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.