Origin of Atoms

Origin of Atoms

  • The universe began approximately 13.8 billion years ago.

  • Initial formation of hydrogen, helium, and lithium atoms occurred within the first 300,000 years after the Big Bang.

  • Clumping of matter eventually led to the formation of stars, which through nuclear fusion created heavier elements.

Nuclear Reactions Overview

  • Transition from discussing chemical reactions to nuclear reactions.

  • Chemical reactions involve electrons: they rearrange atoms without changing the nuclei, hence no creation or destruction of atoms.

  • In contrast, nuclear reactions involve changes in the nucleus, leading to changes in the atomic number of elements.

  • Nuclear reactions typically occur under high temperatures or energies, distinguishing them from chemical reactions.

Atomic Structure

  • An element is defined by the number of protons in its nucleus (atomic number).

  • Notation of nuclear reactions:

    • Atomic number (number of protons) as a subscript on the left.

    • Mass number (number of protons + neutrons) as a superscript on the left.

  • Protons and neutrons are collectively known as nucleons.

  • Example: Potassium has an atomic number of 19.

  • Nitrogen-12 has 7 protons and 5 neutrons (atomic number is 7).

Isotopes

  • Isotopes are variations of the same element with differing numbers of neutrons.

  • Example: Carbon-12 vs Carbon-13.

    • Carbon-12: 6 protons, 6 neutrons.

    • Carbon-13: 6 protons, 7 neutrons.

Types of Nuclear Reactions

  • Fusion: Joining of two light nuclei to form a heavier nucleus (e.g., what happens in stars).

  • Fission: The splitting of a heavier nucleus into lighter nuclei.

  • Radioactive Decay: Process by which an unstable nucleus emits particles (alpha, beta, or gamma).

Fusion Process

  • High temperatures can facilitate fusion:

    • Example: Deuterium (D) and Tritium (T) are isotopes of hydrogen that can fuse.

    • Result of fusion: formation of a helium nucleus, a neutron, and a significant amount of energy.

  • Nuclear equation representation of the fusion reaction captures conservation of nucleons and protons, ignoring electrons.

Energy and Plasma

  • Nuclear reactions release substantial energy, which is harnessed for nuclear power.

  • Understanding of plasma:

    • Plasma is a state of matter containing unbound positive and negative particles.

    • It responds strongly to electromagnetic fields; consists primarily of charged particles.

    • Outnumbering the other states, plasma is especially common in stars where nuclear reactions primarily occur.

Forces in Nuclear Reactions

  • As nuclei approach, they repel due to electrostatic force (both positively charged).

  • Overcoming this repulsion requires significant energy, increasing potential energy.

  • Upon getting very close (nuclear distance), the strong nuclear force can be activated:

    • The strongest fundamental force that operates at short distances, holding the nucleus together.

    • Strong nuclear force acts attractively to bind nucleons, allowing fusion to occur if the kinetic energy is sufficient to overcome the repulsive electrostatic forces.

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