chapter 25 – nuclear changes 25.1 - radioactivity
TRANSCRIPT
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Chapter 25 – Nuclear Changes
25.1 - Radioactivity
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Objectives
• Describe the structure of an atom and its nucleus.
• Explain what radioactivity is.• Compare and contrast properties of
radioactive and stable nuclei.• Discuss the discovery of radioactivity.
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Nucleus•Composed of protons and
neutrons which account for most of the atom’s mass
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Strong force•Causes protons and
neutrons to be attracted to each other in the nucleus
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Video clip
• The strong force is powerful only when neutrons and protons are close to each other
• The protons and neutrons in a large nucleus are held less tightly by the strong force than those in a small nucleus
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Radioactivity
•The nuclear decay that occurs when the strong force is not large enough to hold the nucleus together and the nucleus gives off matter and energy
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Isotopes•Atoms of the same element
with varying number of neutrons
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•A nucleus with too many or too few neutrons compared to protons is radioactive–Atomic number = number of protons in an atom
–Mass number = number of protons and neutrons in a nucleus
– If an element has a neutron to proton ratio of 1.2 or higher than the element is radioactive
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Symbol Atomic Number
Number of protons
Mass Number
Number of Neutrons
1H1
1 1 1 0
235U92
92 92 235 235-92 =
143
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Element Radioactivity•Uranium was discovered in
1896 by Henri Becquerel as a radioactive element
•Polonium and Radium were discovered as radioactivity by Marie and Pierre Curie in 1898Video Clip
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In-Class Assignment/Homework
• 25.1 Reinforcement WKT
• Tomorrow – – 25.1 Enrichment WKT– 25.1 & 25.2 Directed Reading WKT