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.
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.
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 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.
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).
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.
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.
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.