• March 7th, 2016

Geology (and other Earth Sciences)

Paper, Order, or Assignment Requirements

Vocabulary: alpha particle, atomic number, beta particle, daughter product, gamma ray, isotope, mass number, nuclear decay, positron, radioactive, subatomic particle

 

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

The chart below gives the locations, charges, and approximate masses of three subatomic particles. The approximate mass of each particle is given in universal mass units (u).

 

Particle Location Charge Approximate mass
Proton Nucleus 1+ 1 u
Neutron Nucleus 0 1 u
Electron Orbitals 1 0 u

 

  1. The mass number of an atom is equal to the sum of protons and neutrons in the nucleus.
    A helium atom has 2 protons and 2 neutrons. What is the mass number of this atom? _____

 

  1. The atomic number of an element is equal to the number of protons in each atom of the element. All helium atoms have 2 protons. What is the atomic number of helium?

 

Gizmo Warm-up

While most atoms are stable, some are radioactive, which means that they have a tendency to undergo spontaneous nuclear decay. The decay of radioactive atoms generally results in the emission of particles and/or energy.

 

Several types of nuclear decay can be explored with the Nuclear Decay Gizmo™. On the Gizmo, check that Alpha decay and Uranium are selected.

 

  1. Click Play ( ) and then click Pause ( ) when the alpha particle is clearly visible. What is an alpha particle made of?

 

  1. Click Play and observe. Besides the alpha particle, what else is emitted from the nucleus during alpha decay?

 

Gamma rays are energetic electromagnetic waves; they are often emitted in nuclear decay.

Activity A:

 

Alpha decay

Get the Gizmo ready:

·      Click Reset ( ).

·      Check that Alpha decay and Uranium are selected.

 

Question: How does alpha decay change the nucleus of a radioactive atom?

 

  1. Predict: As you observed in the warm-up activity, an alpha particle consists of two protons and two neutrons. How will the emission of an alpha particle affect the following?

 

  1. The atomic number of the atom:

 

  1. The mass number of the atom:

 

  1. Calculate: Turn on Write equation. What you see is an equation that shows the original uranium atom on the left. The boxes on the right represent the daughter product—the atom produced by radioactive decay—and the emitted alpha particle.

 

  1. In the top left box, write the mass number of the daughter product and press “Enter” on your keyboard. What is this number?
  2. In the bottom left box, write the atomic number of the daughter product and press “Enter.” What is this number?
  3. In the next set of boxes, enter the mass number and atomic number of the alpha particle, which has the same composition as the nucleus of a helium (He) atom. After filling in the boxes in the Gizmo, write the completed equation below:

 

     

+

   
   
238U

92

New mass number
New atomic number

 

  1. According to your equation, what isotope remains after the alpha decay of
    uranium-238? (Note: You can look up element symbols on the periodic table.)
  1. Check: Turn on Show equation, and click Play. The equation will appear at the end of the animation. Was your prediction correct? If not, modify your equation above.

 

 

  1. Practice: Click Reset, turn off Show equation, and select Polonium. Write an equation for the alpha decay of polonium, and then use the Gizmo to check your answer.

 

     

+

   
   
212Po

84

New mass number
New atomic number

 

What isotope remains after the alpha decay of polonium-212?

  1. Practice: Click Reset, turn off Show equation, and select Radium. Write an equation for the alpha decay of radium, and then use the Gizmo to check your answer.

 

     

+

   
   
226Ra

88

New mass number
New atomic number

 

 

What dangerous gas is produced by the decay of radium-226?

 

  1. Practice: Americium-241 is a radioactive isotope used in smoke detectors. Write an equation for the alpha decay of Americium-241 below.

 

     

+

   
   
241Am

95

New mass number
New atomic number

 

  1. Analyze: In each equation, how is the mass number on the left side of the arrow related to the sum of mass numbers on the right side of the arrow? Is this true for atomic numbers?

 

  1. Summarize: In general, how can you determine the mass number of the daughter product after alpha decay has taken place? How can you determine the atomic number?
  1. Think and discuss: Helium is the second most abundant element in the universe, but it is rare in Earth’s atmosphere. Most of the helium used to fill balloons and blimps must be extracted from Earth’s crust. How do you think this helium formed?

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