chapter 25 – nuclear changes 25.1 - radioactivity
TRANSCRIPT
Chapter 25 – Nuclear Changes
25.1 - Radioactivity
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.
Nucleus•Composed of protons and
neutrons which account for most of the atom’s mass
Strong force•Causes protons and
neutrons to be attracted to each other in the nucleus
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
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
Isotopes•Atoms of the same element
with varying number of neutrons
•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
Symbol Atomic Number
Number of protons
Mass Number
Number of Neutrons
1H1
1 1 1 0
235U92
92 92 235 235-92 =
143
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
In-Class Assignment/Homework
• 25.1 Reinforcement WKT
• Tomorrow – – 25.1 Enrichment WKT– 25.1 & 25.2 Directed Reading WKT