Matter, Atoms, and Quantum Theory

• Matter occupies volume and has mass
• Matter is composed of particles
• Particles are organized into atoms, molecules, and compounds
• Atoms contain three subatomic particles; electrons, protons, and neutrons
  • Electrons
    • Mass is 0.0005485712 u
    • Electrical charge is 1-
    • Located outside the nucleus
  • Protons
    • Mass is 1.00727252 u
    • Electrical charge is 1+
    • Located in the nucleus
  • Neutrons
    • Mass is 1.008665 u
    • Electrical charge is 0
    • Located in the nucleus

Quantum Theory

• Regarded as the new frontier in matter knowledge
• Physics and Chemistry became entwined at the turn of the century
• Study of matter and energy became the focus of the scientific community
• Light energy became the primary research point
• The question to answer was whether light travels as a particle or a wave
• A lot of evidence and mathematical models support the wave theory of light

The Photoelectric Effect

• In 1887, Heinrich Hertz, a German physicist, discovered the photoelectric effect while attempting to generate electromagnetic waves using induction coils
• Photoelectric effect happens when light shines on a metal surface leading to the emission of electrons from the metal
• This was discovered when Hertz hooked up charged zinc to an electroscope and exposed the zinc to UV light, which reduced the charge on the electroscope

Max Planck and Blackbodies

• Max Planck, a german physicist, was studying blackbodies (objects that absorb and radiate light) in 1900
• Planck studied the energy emitted from blackbodies when they are heated to incandescence, or glowing
• Solids emit light when heated to high temperatures.
  • Emitted light first appear red, then white, then blue
  • When a stove element is turned on will soon emit heat (IR radiation) and red light
• The light intensity of different colors can be measured and plotted on a graph, creating an energy curve
• Classical physics predicted that the energy curve should go up continuously as temperature increases
• Planck's experiments showed the curve reached a peak and then decreased

Planck's Quantum Hypothesis

• Planck accounted for the unexpected results by hypothesizing that matter can gain or lose energy only in whole-number multiples
• He stipulated that light release isn't constant and that happens in bursts rather than as a continuous stream
• One burst or packet of energy is now known as a quantum of energy
• Energy transfer is like working on a staircase rather than a ramp
• Energy is quantized or restricted to specific levels
  • This is like how climbing a ladder must be done using rungs
  • You cannot step between rungs to climb
• Energy is not continuous
  • Like climbing a ramp, you can stop at any point
  • A ramp does not have discreet or specific values, like energy

Einsteins additions

• Einstein explained the photoelectric effect in 1905 by applying Planck's idea of a quantum of energy
• Concluded that the size of a quantum of EM energy depends on its frequency causing one photon of energy to eject one electron
• Refined the terminology of quantum to photon
• Electromagnetic radiation is viewed as a stream of particles called photons
• Photon = A unit of light energy
• If a single electron absorbs a single photon with the right quantity of energy, the electron is able to escape the metal surface
• If a photon doesn't have enough energy, no electrons can escape the metal no matter how many photons strike it The electron remains in place due to electrostatic forces Einstein received a Nobel Prize in 1921 for his paper explaining the photoelectric effect in terms of quantum theory

Overview of matter and its composition, discussing atoms, molecules, and compounds. Details the subatomic particles: electrons, protons, and neutrons, including their properties. An introduction to quantum theory and the photoelectric effect is provided.