Learning Targets
• I can name the force that holds the atom’s
nucleus together
• I can describe the two reasons why some
isotopes are radioactive.
• I can describe the four types of radiation
• I can predict the type of decay an element
will go through to become stable.
Nuclear Reactions
• Nuclear Reactions involve the nucleus and may
change one element into another
• Two types:
– Decay reactions- nucleus
spontaneously breaks up
– Bombardment reactions- a nucleus is struck by
another nucleus or some nuclear particle, such as a
neutron or proton
• Radiation- transmission of energy through space
– Nuclear reactions involve much more energy than
chemical reactions.
Radioactive Elements
• Elements with an unstable nucleus will spontaneously lose particles
or energy to become stable. Two reasons for instability:
– Nucleus is too large (atomic # > 83)
•
The nucleus is held together with
the STRONG FORCE, which at short
distances is stronger than the
electromagnetic force that would
cause protons to repel
• At longer distances (larger nucleus)
the electromagnetic force takes over
and the nucleus begins to fall apart.
– Imbalance between protons and neutrons
• In smaller elements a 1:1 ratio is stable
• In larger elements more neutrons are required to hold the
nucleus together
Radioactive Isotopes
• All elements with an atomic
number over 83 are radioactive
• Many other smaller elements have
radioactive isotopes. (Carbon-14)
• In graph (at right), dotted line
shows the “Belt of Stability”.
A:
B:
C:
Types of Radioactive Decay
• Alpha radiation
– A helium nucleus
(2 protons and 2
neutrons) are
ejected
The nucleus changes! The atomic
number is decreased by 2!
• Beta radiation
– A neutron becomes
a proton, and an
electron is ejected
The atomic number increases by 1!
Types of Radiation
• Positron emission
– a proton is converted
to a neutron and
a positron (e+) is
emitted
• Gamma radiation
– The nucleus
does not change,
but energy is
released
Learning Check
• What is the name of the force that holds protons together
in the nucleus?
• What are the two reasons that an element could be
radioactive?
• What happens to the nucleus during
–
–
–
–
alpha decay?
beta decay?
positron emission?
gamma decay?
• Predict the type of decay for each element:
– Uranium- 235
– Lithium-8
– Oxygen-15