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.