Download Radioactive Decay

Ch. 21
Nuclear
Chemistry
The Nucleus

Nucleons: Protons and neutrons.
Nuclide: an atom, identified by the number of
protons and neutrons in its nucleus.

Nuclides can be written with the name or symbol,
followed by a dash with the mass number:
Chlorine-35 or Cl-35, or as follows:
Atomic mass =
35
Atomic number = 17
Cl
21-2
The Nucleus
Mass Defect: the difference between the mass
of an atom and the sum of the masses of its
protons, neutrons and electrons.

Nuclear Binding Energy: the energy released
when a nucleus is formed from nucleons.

Nuclear Shell Model: nucleons exist in
different energy levels, or shells, in the nucleus.

21-3
Radioactive Decay
Nuclear Reaction: a reaction that changes the nucleus
of an atom.
 Transmutation: a change in the identity of a nucleus as
a result of a change in the number of its protons.
Nuclear Particles
Type
Symbol
Charge

Alpha particle
Beta particle
Positron
Neutron
Gamma Ray
4
2He
-1β
0
+1β
0
1
0n
γ
+2
-1
+1
0
0
Radioactive Decay
21-5
Radioactive Decay
Radioactive Decay: the spontaneous
disintegration of a nucleus into a slightly lighter
nucleus, accompanied by emission of particles,
electromagnetic radiation or both.

Nuclear Radiation: particles or electromagnetic
radiation emitted from the nucleus during
radioactive decay.

Radioactive Nuclide: an unstable nucleus that
undergoes radioactive decay.

21-6
Radioactive Decay
Alpha emission (α): two protons and two
neutrons bound together, emitted during some
types of radioactive decay.

21-7
Radioactive Decay
Beta emission (β): an electron emitted from the
nucleus during some types of radioactive decay.

21-8
Radioactive Decay
Positron emission : a particle that has the same
mass as an electron, but has a positive charge and
is emitted during some types of radioactive
decay.

21-9
Radioactive Decay
Gamma Rays (γ): high energy electromagnetic waves
emitted from a nucleus as it changes from an excited
state to a ground state.
Example: Balance the following reaction:
212 Po → 4 He + ________
84
2

4 He + 208 Pb
Po
→
84
2
82
1) Balance the following reaction:
253 Es + 4 He → 1 n + ________
99
2
0
212
4 He → 1 n + 256
Es
+
99
2
0
101 Md
253
Radioactive Decay
Half-Life : the time required for
half the atoms of a radioactive
nuclide to decay.

21-11
Radioactive Decay
Decay Series: a series of radioactive nuclide produced by
successive radioactive decay until a stable nuclide is reached.

21-15
Radioactive Decay
Nuclear Fission: a very heavy nucleus splits into more stable
nuclei of intermediate mass, starting a chain rxn.

21-13
Radioactive Decay
Nuclear Fusion: low mass nuclei combine to form a heavier, more
stable nucleus.

21-14
Ch. 21
The
End!