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Balancing Nuclear Equations
To balance a nuclear equation, the mass number and atomic numbers of all particles on either side of the arrow must be equal.
Learning Objective

Produce a balanced nuclear equation
Key Points

A balanced nuclear equation is one where the sum of the mass numbers (the top number in notation) and the sum of the atomic numbers balance on either side of an equation.

Nuclear equation problems will often be given such that one particle is missing.

Instead of using the full equations, in many situations a compact notation is used to describe nuclear reactions.
Term

baryon
A heavy subatomic particle created by the binding of quarks by gluons; a hadron containing three quarks. They have halfodd integral spin and are thus fermions.
Full Text
Nuclear reactions may be shown in a form similar to chemical equations, for which invariant mass, which is the mass not considering the mass defect, must balance for each side of the equation. The transformations of particles must follow certain conservation laws, such as conservation of charge and baryon number, which is the total atomic mass number. An example of this notation follows:
To balance the equation above for mass, charge, and mass number, the second nucleus on the right side must have atomic number 2 and mass number 4; it is therefore also helium4. The complete equation therefore reads:
Or, more simply:
Compact Notation of Radioactive Decay
Instead of using the full equations in the style above, in many situations a compact notation is used to describe nuclear reactions. This style is of the form A(b,c)D, which is equivalent to A + b gives c + D. Common light particles are often abbreviated in this shorthand, typically p for proton, n for neutron, d for deuteron, α representing an alpha particle or helium4, β for beta particle or electron, γ for gamma photon, etc. The reaction in our example above would be written as Li6(d,α)α.
Balancing a Radioactive Decay Equation
In balancing a nuclear equation, it is important to remember that the sum of all the mass numbers and atomic numbers, given on the upper left and lower left side of the element symbol, respectively, must be equal for both sides of the equation. In addition, problems will also often be given as word problems, so it is useful to know the various names of radioactively emitted particles.
Example
This could be written out as uranium235 gives thorium231 plus what? In order to solve, we find the difference between the atomic masses and atomic numbers in the reactant and product. The result is an atomic mass difference of 4 and an atomic number difference of 2. This fits the description of an alpha particle. Thus, we arrive at our answer:
Example
This could also be written out as polonium214, plus two alpha particles, plus two electrons, give what? In order to solve this equation, we simply add the mass numbers, 214 for polonium, plus 8 (two times four) for helium (two alpha particles), plus zero for the electrons, to give a mass number of 222. For the atomic number, we take 84 for polonium, add 4 (two times two) for helium, then subtract two (two times 1) for two electrons lost through beta emission, to give 86; this is the atomic number for radon (Rn). Therefore, the equation should read:
Key Term Reference
 alpha
 Appears in this related concepts: Description of the Hydrogen Atom, Halogen Compounds, and Disaccharides
 alpha particle
 Appears in this related concepts: The Rutherford Model, The Discovery of the Parts of the Atom, and Nuclear Reactors
 atomic mass
 Appears in this related concepts: The Noble Gases (Group 18), Early Ideas about Atoms, and MasstoMole Conversions
 atomic number
 Appears in this related concepts: The Incomplete Octet, The Periodic Table, and The Periodic Table
 beta particle
 Appears in this related concepts: Modes of Radioactive Decay and Indoor Pollution: Radon
 chemical equation
 Appears in this related concepts: ZeroOrder Reactions, MoletoMole Conversions, and Molecular, Ionic, and Complete Ionic Equations
 decay
 Appears in this related concepts: Radioactive Decay Series: Introduction, Models Using Differential Equations, and Sensory Registers
 electron
 Appears in this related concepts: Millikan's Oil Drop Experiment, Overview of Atomic Structure, and Microscopy
 element
 Appears in this related concepts: The Law of Definite Composition, Transuranium Elements, and Elements and Compounds
 emission
 Appears in this related concepts: Emission Spectrum of the Hydrogen Atom, New Energy Sources, and The Bohr Model
 mass defect
 mass number
 Appears in this related concepts: Average Atomic Mass, Atomic Number and Mass Number, and Isotopes
 neutron
 Appears in this related concepts: The Bottom of the Periodic Table, Nuclear Binding Energy and Mass Defect, and Substances and Mixtures
 nucleus
 Appears in this related concepts: Binding Energy and Nuclear Forces, The Shielding Effect and Effective Nuclear Charge, and Electric Charge in the Atom
 photon
 Appears in this related concepts: Electromagnetic Spectrum, Fluorescence and Phosphorescence, and Hydrogen Spectra
 product
 Appears in this related concepts: Promotional Strategies, Measuring Reaction Rates, and What is a Product?
 proton
 Appears in this related concepts: Atomic Radius, Weak Acids, and Development of the Periodic Table
 radioactive decay
 Appears in this related concepts: Alpha Decay, Nuclear Stability, and Tracers
 reactant
 Appears in this related concepts: The Law of Conservation of Mass, Writing Chemical Equations, and Chemical Reactions and Molecules
Sources
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Cite This Source
Source: Boundless. “Balancing Nuclear Equations.” Boundless Chemistry. Boundless, 25 Nov. 2014. Retrieved 20 May. 2015 from https://www.boundless.com/chemistry/textbooks/boundlesschemistrytextbook/nuclearchemistry19/nuclearreactions135/balancingnuclearequations539501/