The
International School of Panama
General
Chemistry
Unstable
Nuclei and Radioactive Decay
Radioactivity
Radioactivity
was
discovered by accident by Antoine Henri Becquerel.
http://www.accessexcellence.org/AE/AEC/CC/historical_background.html#becquerel
Radioactivity: The process in which some substances spontaneously emit radiation.
Nuclear Reaction: A reaction that involves changes in an atom’s nucleus.
|
Chemical
Reactions |
Nuclear
Reactions |
|
The
atoms of one or more substances are rearranged. |
The
nuclei of atoms change. |
|
Only
the electrons are given, accepted or shared during chemical
reactions. Te particles in the nuclei remain the same. |
The
number of protons and neutrons change during nuclear reactions. |
|
The
identity of the atoms do not change |
The
identity of the atoms change: atoms of different elements are
formed. |
The
rays and particle emitted by radioactive materials are called radiation.
Why
do some atoms emit radiation?
Because
their nuclei are unstable.
They
gain stability by losing energy. They lose energy by emitting radiation
in a spontaneous process called radioactive decay.
Why
are some nuclei unstable?
Because
they have too many or too few neutrons compared to the amount of protons.
Therefore the primary factor in the stability of a nucleus is its ratio of
neutrons to protons.
Types
of radiation
http://cwx.prenhall.com/bookbind/pubbooks/blb/chapter2/medialib/blb0202.html
Tyes
of radiation
Deviated towards the negatively charged plate:
Alpha
radiation, Made up of alpha particles.
Deviated
towards the positively charged plate:
Beta
radiation,
Made up of beta particles.
Not
deflected by electric of magnetic fields:
Gamma
radiation, not
made of particles.
Characteristics
of alpha, beta and gamma radiat
|
Radiation |
Symbol |
Mass
(amu) |
Charge |
|
Alpha |
42
He or 42
a
|
4 |
2+ |
|
Beta |
0-1b |
1/1837 |
1- |
|
Gamma |
00
g |
0 |
0 |
We
can express a radioactive decay as a nuclear equation. This type of
equation shows the atomic number and mass number of the atoms involved. When
balancing or completing nuclear reactions remember that both, atomic number
and mass number are conserved.
Gamma
rays
usually accompany alpha and beta decays. They are the most energetic of the
three types of radiation, the most penetrating and the ones that cause more
damage.
Example
1:
Write the alpha decay of Radium-226. What element is formed?
22688Ra ---à
??X
+ 42 He
+ 00 g
226 – 4 = 222
88 – 2 = 86 (look for this atomic number in the PT)
The
element formed is Radon-222
22688Ra ---à
22286Rn
+ 42 He
+ 00
g
Example
2:
Write the beta decay of Carbon-14. What element is formed?
146C ---à
??X
+ 0-1 b
+ 00 g
6 – (-1) = 7 (look for this atomic number in the PT)
The
element formed is Nitrogen-14
146C ---à
147N
+ 0-1 b
+ 00 g
Example
3:
Write the alpha decay of Uranium-238. What element is formed?
23892U
---à
??X
+ 42 He
+ 00 g
238
– 4 = 234
92 – 2 = 90 (look for this atomic number in the PT)
The
element formed is Thorium-234
23892U
---à
23490Th
+ 42 He
+ 00 g
