Unit 2 - Understanding the Atom

The Historical Development of Atomic Theory

  • Democritus - Early philosopher who proposed the existence of the atom
  • Dalton’s Atomic Theory   * First scientific theory of the atom   * Based on Joseph Proust and other scientists’ research     * Proust’s research: each compound contains exact proportions       * Law of definite proportions   * Atoms are indivisible   * Elements are made of identical atoms unique to each element   * Compounds are made of 2+ atoms in fixed proportion   * A chemical reaction is the rearrangement of atoms
  • Discovery of the Electron (Cathode Ray Experiment)
  • By JJ Thompson
  • Led to the Plum Pudding Model
  • Oil Drop Experiment   * By Millikan     * Thompson found charge & mass of electron
  • Discovery of Nucleus (Gold Foil Experiment)   * By Rutherford   * Most particles pass directly through the atom, some get deflected   * → Most of the atom is empty space, with a large particle at the center
  • Quiz: https://quizizz.com/admin/quiz/5faee2a376564d001b6fb43a/the-historical-development-of-atomic-theory

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Electromagnetic Waves

  • Vocab   * Electric Field - The area surrounding a charged object in which it can act upon another charged object   * Electromagnetic Spectrum     * The frequency spectrum containing all electromagnetic waves     *   * Electromagnetic Wave     * A combination of electric & magnetic fields radiating from a source @ the speed of light.       * The electric & magnetic fields oscillate perpendicular of each other     * Caused by disturbing charged particles, which then oscillate and produce oscillating fields       * Source produces an magnetic field, the magnetic field then produces an electric field, the electric field the produces another magnetic field, repeat forever   * Magnetic Field - The area surrounding a magnetic object in which it can act upon an object   * Polarization
  • Types of Waves   * Mechanical - Waves that use matter to carry energy   * Electromagnetic - Waves that do not use/need matter to carry energy     * Are all transverse waves
  • Parts of a Transverse Wave   * Crest - Midline → Top   * Trough - Midline → Bottom   * Amplitude - Top → Midline or Midline → Bottom   * Wavelength - Crest 1 → Crest 2   * Frequency - Oscillations per second   *
  • Electromagnetic Waves   * Each type is contained on a different part of the electromagnetic spectrum     * High frequency/low wavelength → low frequency/high wavelength:       * Gamma Rays → X-Rays → Ultraviolet → Visible Light → Infrared → Microwaves → Radio waves   * Energy transferred     * Energy = plank’s constant * frequency       * Plank’s constant ~ 6.63 * 10^-34   * Frequency, Wavelength, & Speed     * Speed of light = frequency(hertz) * wavelength(meters)     * Slower = Smaller wavelength   * Uses     * Gamma Rays - Used to destroy cancer cells     * Ultraviolet Rays - Disrupts DNA production in bacteria & viruses     * X-Rays - Used for medical imaging     * Infrared - Heat lamps, remote controls     * Microwaves - Warm food     * Radio waves - Long distance transmission of information   * Polarization - Modifying light by forcing it to only vibrate in a singular plane

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The Modern Atomic Theory

  • Theories of Light   * Newton - Corpuscular theory; light is made of particles   * Thomas Young - Diffraction double slit experiment; light behaves like waves   * Heinrich Hertz - Photoelectric effect observed; also acts like a particle
  • Photoelectric Effect   * Electrons are emitted when electromagnetic waves hit a material   * Shows particle like behavior     * Einstein proposes light is a stream of particles called photons       * Energy = Plank’s constant * frequency
  • Emission Spectrum   * Visible light spectrum where emitted light produce colored bands   * Some metals showed up as discrete lines
  • Bohr Model   * Electrons orbit nucleus made of protons & neutrons
  • Electron Cloud Model   * Electrons have probable locations   * Each cloud has different energy levels

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The Structure of the Atom

  • Atom - Smallest particle of a substance   * Made of a nucleus surrounded by orbitals   * Consists of 3 types of particals     * Protons - Positively charged     * Neutrons - Particle w/o charge     * Electron - Negatively charged electron   * Charge of proton = negative charged of electron     * If charge of atom = 0, then the atoms has == number of protons & electrons   * Locations     * Nucleus - Contains all the protons & neutrons     * Orbitals - Contains the electrons
  • Atomic mass unit   * 1/12 of a C12 atom   * ~ 1.660538921 * 10^-24 g   * Proton - 1 amu   * Neutron - 1 amu   * Electron - 0.0006 amu
  • Atomic Number   * \     # of Protons in an atom
  • Ions   * Charged atoms   * Changed number of electrons
  • Atomic Mass / Mass Number   * \     # of Protons + # of Neutrons
  • Isotopes   * Different # of neutrons

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