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U N I T
L E C T U R E
1
N O T E S
LECTURE 15
Nuclear Processes
(19.1, 19.2, & 19.3)
GENERAL CHEMISTRY
Fall 2009
Updated: 6/28/2017
I. Introduction
A. History
1. Wilhelm Conrad Roentgen (1895)
Discovered x-rays
2. Antoine Henri Becquerel (1896)
Uranium emissions were continuous and required no
energy from an external source.
3. Marie and Pierre Curie (1898)
a. Isolated two new elements, radium and polonium
b. Marie Curie is the only scientist to win Nobel Prizes
from two different sciences (1903 – physics; 1911 –
chemistry)
4. Ernest Rutherford (1911)
a. Radioactive elements undergo a process of decay over
time
b. First to artificially transmute one element into another
B. Nuclear reactions
1. Involve great quantities of energy
Strong nuclear force overcomes electrostatic repulsion between
protons
2. Differ from chemical reactions
a. atomic numbers change
b. some matter is changed to energy
c. specific isotopes involved
C. Nucleons
1. Neutrons and protons
D. Nuclides
1. Atoms identified by the number of protons and neutrons in
the nucleus
II. Radioactivity
A. Radioisotopes
1. Isotopes of atoms with unstable nuclei
B. Radioactive Decay
1. The spontaneous disintegration of a nucleus into a slightly
lighter and more stable nucleus, accompanied by emission of
particles, electromagnetic radiation, or both
2. Decay of each nucleus is called an event
C. Nuclear Radiation
1. Particles or electromagnetic radiation emitted from the
nucleus during radioactive decay
D. Unstable Nuclides
1. All nuclides beyond atomic # 83 are unstable and
radioactive
Updated: 6/28/2017
19.1 Radioactive decay
III. Three Types of Radioactive Decay
A.
Alpha Emission
1. Alpha particle () is a helium nucleus ( 42 He), so it has an
atomic number of 2 and atomic weight of 4 amu.
2. Alpha emission is restricted almost entirely to very heavy
nuclei
3. High energy, relatively low velocity
4. Stopped by a thickness of a sheet of paper; skin
5. Example
230
226
4
90 Th  2 He + 88 Ra
B.
Beta Emission
1. Beta particle () is an electron emitted from the nucleus
during nuclear decay
2. Beta particles are emitted when a neutron decays into a
proton and an electron
3. High velocity; low energy
4. Stopped by 1 cm of Al or thickness of average textbook
5. Example
234
234
0
91 Pa  92 U + 1 e
C.
Gamma Emission
1. Gamma rays () are high-energy electromagnetic waves
emitted from a nucleus as it changes from an excited state to a
ground energy state
2. Gamma rays are produced when nuclear particles undergo
transitions in energy levels; beta and gamma rays are usually
emitted together
3. Gamma emission usually follows other types of decay that
leave the nucleus in an excited state
4. Requires about 13 cm of lead to shield from gamma rays
Symbol
Name



Alpha
Beta
Gamma
Mass
number
4
0
0
Charge Identity
+2
-1
0
Helium nucleus
High-energy electron
High-energy particle of light
Updated: 6/28/2017
19.2 Nuclear Transformations
Nuclear transformation is defined as the change of one element into another.
Elements above 93 (transuraniums) have been synthesized by
bombardment.
19.3 Detection of radioactivity and half-life
IV. Methods of detecting rays
A. Photographic plate
a. Film badges use exposure of film to measure radiation exposure
of people working with radioactive materials
B. Scintillation counter
a. Small flashes of light are observed on fluorescent screen (ZnS)
C. Geiger counter
a. Most widely used instrument
V. Half-Life
A. Half-Life (t1/2)
1. The time required for half the atoms of a radioactive nuclide
to decay
a. More stable nuclides decay slowly
b. Less stable nuclides decay rapidly
2. Amount remaining = (Initial amount) (1/2) n, where n is
equal to the number of half-lives that have passed.
3. Examples
Sample A has a mass of 1.00g and a half-life of 30 days.
How much of the sample is left after 90 days?
Updated: 6/28/2017