Chapter 6: Photon, electron, atom

Key Concepts in Atomic Structure and Applications

Understanding Atoms

  • Basic Definition: All matter consists of tiny particles called atoms or groups of atoms (molecules).

  • Atom Components:

    • Nucleus: The central part of the atom.

    • Electrons: Negatively charged particles that orbit the nucleus.

The Nucleus

  • Structure:

    • Composed of positively charged particles (protons) and neutral particles (neutrons).

  • Charges:

    • Protons provide a positive charge to the nucleus.

    • Example:

    • Helium: 2 protons, 2 neutrons (Net Charge = +2)

    • Carbon: 6 protons, 6 neutrons (Net Charge = +6)

  • Defining Atoms:

    • The number of protons determines the type of atom (e.g., Gold = 79 protons).

  • Binding Force: Strong nuclear force holds protons and neutrons together.

The Electrons

  • Properties:

    • Negatively charged and 2000 times smaller than protons/neutrons.

    • Most of the atom's weight is in the nucleus.

  • Movement: Electrons orbit the nucleus at high speeds (approximately 2200 km per sec) , completing an orbit around Earth in about 18 seconds.

Photons

  • Definition: A photon is a discrete bundle of electromagnetic energy.

  • Movement:

    • Always in motion with a constant speed in a vacuum.

    • Speed of light: c = 2.998 × 108 m/s

Real-World Applications

  1. Atomic Submarine:

    • Powered by nuclear reactors that split atoms to release energy as heat, generating steam to drive propulsion turbines.

  2. X-ray Radiography:

    • Uses photons created from the electron cloud of atoms.

    • Applications:

      • Detects bone fractures, tumors, pneumonia, injuries, and dental problems.

    • Risks: Produces ionizing radiation that can be harmful, with a generally low risk of cancer over time from repeated exposure.

The Electromagnetic Spectrum

  • Categories:

    • Radio Waves, Microwaves, Infrared, Visible Spectrum, Ultraviolet, X-Rays, Gamma Rays.

  • Wavelength and Energy Ranges:

    • Wavelengths vary significantly from radio waves (long) to gamma rays (very short).

    • Energy levels range from lower (radio waves) to higher (gamma rays).

Quick reference

  • Key Terms/Concepts

    • Atom: The basic unit of matter, consisting of a nucleus and electrons.

    • Nucleus: The central part of an atom, containing protons and neutrons.

    • Proton: A positively charged particle found in the nucleus of an atom.

    • Neutron: A particle with no charge, also located in the nucleus.

    • Electron: A negatively charged particle that orbits the nucleus of an atom.

    • Photon: A particle of light that represents a quantum of electromagnetic energy.

Problem-Solving Steps

  1. Identifying the Atom Type:

    • Count the number of protons in the nucleus to determine the element (e.g., gold has 79 protons).

  2. Calculating Net Charge:

    • Use the formula: Net Charge = Number of Protons - Number of Electrons.

    • Example: A neutral carbon atom has 6 protons and 6 electrons, resulting in a net charge of 0.

  3. Understanding Photon Behavior:

    • Recognize that photons travel at the speed of light in a vacuum and are always in motion.