Lesson 6.2 Balancing Nuclear Equations Chem GC Edition

Overview of Nuclear Reactions and Radioactive Decay

  • Important to review nuclear reactions focusing on types of radioactive decay and the particles produced.

Types of Nuclear Decay

1. Alpha Decay

  • Definition: Release of an alpha particle, which is essentially a helium nucleus.

    • Composition: 2 protons and 2 neutrons (Helium, Element 2).

    • Representation:

      • Mass number: 4

      • Atomic number: 2

      • Charge: +2 (no electrons present).

  • Example:

    • Breakdown of Uranium-238 (U-238) into Thorium and an alpha particle.

    • In a nuclear reaction:

      • U-238 → Th + He (4,2)

  • Characteristics:

    • Common in large nuclei; less common in smaller ones (typically not below element 70).

    • Alpha particles are weak and can be stopped by skin; also blocked by paper or clothing.

2. Beta Decay

  • Definition: An electron (beta particle) is ejected from the nucleus, converting a neutron into a proton.

    • Representation:

      • Mass number: 0

      • Atomic number: -1 (electron).

  • Example:

    • Thorium undergoes beta decay, resulting in an element with atomic number +1 and constant mass number.

    • Reaction:

      • Th → Pa + e-

  • Characteristics:

    • Penetrating power is higher than alpha; requires metal foil to shield.

3. Gamma Decay

  • Definition: High-energy photons produced during transitions between energy states in the nucleus, often accompanying alpha or beta decay.

  • Characteristics:

    • Gamma rays are very powerful and damaging but have low penetration distance; thick walls of concrete or lead are needed to shield.

  • Note: Gamma radiation isn't emitted in isolation; it's a byproduct of other decays.

4. Other Forms of Decay

  • Positron Emission:

    • Involves the emission of a positron, which is the antimatter counterpart of an electron (mass number unchanged; atomic number decreases by 1).

  • Electron Capture:

    • Inner orbital electron is captured by nucleus, converting a proton into a neutron.

    • As a result, the mass number remains unchanged.

Summary of Radiation Types

  • Alpha Radiation:

    • Composition: Helium nuclei; very low penetrating power.

    • Shielding: Easily blocked by skin, paper, clothing.

  • Beta Radiation:

    • More penetrating than alpha; requires metal foils to block.

  • Gamma Radiation:

    • Very high penetration power; requires thick materials like lead or concrete to block.

Balancing Nuclear Reactions

  • Key Principle: Conservation of mass (Davy Lavoisier).

    • The sum of mass numbers (and atomic numbers) on reactant side equals that on product side.

  • **Example Reaction Handling:

    • Determine products of decay using mass and atomic numbers to solve for missing elements.

  • Technique to find resultant isotopes after decay.

Applications to Real Problems

  • Alpha Decay Example: Radon-226 undergoing alpha decay, producing a new isotope based on balancing principles.

    • Reaction:

      • 226Ra → (4,2)He + X (solve for X).

  • Fission Reaction Example: Uranium-235 bombardment leading to iodine and yttrium production.

    • Resulting in multiple particles as products (e.g., 2 neutrons).


The reaction for a Radon-224 (Rn-224) atom undergoing beta decay can be written as follows:

[ \text{Rn-224} \rightarrow \text{Po-224} + e^- + \bar{
u} ]

In this reaction:

  • Radon-224 (Rn) emits a beta particle (e-) which is an electron.

  • A neutrino (( \bar{
    u} )) is also released.

  • The daughter nuclide is Polonium-224 (Po-224).

This process involves the conversion of a neutron into a proton within the nucleus, resulting in a new element.