Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atoms and Atomic Theory Day 1: History of the Atom Chemistry Mrs. Kam

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Your group will examine the 3 boxes. Can you figure out a way to determine what is in the box without opening it? Indirect evidence: Chapter 3 Section 1 Substances Are Made of Atoms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives State the three laws that support the existence of atoms. List the five principles of John Dalton’s atomic theory. Chapter 3 Section 1 Substances Are Made of Atoms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Theory The idea of an atomic theory is more than 2000 years old. Until recently, scientists had never seen evidence of atoms. Chapter 3 Section 1 Substances Are Made of Atoms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Theory, continued Chapter 3 Section 1 Substances Are Made of Atoms The figure on the right is a more accurate representation of an atom than the figure on the left.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Brief History of Atomic Theory

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The monster in the cave There once was a monster who lived in a dark cave. You are a knight and have been sent to fight this monster. First, you need to know how big your opponent is. How can you find out the size of this monster (he will not come out of the dark cave). Hint: Lord Ernest Rutherford in the early 1900s used this equation: Hits divided throws= the size of the nucleus (in your case the cave)

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu To Fight the Monster: 1. Cover the eyes of the person rolling the marbles at the monster. 2.Roll the marbles into the box (cave). 3. Move the monster each time it is hit by a marble. 4. Record the number of throws (only marbles that made it into the cave) and the number of hits.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How does this cave monster tie into the discovery of the atom’s nucleus??

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles Rutherford Discovered the Nucleus Thomson proposed that the electrons of an atom were embedded in a positively charged ball of matter. His model of an atom was named the plum-pudding model. Section 2 Structure of Atoms Chapter 3

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Rutherford Discovers the Nucleus, continued Ernest Rutherford performed the gold foil experiment, which disproved the plum-pudding model of the atom. A beam of small, positively charged particles, called alpha particles, was directed at a thin gold foil. Rutherford’s team measured the angles at which the particles were deflected from their former straight-line paths as they came out of the foil. Rutherford found that most of the alpha particles shot at the foil passed straight through the foil. But very few were deflected, in some cases backward. Section 2 Structure of Atoms Chapter 3

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Gold Foil Experiment Chapter 3

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Rutherford Discovers the Nucleus, continued Rutherford reasoned that only a very concentrated positive charge in a tiny space within the gold atom could possibly repel the fast-moving, alpha particles enough to reverse the alpha particles’ direction. Rutherford also hypothesized that the mass of this positive-charge containing region, called the nucleus, must be larger than the mass of the alpha particle. Rutherford argued that the reason most of the alpha particles were undeflected, was that most parts of the atoms in the gold foil were empty space. Section 2 Structure of Atoms Chapter 3

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Gold Foil Experiment on the Atomic Level Chapter 3

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Subatomic Particles, continued Rutherford Discovers the Nucleus, continued The nucleus is the dense, central portion of the atom. The nucleus is made up of protons and neutrons. The nucleus has all of the positive charge, nearly all of the mass, but only a very small fraction of the volume of the atom. Section 2 Structure of Atoms Chapter 3

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Atomic Models Rutherford’s Model Proposed Electron Orbits The experiments of Rutherford’s team led to the replacement of the plum pudding model of the atom with a nuclear model of the atom. Rutherford suggested that electrons, like planets orbiting the sun, revolve around the nucleus in circular or elliptical orbits. Rutherford’s model could not explain why electrons did not crash into the nucleus. The Rutherford model of the atom was replaced only two years later by a model developed by Niels Bohr. Section 3 Electron Configuration Chapter 3