Transcript Chemistry: Matter and Change

Section 24.1 Nuclear Radiation
• Summarize the events
that led to understanding
radiation.
• Identify alpha, beta, and
gamma radiations in
terms of composition
and key properties.
Section 24.1 Nuclear Radiation (cont.)
radioisotope
X ray
penetrating power
Under certain conditions, some nuclei
can emit alpha, beta, or gamma
radiation.
The Discovery of Radiation
• Nuclear reactions are different from other types of
reactions.
• Minerals that emit light after being exposed to
sunlight, a phenomenon called phosphorescence.
• Nuclear chemistry is concerned with the structure
of atomic nuclei and the changes they undergo.
• Marie Curie and her husband Pierre isolated the
first radioactive materials.
• Radioactivity : The process by which
materials give off spontaneous emissions
“rays” without exposed to the light.
The Discovery of Radiation (cont.)
Types of Radiation
• Isotopes are atoms of the same element that have
different numbers of neutrons.
• Isotopes of atoms with unstable nuclei are called
radioisotopes.
• Unstable nuclei emit radiation to attain more
stable atomic configurations in a process
called radioactive decay.
• The three most common types of radiation
are alpha, beta, and gamma.
Types of Radiation (cont.)
Types of Radiation (cont.)
• Alpha particles have the same composition as
a helium nucleus 24He—two protons and two
neutrons.
• Because of the protons, alpha particles have
a 2+ charge.
• Alpha radiation consists of a stream of
particles.
Types of Radiation (cont.)
• Alpha radiation is not very penetrating—a single
sheet of paper will stop an alpha particle.
• A radium-226 nucleus undergoes alpha decay to
form radon-222 and an alpha particle
What is the number of protons and neutrons
in radium-226 and radon-222?
Radium-226: 88 protons, 138 neutrons;
Radon-222: 86 protons, 136 neutrons
Types of Radiation (cont.)
• Beta particles are very fast-moving electrons
emitted when a neutron is converted to a
proton.
n→ p + β
• Beta particles have insignificant mass (almost
zero) and a 1– charge.
Types of Radiation (cont.)
• Beta radiation is a stream of fast moving
particles with greater penetrating power—a
thin sheet of foil will stop them.
• An iodine-131 nucleus undergoes beta decay
to form xenon-131 and a beta particle
• How does beta decay affect the mass
number of the decaying nucleus?
• The mass number does not change .
Types of Radiation (cont.)
• Gamma rays are high-energy electromagnetic
radiation.
• Gamma rays (short wavelength) are photons, which
are high-energy
• Gamma rays have no mass or charge so the emission
of gamma rays does not change the atomic number or
mass number of a nucleus.
• Gamma rays almost always accompany alpha and
beta radiation.
• X rays are a form of high-energy electromagnetic
radiation emitted from certain materials in an excited
state.
Q: Compare and contrast X-rays and gamma
rays.
X-rays are emitted from materials that are in
an excited state. Gamma rays are produced
by radioactive sources.
Types of Radiation (cont.)
• The ability of radiation to pass through
matter is called its penetrating power.
• Gamma rays are highly penetrating because
they have no charge and no mass.
Section 24.1 Assessment
Why do radioisotopes emit radiation?
A. to balance charges in the nucleus
B. to release energy
C. to attain more stable atomic
configurations
D. to gain energy
A.
B.
C.
D.
A
B
C
D
Section 24.1 Assessment
X rays are most similar to what type of
nuclear emissions?
A. gamma rays
B. alpha particles
C. beta particles
D. delta waves
A.
B.
C.
D.
A
B
C
D
• Q1: List the different types of radiation and
their charges.
• alpha (2+), beta (1-), and gamma (0)
• Q2: Compare the subatomic particles
involved in nuclear and chemical reactions.
• Protons, electrons, and neutrons can be
involved in nuclear change; only electrons
are involved in chemical change.
• Q3: Explain how you know whether the
reaction is chemical or nuclear when an
atom undergoes a reaction and attains a
more-stable form.
• If the new, more stable form of the atom
has an identity different from the original
atom, a nuclear process has occurred.
Which statement is NOT true of beta
particles?
A. They have the same mass as an electron.
B. They have a charge of 1+.
C. They are less penetrating
than alpha particles.
D. They are represented by 0-1β.
A.
B.
C.
D.
A
B
C
D
End of section 24.1