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