Download Radioactive Decay

Ch. 21
Nuclear
Chemistry
The Nucleus

__________: Protons and neutrons.
__________: 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: ________________, or as follows:
Atomic mass =
35
Atomic number = 17
Cl
21-2
The Nucleus
________________: the difference between the mass of an atom
and the sum of the masses of its protons, neutrons and electrons.

__________________: the energy released when a nucleus is
formed from nucleons.

___________________: nucleons exist in different energy
levels, or shells, in the nucleus. The numbers of nucleons that
represent completed nuclear energy levels ~ 2, 8, 20, 28, 50, 82
and 126 are called Magic Numbers.

21-3
Radioactive Decay
_______________: a reaction that changes the nucleus of an
atom.
________________: a change in the identity of a nucleus as a
result of a change in the number of its protons.
Nuclear Particles

Type
Alpha particle
Beta particle
Positron
Neutron
Gamma Ray
Symbol
4 He
2
0 β
-1
0 β
+1
1 n
0
γ
Charge
+2
-1
+1
0
0
21-4
Mass(amu)
4.0015062
0.0005486
0.0005486
0
Radioactive Decay
21-5
Radioactive Decay
___________________: the spontaneous disintegration of a
nucleus into a slightly lighter nucleus, accompanied by emission of
particles, electromagnetic radiation or both.

_____________________: particles or electromagnetic radiation
emitted from the nucleus during radioactive decay.

____________________: an unstable nucleus that undergoes
radioactive decay.

21-6
Radioactive Decay
_______________ (α): two protons and two neutrons
bound together, emitted during some types of radioactive
decay.

21-7
Radioactive Decay
___________________ (β): an electron emitted from
the nucleus during some types of radioactive decay.

21-8
Radioactive Decay
______________ : 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
______________ (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
Po → 42He + 20882 Pb
1) Balance the following reaction:
253 Es + 4 He → 1 n + ________
99
2
0
212
253
84
99
Es + 42He → 10n + 256101 Md
21-10
Radioactive Decay
____________ : the time required for half the atoms
of a radioactive nuclide to decay.

21-10
Radioactive Decay
Example: Phosphorous-32 has a half-life of _______, how many
milligrams of P-32 remain after ______________ if you start with a
__________ sample?
# of half-lives = time elapsed x 1 half-life = 57.2 days x 1 half-life
14.3 days
14.3 days
= _____________
Amount of P-32 = original amount x # of half-lives
= 4.0 mg x ½ x ½ x ½ x ½ = ____________
21-12
Radioactive Decay
2) Polonium-210 has a half-life of 138.4 days, how many
milligrams of Po-210 remain after 415.2 days if you start
with a 2.0 mg sample?
21-13
Radioactive Decay
Example: Assuming a half-life of _________, how many
years will be needed for the decay of ________ of a given
amount of radium-226?
Amount remaining = 1/16 = 0.0625 = (½)4 = ____________
Years needed for decay of 15/16 = (1599 years) (__) = ___________
21-14
Radioactive Decay
3) The half-life of radon-222 is 3.824 days, after what time
will one-fourth of a given amount of radon remain?
21-15
Radioactive Decay
___________: a series of radioactive nuclide produced by
successive radioactive decay until a stable nuclide is reached.

21-15
Radioactive Decay
______________: a very heavy nucleus splits into more stable
nuclei of intermediate mass, starting a chain rxn.

21-17
Radioactive Decay
_____________: low mass nuclei combine to form a heavier,
more stable nucleus.

21-18
Ch. 21
The
End!