Radioactivity

Chapter 25: 1-3 Homework

• Reading Preparation
• WebLecture
• Study Activity
• Preparation work for chat
• Online Quiz
• Lab Instructions

Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 25: 1-3.

Study Notes

• 25.1 The balance of forces within the nucleus are determined by the ratio of neutrons to protons. In stable atoms, this balance preserves the nucleus intact for long periods of time; in unstable atoms, the forces push nuclear components out to reach a more stable energy level. This "decay" of the nucleus can take the form of
  • α (alpha) radiation: the ejection of a 2-proton, 2-neutron particle. Alpha emission decreases both the proton and neutron count, and in most cases increases the neutron-to-proton ratio.
  • β (beta) radiation: the ejection or capture of either an electron or a positron. Normal beta emission (electron ejection) increases the atomic number and decreases the neutron-to-proton ratio.
  • γ (gamma) radiation: the ejection of energy in the form of a photon
• 25.2 Nuclear reaction equations resemble chemical reaction equations in that all particles and charges must be accounted for. The total number of nucleons cannot change, and the total amount of charge cannot change.

  A decay reaction may not result in a stable nucleus; subsequent decay reactions may occur in a predictable series (based on observational evidence).

• 25.3 If we take into account all the isotopes of all elements, very few isotopes are actually stable. All isotopes beyond ¹²⁶₈₃Bi are unstable. Most stable isotopes have either an even number of protons, an even number of neutrons, or an even number of both.

  The mass of a nucleus is less than the sum of the masses of its components. We account for the missing mass or mass defect by assuming that it has been converted to the energy used to bind the components together: E_binding = Δmc².

Read the following weblecture before chat: Radioactivity

Study Activity

Chat Preparation Activities

• Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

Chapter Quiz

• Required: Complete the Mastery exercise with a passing score of 85% or better.
• Go to the Moodle and take the quiz for this chapter.

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There is no lab for this chapter.

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