Transcript Radioactivity is the spontaneous emission of

Radioactive Decay
Radioactivity-Chapter 21
• Radioactivity is the spontaneous
emission of radiation from an atom
• Why are there neutrons in the nucleus?
• Protons in the nucleus repel each
other.
• Neutrons are a stabilizing force.
• think of neutrons as the glue that holds
the nucleus together
UNSTABLE NUCLEI
• nuclei are unstable if they contain too few
or too many neutrons
• nuclei that have excess neutrons are likely
to emit beta radiation
• Generally, isotopes that are much
heavier (contain more neutrons) or
much lighter (contain fewer neutrons)
than the most common isotope are
likely to be radioactive.
STABLE OR NOT?
• elements with:
• atomic number 1-20: stable nuclei have almost
equal numbers of protons and neutrons
• atomic number 21-83: nuclei need more
neutrons than protons to be stable
• atomic number >83: no number of neutrons is
sufficient to hold the nucleus together
indefinitely.
• All nuclei with atomic numbers greater than 83
are radioactive.
Types of Decay
• Alpha
• Beta
• Gamma
Notes/Examples
• http://ithacasciencezone.com/chemzone/le
ssons/11nuclear/nuclear.htm
• http://www.chem.ox.ac.uk/vrchemistry/Con
servation/page30.htm
• Go on-line and take a look at these
web-sites.
Practice Decay Problems