomson measured the ratio of the charge of the particles and the angle of the ray. No matter what gas was used, the ratio was the same. This meant that the particles used to make up the gases were universal. (J.J. Thomson, 2) Through the cathode ray tube experiment, Thomson discovered that there were particles much smaller than atoms that composed all matter. He had discovered the electron. In 1906, Thomson also discovered isotopes. He shot a stream of neon through a magnetic field and discovered two different mass to charge ratios, realizing that neon was made p of two different kinds of atoms. This proved the existence of isotopes in stable elements (J.J. Thomson, 2). Thomson also created a new atomic model with this new discovery. He named it the “plum pudding model”. The model consisted of a ball of pudding (positive charge) that the plums (negative electrons) sat in. This was the first model of an atom that was anything other than just a ball of unknown particles as the atom. In 1909, Robert Millikan did an experiment to determine the size of the charge on an electron.”What Millikan did was 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 was able to work out the mass of the oil drop, and he could calculate the force of gravity on one drop, he could then determine the electric charge that the drop must have”(Millikan, 1). The charge of the electron was negative. Millikan discovering the charge of the electron allowed scientists to do many more experiments regarding the makeup of an atom, including Ernest rutherford just a year after this discovery. In 1910, Ernest Rutherford performs the “gold foil experiment”. His purpose was to find out the structure of the atom. Rutherford accepted Thomsons “plum pudding” model. In this experiment, rutherford shoots a constant beam of pure positive alpha particles (helium atom particles) into a thin sheet of gold foil. The gold foil had a small hole in the center where the beam would shoot through into a fluorescent screen which would recieve the alpha particles. (Rutherford, 1) The Way the experiment worked is that there were is the alpha particles that were shot into the extremely small hole. Most of the alpha paricles were shot through the hole and reached the fluorescent screen on the other side. Some of the alpha particles were deflected and hit other places on the fluorescent screen. This means that there was mostly empty space in the atom since most alpha particles passed through the slit. This also means that the alpha particles were hitting a positively charged region because they were being deflected and positive repels positive. Because the number of alpha particles being deflected was a relatively small amount, the size of the atom must be small compared to the size of the entire atom. The alpha particles, which are dense, were deflected by this center region of the atom,. This means that most of the mass of the atom is in this center region. (Rutherford, 2) With new information aquired, a new atomic model was needed. Rutherfords atomic model, or the “planetary model”, included this empty space and densely packed pocitive center. The empty space was where the electrons were placed. The electrons orbited on a select track. The dense center was named the nucleus of the atom. It is where the positive charge came from and where most of the mass came from, and it was very small compared to the total size of the atom. (Rutherford, 3) In 1932, James Chadwick becomes Rutherfords assistant. After Rutherfords discovery of a positive center and electrons orbiting, people knew that atoms were nuetral. Knowing this, they believed that half the electrons were outside of the nucleus orbiting, and the other half were in the center packed with the positive particles. James Chadwick wanted to study the nucleus further. ( James, 2) At this time, some scientists believed that no-charge particles could possibly exist. These scientists include both Chadwick and Rutherford. Throught the 1920s, Chadwick composed several experiments in an attempt to find these nuetrally charged particles, but he was without success. Chadwicks luck finally struck when heard of two scientists in Paris. The scientists thought that they had managed to eject protons from wax using gamma rays. The gamma ray source was a radioactive element called polonium. (James, 3) Chadwick believed that the gamma rays were actually nuetrons. He began working to replicate the experiment in the Cavendish laboratory. He used the radioactive element as his source of nuetrons and shot wax with the polonium. The experiment behaved exactly as it had in the Paris lab. The protons were released from the wax and Chadwick began running measurements. Chadwick realized that the protons reacted exactly the same as if they were hit by nuetral particle. He had finally discovered the nuetron. (James, 3) Today, the way we view the atom is slightly different from that of Thomsons or Rutherfords models. Todays atomic model consists of an electron cloud filled with few electrons and a lot of empty space. It also has a nucleus consisting of protons in the same number of the amount of electrons. The amount of nuetrons can be changed to create isotopes of the same element. Although some of Daltons laws were proved wrong or slightly incorrect, they were still an important part of our atomic science history. None of our modern day atomic science could be possible without the work of these six men. Democritus, who came up with the theory of the atom. Dalton, who proposed laws that the atoms must have followed. Thomson, who discovered the electron. Millikan, who discovered the charge of the electron. Rutherford, who discovered the nucleus. And Chadwick, who discovered the Nuetron. Works Cited egs.edu/library/democritus/biography/ dl.clackamas.cc.or.us/ch104-04/daltons.htm biography/people/jj-thomson- ffden-2.phys.uaf.edu/212_fall2003.web.dir/Ryan_McAllister/Slide3.htm physics.tutorvista/modern-physics/rutherford-s-gold-foil-experiment.html famousscientists.org/james-chadwick/
Posted on: Mon, 20 Oct 2014 06:04:54 +0000
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