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Discovering the Atom…

Discovering the Atom…. A Process of Discovery From Philosophy to Modern Exploration. Journal. In the first part of this unit we will be exploring the atom. What comes to your mind when I say the word atom?. Lesson Objectives.

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Discovering the Atom…

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  1. Discovering the Atom… A Process of Discovery From Philosophy to Modern Exploration

  2. Journal • In the first part of this unit we will be exploring the atom. What comes to your mind when I say the word atom?

  3. Lesson Objectives • To explore the process that accompanied the composition of the Atomic Theory. • To evaluate the methods used by various contributors. • To develop an understanding of the anatomy of the atom

  4. Deep Thoughts by Democritus • All materials in the world are composed of Atoms and Empty Space. • 400 B.C. • No evidence, just a hypothesis! • This explanation of matter was not accepted.

  5. Atoms: Building Blocks of Matter

  6. Aristotle • Saw matter as being continuous… • 350 B.C. • Composed of “Hyle” • This hypothesis was believed!!!

  7. Whew…they bought it!!! • Aristotle’s hypothesis was adopted and believed for nearly 2200 years!

  8. Philosophy No experimentation No proof Diverging beliefs Acceptance based on popularity. Science Experiments Evidence Converging beliefs Acceptance based on the validity and reproducibility of your experiments. Philosophy vs. Science

  9. A Breakthrough… • In the 1700’s Scientists like Sir Issac Newton began to Question Aristotle’s reasoning! • Still no evidence!

  10. NICE… • In the 1700’s the balance was invented. • Here comes that evidence we wanted…

  11. Dalton Explodes on the scene!!! • Dalton…the keen observer. • Was the first to generate a legitimate hypothesis about the structure of the atom. • HE HAD EVIDENCE TO BACK IT UP!!! • Lavosiere & Proust

  12. From Lavosiere… • Conservation of matter! • When observing a NORMAL chemical reaction in a closed environment, the final mass after the reaction MUST equal the initial mass before the reaction!

  13. From Proust… • Law of Definite Proportions • Elements exposed to one another will combine in small, whole number ratios.

  14. Dalton’s Hypothesis… Five Major Points

  15. Point #1: • All Matter is composed of tiny particles called atoms.

  16. Point #2: • Atoms are the indestructible, they cannot be subdivided, created or destroyed.

  17. Point #3: • All atoms of the same element are identical.

  18. Point #4: • Atoms of each element are unique, they are different from all other elements.

  19. Point #5: • Atoms combine in simple, whole number ratios to form chemical compounds.

  20. Dalton’s Law of Multiple Proportions… • The law of multiple proportions states that with the number of one element held constant, there are more than one compound that can form. • e.g. CO, CO2

  21. The Dawn of the Subatomic Era J. J. Thomson 1897

  22. Thomson’s Research… • Cathode Ray tubes… • Discovered the ray had a negative charge. • Determined the ray was composed of “electrons.” • Determined the mass to charge ratio for the electron.

  23. Dalton’s First Law Falls • Dalton’s hypothesis that claims that the atom is the smallest and simplest form of matter was proved wrong through the experimentation of Thomson and Milliken. • Thomson and Milliken found and named the first subatomic particle…the electron.

  24. Robert Milliken (1903) • American scientist determined the actual magnitude of the charge of an electron. • The charge was -1. • Used his charge and Thomson’s ratio to determine the mass to be 1/1837 mass of hydrogen.

  25. Oil Drop Experiment…

  26. Oil Drop Experiment…

  27. Rutherford’s Crew… Two years of intense discovery! 1912 - 1913

  28. Geiger and Marsden…Gold FoilExperimental Setup

  29. The Fruits of Their Labor • Atom is mostly empty space. • Only 1 of 8000 positively charge particles returned to the source… • What do you think this proved?

  30. The Fruits of Their Labor • Atom is mostly empty space. • Only 1 of 8000 positively charge particles returned to the source… • What do you think this proved? • This proved that the atom was mostly empty space • That the center was small and had a positive charge.

  31. Rutherford’s Publication… • Rutherford theorized that the center held all of the positive charge and that it was very small. • Rutherford also named the positive center the nucleus.

  32. MOOOOOOOseley • Using X-Ray tubes determined that each element had a characteristic wavelength. • The magnitude of the wavelength was directly related to the number of positive particles in its nucleus. • Called the positive particles protons. • Devised the idea of Atomic Number!

  33. The Missing Link…the Neutron! • 1920 – Rutherford first to hypothesize the existence of a third massive particle in the nucleus. • 1930 – Walter Bothe first experimentation. • 1932 – Chadwick repeats Bothe’s experiments and finds definite sign of massive, neutral particles with high energy in the nucleus.

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