Discovery of the atom


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Discovery of the atom

  2. 2. Ancient Greek Philosophies of the Element<br />In Greece 530 B.C a philosopher Thales, made his philosophy that the fundamental “element” is water.<br />Aristotle 200 years later around 300 B.C adjusted this philosophy to: <br />Earth- Which is cold and dry<br />Air- Which is hot and wet<br />Fire- Which is hot and dry<br />Water- Which is cold and wet<br />Aether- Which make up the heavens (space, stars and planets)<br />This philosophies was practically embedded into the mind of man for almost two thousand years. With no one apposing the philosophy until the mid seventeenth century.<br />
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  4. 4. Robert Boyle<br />In the mid seventeenth century an Irish Chemist by the name Robert Boyle wrote a book that is taught to the creation of modern chemistry. <br />The book was named “ THE SCEPTICAL CHEMYST”. <br />In this book Boyle questioned the philosophy of the ancient Greeks that states that earth, air, water, fire, and aether were the fundamental “elements”. <br />Also he suggested that “the scientific approach to theories”. This is that before a theory accepted experiments must be carried out to prove the theory correct. However no one headed this until two hundred years later.<br />
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  6. 6. John Dalton<br />In the year 1803 a English scientist, John Dalton came up with the Dalton Atomic theory after years of studies and gathering of useful information. This stated that:<br />Matter is made up of atoms<br />Atoms are indivisible<br />Atoms cannot be destroyed<br />All atoms of the same elements are identical<br />Atoms of different element have different mass and chemical properties.<br />Atoms of different elements combine to form compounds.<br />Although now some of these theories are proven wrong, Dalton theories are still recognized as a foundational since it allowed for other scientist to follow in his footsteps after his time.<br />
  7. 7. J.J Thompson<br />Sir J.J Thompson an English Physicist is know for the first model of the atom. This is know as the Plum Pudding Model. He proposed the atom contained both positively charged particles and negatively charged particles moving very rapidly and randomly. <br />He came up with this theory after experimenting with cathode rays. The experiment showed that a cathode ray was easily deflected by and electric field. Being attracted to the positive terminal of anode that was creating the field. This concluded that the ray was made up of negatively charged particles.<br /> He named these particles “Corpuscles” but later changed it to Electrons. <br />
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  9. 9. Earnest Rutherford<br />In 1909, Ernest Rutherford an English Physics came up with his planetary model of the atom, which describes that an atom is similar to the solar system, with the positive nucleus to the center and negative electrons orbiting around it. This statement was made after the experiment put together by Ernest Marsden and Hans Geiger. So far this is was the closest model of the atomic model used today.<br />
  10. 10. The Hans Geiger and Ernest Marsden Experiment<br />In 1909 Hans Geiger and Ernest Marsden supervised by Ernest Rutherford tested J.J Thompsons theory by bombarding a gold foil with alpha particles. Around the foil a screen with zinc sulphate was place, this was to deduce where the alpha particles landed after penetrating the gold foil, since the area where alpha particles hit the gold foil will glow. It was expected that most of the particles were to be slightly deflected. From the random dispersal of positive and negative charges.<br />
  11. 11. The Hans Geiger and Ernest Marsden Experiment<br />However the results suggested other wise. <br />It was found that most of the alpha particles penetrated the foil without deflection, some were deflected only a little and few, about 1 in every 8000 was deflected almost 180°. These results question the plum pudding model by J.J Thompson. <br />Rutherford stated that the atom was not a sphere in which the positive and negative charges are moving about randomly as J.J Thompson stated but rather, the atom is mostly space with a centre that contains a positive charge, which he named Protons and the electrons are orbiting around this charge like the planets orbiting the sun in a solar system.<br />
  12. 12. The Geiger Marsden Experiment<br />
  13. 13. Henry G.J Mosley<br />Henry Gwyn Jeffrey Mosley an English Chemist and Physicist is who like Hans Geiger and Ernest Marsden also studied under Rutherford. It is him who changed out look at the atomic number from just arbitrary but had a specific value. This break through allowed Mosley to arrange elements numerically in the periodic table bases on ascending atomic value.<br /> Sadly Mosely never received a Nobel Prize for this break through since he died in battle during World War 1.<br />
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  15. 15. James Chadwick<br />In 1918 James Chadwick, while working with Ernest Rutherford, was baffled why an atoms mass was much more than the atomic number, e.g. the mass of helium (He) was 4 while the atomic number was 2. Rutherford then proposed that there must be an a particle with the same mass of a proton but with a neutral charge, Rutherford named this particle the Neutron. However there was no way of proving this theory. 14 years later Chadwhik was able to prove that the Neutron is indeed real.<br />
  16. 16. In 1932, after 14 years of tracking this unique particle ( it was tricky to find the neutron at that time since technology at the time only was used only to find charged particles). It was the discovery of gamma rays that allowed for Chadwick’s experiment. <br />Chadwick bombarded a sample of Berrilium with alpha particle which caused the emittion of a mysterious Ray, this Rays was then focused through an electric field and then hit a Geiger counter( A device that measures radiation).<br />
  17. 17. The results of this experiment were:<br />The ray was not affected by an electric field.<br />They did not invoke photons ( this is when an electromagnetic ray like gamma rays strike a surface it discharges electrons which can be easily measured) <br />The Ray caused Protons to be discharged.<br />
  18. 18. James Chadwick<br />From these results Chadwick was able to prove the existence of the Neutron.<br />Chadwick then adjust the atomic model at the time, to the one that is still used today. With the nucleus at the centre containing both Protons and Neutrons and the electrons orbitingg in outer areas<br />apparatus used in experiment<br />
  19. 19. apparatus used in experiment <br />
  20. 20. Modern atomic model or Chadwick’s atomic model<br />
  21. 21. CONCLUSION<br />Although today it is know that there is more particles that make up the protons and neutrons. The scientist seen here were the one’s that discovered the most vital part of science today. Without these founding father’s of chemistry and physics, who knows where we of been today.<br />
  22. 22. THE END!!<br />