The Atomic Nucleus

The Atomic Nucleus

Nuclear Size and Density:

  • Very small compared to atomic size
  • Very dense, contains most of the atom’s mass

Nuclear Composition:

  • Protons: Positively charged particles, determine the element’s identity *Symbol: p or + *Charge: +1
  • Neutrons: Uncharged particles, contribute to the atom’s mass *Symbol: n or 0 *Charge: 0
  • Protons and neutrons are collectively called nucleons

Nuclear Force:

  • Strong nuclear force:
    • Overcomes electrical repulsion between positively charged protons.
    • Very strong over short distance, but rapidly diminishes with increasing distance

Models of the Atomic Nucleus:

  • Rutherford Model:
  • Early model proposed by Rutherford.
  • Depicted the nucleus as a small, dense, positively charged core surrounded by electrons.
  • Liquid Drop Model:
  • Compares the nucleus to a drop of incompressible liquid.
  • Used to describe nuclear fission and fusion.
  • Shell Model:
  • Describes the nucleus as having specific energy levels or shells for protons and neutrons, similar to electron shells.

Radioactivity:

  • The spontaneous emission of particles or energy from an unstable nucleus to achieve a more stable state.
  • Types of radioactive decay:
    • Alpha decay (α)
    • Beta decay ( β)
    • Gamma decay ( γ)

Nuclear Reactions:

  • Nuclear fission:

    • Heavy nucleus splits into smaller nuclei, releasing a large amount of energy.
    • Used in nuclear power plants and atomic bombs.
  • Nuclear fusion:

    • Two or more light nuclei combine to form a heavier nucleus, releasing a large amount of energy.
    • Powers the sun and stars.
  • Chain reactions:

    • When neutrons released from a nuclear reaction cause further nuclear reactions, creating a self-sustaining chain.

Applications of Nuclear Physics:

  • Nuclear power: Generation of electricity through controlled nuclear fission reactions.

  • Radioactive isotopes: Used in medicine (e.g., cancer treatment), industry, and research (e.g., carbon dating).

Stability of the Nucleus:

  • Neutrons play a crucial role in stabilizing the nucleus, especially for elements with a high number of protons.

  • Nuclear Binding Energy: Energy required to separate all nucleons in a nucleus, a measure of nuclear stability. The more tightly bound the nucleons, the more stable the nucleus.

The Mass Defect:

  • The difference between the mass of an atom’s nucleus and the sum of the masses of its individual nucleons.
  • Mass defect is converted into energy according to Einstein’s famous equation, E=mc².


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