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Balancing Nuclear Equations & Predicting the Product of a Nuclear Reaction

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  • 0:08 Nuclear Equations
  • 1:01 Alpha Decay
  • 3:04 Beta Decay
  • 5:27 Gamma Decay
  • 6:55 Lesson Summary
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Lesson Transcript
Instructor: Kristin Born

Kristin has an M.S. in Chemistry and has taught many at many levels, including introductory and AP Chemistry.

When a radioactive particle gives off radiation, what happens to the particle? This lesson will explain the three major types of radiation and what effect they have on the decaying atom.

Balancing Nuclear Equations

The more you learn about chemistry, the more you will see that it really is a study of change and the way things undergo change. Atoms and molecules commonly undergo change when they are unstable: a match burns to create a more stable product, atoms lose or gain electrons to become more stable, and the nucleus of an atom will emit nuclear radiation to become more stable.

The key to all of these events is they always lead to products that are more stable than their ingredients, or as chemists like to call them, reactants. One way chemists represent change is by using an arrow. The reactants are shown on the left, and the products are shown on the right. In this lesson, we are going to learn to write nuclear equations to symbolize the changes that take place in the nucleus during a nuclear reaction.

Alpha Decay

I want to start by asking you this: have you ever wanted to go on a diet? What is the reason people go on diets? Usually, it is because they have some level of unhappiness in their current state and they figure if they lose a few pounds, they'll be happier. Atoms sometimes feel the same way. When an atom's nucleus gets too massive - it has too many protons and neutrons - it decides to go on a diet. The heaviness of its nucleus is making it unstable, and if it sheds a little weight, it will become more stable. To do this, it will undergo alpha decay.

For example, let's start with an atom of americium-241, the isotope that is in your smoke detector. Using nuclear symbols, we would write it like this:

Nuclear symbol of americium-241
am 241 symbol

This isotope is very unstable (or unhappy) because it is too heavy. It wants to slim down a bit, so it is going to undergo alpha decay, losing an alpha particle.

So, we would write the equation like this: americium-241 first, then an arrow (-->), which represents that a change is going to take place. On the right of the arrow, we would write the symbol for an alpha particle because it is one of the products of our reaction.

Now, we just need to find out what remains after the alpha particle is lost. To do this, we are going to use the numbers in the nuclear symbol and treat the arrow as if it was an equal sign. On the top, we would have 241 equals 4 + 'something'. Using a little algebra, we know that the number 'something' has to be 237, which will be the mass number of our newer, lighter, happier particle. On the bottom, we have 95 (the atomic number of americium) equals 2 (the atomic number of the alpha particle) + something. That 'something' is going to be a 93. So, our new product is neptunium which is the element with an atomic number of 93. That's how alpha decay works!

The new product neptunium is created after alpha decay occurs.
Alpha Decay Equation Example

Beta Decay

Now, have you ever had a big dinner and had so many leftovers that you used some of your skills in the kitchen to turn them into another meal? I undoubtedly do this every year after Thanksgiving: the big turkey dinner on one day turns into some sort of turkey and potato soup the next day. This is exactly what potassium-40 does.

Potassium-40 is found in bananas, and it has so many neutrons compared to its number of protons that it turns a neutron into a proton! The nucleus of the atom is super unstable (or unhappy) and to make it more stable, it needs to undergo beta decay.

In this process, a high-energy electron (or beta particle) is released. Just like our recreation of Thanksgiving dinner, the mass of the atom stays the same; however, the atomic number changes because the product will have one extra proton. And, because the atomic number determines the identity of the element, the type of element will also change. Potassium-40 that undergoes a beta decay will turn into calcium-40, a metal with the same weight but slightly different properties than those of potassium.

This equation shows the result of beta decay on potassium-40.
Beta Decay Equation Example

Let's try another example of beta decay. Say you have some strontium-90, a common material used in the treatment of cancer. We will first start out by writing the nuclear symbol for strontium-90, then an arrow indicating that a change will take place. On the right of the arrow, we will have our symbol for the beta particle, followed by the atom that remains after the decay is complete.

To find out which atom this is, we need to use the equation: 90 (the mass number of this isotope) equals 0 (the mass number of a beta particle) + 'something'. Hopefully, you are easily able to see that 90 = 0 + 90, so our new particle will have a mass number of 90 (as we predicted, because during beta decay the mass does not change). On the bottom, we have 38 (the atomic number of strontium) equals -1 + something. Using a little algebra, we are able to see that 38 = -1 + 39. So, our new, more stable, much happier element is yttrium-90.

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