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History of Atomic Theory

History of Atomic Theory. Figuring Out Atoms. Dalton’s Atomic Theory. Matter is composed of extremely small particles called atoms. Atoms are indivisible and indestructible. Atoms of a given element are identical in size, mass, and chemical properties. Dalton’s Atomic Theory.

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History of Atomic Theory

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  1. History of Atomic Theory Figuring Out Atoms

  2. Dalton’s Atomic Theory • Matter is composed of extremely small particles called atoms. • Atoms are indivisible and indestructible. • Atoms of a given element are identical in size, mass, and chemical properties.

  3. Dalton’s Atomic Theory • Atoms of a specific element are different from those of another element. • Different atoms combine in simple whole-number ratios to form compounds. • In a chemical reaction, atoms are separated, combined or rearranged.

  4. Dalton’s Model Atoms are the smallest division of matter. They cannot be divided.

  5. Modern Advancements It wasn’t until almost 80 years after Dalton’s theory that we saw further discoveries. http://www.animatedgif.net/clockscounters/clockscounters4.shtml

  6. J.J. Thomson and the Cathode Ray Tube

  7. J.J. Thomson and the Cathode Ray Tube • Some sort of particles were hitting the Zinc-Sulfide coating • If you bring a magnet towards the beam, the beam moves (towards the positive and away from the negative) • These particles were in all sorts of elements

  8. J.J. Thomson and the Cathode Ray Tube • These small particles are now called electrons. • Thomson designed a new model of an atom by changing Dalton’s model. • This model is called the plum pudding model. http://reich-chemistry.wikispaces.com/Fall.2008MMA.Riley.Timeline

  9. Plum Pudding Model A uniformly positive atom with small negative particles mixed in

  10. Rutherford’s Gold Foil Experiment To test the plum pudding model, Ernest Rutherford designed a simple experiment. http://www.daviddarling.info/encyclopedia/R/Rutherfords_experiment_and_atomic_model.html

  11. Rutherford’s Gold Foil Experiment

  12. Rutherford’s Conclusions • Each atom has a small, dense nucleus • Most of the atom is empty space • Within the nucleus are particles that have a positive 1 charge. He called these particles protons. • He was able to improve the plum pudding model

  13. Rutherford’s Model Small, dense, positively charged nucleus with smaller negative charges surrounding it.

  14. Last Piece of the Puzzle • One of Rutherford’s colleagues, James Chadwick discovered that there must be another particle in the nucleus. • This particle is the same mass as a proton but does not have a charge. • He called these particles neutrons. http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html

  15. Atomic Particles So now we know…. • Electrons are small, negatively charged particles • Protons are positively charged particles in the nucleus • Neutrons are neutral particles in the nucleus

  16. Atomic Structure

  17. Atomic Structure • In the nucleus there are two types of particles: Protons and Neutrons • Around the nucleus there are electrons http://www.theo-phys.uni-essen.de/tp/ags/guhr_dir/research.php

  18. Practice • The number of protons determines the element • How many protons are in each of the following elements? • He: • F: • Ga: • Be: • The number of electrons = the number of protons

  19. Periodic Table Atomic Number = Number of Protons or Number of Electrons

  20. Elemental Notation • Rather than writing out the element’s information each time, we use a special notation to organize information. • Mass Number • Atomic Number • Elemental Symbol

  21. The Numbers • The mass number of an element is the number of protons+ neutrons. • The atomic number of an element is the number of protons the element has. • To find the number of neutrons, subtract the atomic number from the mass number. Rn 222 Mass Number 86 Atomic Number 136 Element Symbol Number of Neutrons

  22. 11 6 12 6 13 6 14 6 C C C C Isotopes • Isotope- Atoms with the same number of protons but different number of neutrons. • Atoms of the same element have the same number of protons • Atoms of the same element can have different numbers of neutrons

  23. Ions • In the nucleus there are protons and neutrons • Protons are positive • Neutrons are neutral • If the nucleus has 3 protons it has a charge of 3+

  24. Neutral Atom In a neutral atom, there are equal numbers of protons and electrons Each positive is cancelled by a negative.

  25. Ions • In an ion, there are unequal numbers of protons and electrons 3 + charge 4 – charge 1 – charge

  26. Ions • In an ion, there are unequal numbers of protons and electrons 3 + charge 2 – charge 1 + charge

  27. What is the charge of an ion that has 29 protons and 32 electrons?

  28. What is the charge of an ion that has 12 protons and 13 electrons?

  29. What is the charge of an ion that has 54 protons and 52 electrons?

  30. Modern Model Finding out more about atoms

  31. Do Now Get one of each paper Keep your homework Complete the do now on your notes page!

  32. What we know… • We know that there are protons, neutrons and electrons. • Protons and Neutrons are in the nucleus. • The nucleus has a positive charge. • Electrons are in the space around the nucleus. • But scientists were learning more about the behavior of atoms while they were studying light.

  33. Photoelectric Effect • Scientists continued to explore the properties of matter and light. High Energy Low Energy

  34. Properties of Light • Studies showed that light behaved as packages of energy. • We call these packages photons. Low Energy High Energy

  35. Photoelectric Effect Experiment: Shining light on a piece of metal With low energy photons, no electrons are removed. e- e- e- e- e- e- e- e-

  36. Photoelectric Effect Experiment: Shining light on a piece of metal With many low energy photons, no electrons are removed. e- e- e- e- e- e- e- e-

  37. Photoelectric Effect Experiment: Shining light on a piece of metal With high energy photons, electrons are removed. e- e- e- e- e- e- e- e-

  38. Niels Bohr • Bohr reviewed these results and came up with a new model of the atom. • If only certain types of energy could remove electrons, he thought maybe there were energy levels for electrons.

  39. Bohr’s Model e-

  40. Bohr’s Model e-

  41. Bohr’s Model • This idea of energy levels in an atom were represented by rings.

  42. Bohr’s Model • In the first energy level there are two electrons. e- e-

  43. Bohr’s Model • In the second energy level there are 8 electrons. e- e- e- e- e- e- e- e-

  44. Bohr’s Model • In the third energy level there are 18 electrons. e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-

  45. Energy With Rings • Electrons in the outer rings have more energy than those in the inner rings High Energy Low Energy

  46. Electron Configuration • On our periodic table, the electron levels are represented by the electron configuration. Fluorine: 2-7 Boron: 2-3

  47. Electron Configuration • What is the electron configuration for the following elements? • Oxygen (O): • Beryllium (Be):

  48. Drawing Bohr’s Model Fluorine

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