Nuclear Chemistry Study Guide: C19.1 & C19.3

1. Basics of Nuclear Chemistry

• Nucleus: The dense center of an atom, contains protons (+) and neutrons (neutral).

• Proton: Positive charge, ~1 amu.

• Neutron: Neutral, ~1 amu.

• Electron: Negative charge, negligible mass.

• Atomic Number (Z): Number of protons → defines element.

• Mass Number (A): Protons + neutrons.

• Isotope: Same number of protons, different number of neutrons.

Check: Can you find protons, neutrons, electrons for any atom/isotope?

2. Nuclear Stability

• Atoms are unstable if nucleus has too many or too few neutrons compared to protons.

• Unstable nuclei emit radiation (particles & energy) to become more stable.

Factors affecting stability:

• Ratio of neutrons to protons

• Size of the nucleus (larger nuclei are more likely to decay)

3. Types of Radiation

Key:

• Alpha decay → daughter nuclei are different elements, a type of fission reaction.

• Beta decay → neutron → proton + electron; changes element.

• Gamma decay → pure energy, no particle emission, often follows alpha/beta decay.

4. Nuclear Reactions

• Nuclear Process: Involves change in the nucleus (protons/neutrons) → releases much more energy than chemical reactions.

• Total nucleons (protons + neutrons) are conserved, but element may change.

Fission

• A large nucleus splits into smaller nuclei + energy + neutrons.

• Example: Uranium-235 + neutron → Barium-141 + Krypton-92 + 3 neutrons + energy

• Fragments have fewer protons than original nucleus.

• Used in nuclear reactors and atomic bombs.

Fusion

• Two small nuclei combine to form a larger nucleus + energy.

• Example: Hydrogen isotopes → Helium + energy (sun & hydrogen bombs).

• Resulting nucleus has more protons than either original nucleus.

• Requires high temperatures and pressures.

Energy:

• Both processes release or absorb energy; huge compared to chemical reactions.

5. Radioactive Decay & Half-Life

• Spontaneous nuclear reaction → unstable nucleus emits particle/energy.

• Daughter nucleus: Product of decay.

• Half-life (t½): Time it takes for half of a radioactive sample to decay.

  • Can calculate remaining atoms:

    N=N0(12)t/t1/2N = N_0 \left(\frac{1}{2}\right)^{t/t_{1/2}}

• Energy released can be kinetic (moving particles) or electromagnetic (gamma).

6. Vocabulary Connections

• Absorption: Nucleus absorbs energy → may trigger fusion/fission.

• Particle Emission: Release of alpha, beta, or other particles.

• Nuclear Reactor: Device for controlled fission to produce energy.

• Nonionizing Radiation: Radiation that doesn’t remove electrons (opposite of alpha, beta, gamma).

• Nuclear Mass: Mass of the nucleus, slightly less than sum of parts (mass defect → energy release).

7. Quick Comparisons