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

\

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

\

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

\

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

\