Matter can undergo physical, chemical, and nuclear changes, with nuclear changes involving transformations of an atom's nucleus. Radioactivity is the spontaneous emission of nuclear radiation from unstable isotopes, resulting in their decay until stable isotopes are formed, accompanied by significant energy release. There are three main types of nuclear radiation: alpha particles, beta particles, and gamma rays, each with distinct properties and levels of penetration.

1. Changes in Matter
• Matter can undergo three types of changes.
– Physical Change – change in appearance but not
identity.
– Chemical Change – production of new substances
with different properties – same elements just
rearranged – usually involves valence electrons.
– Nuclear Change – form different element from what
you started.
• Nuclear changes involve changes in
the nucleus of an atom.

2. Radioactivity
• Radioactivity – spontaneous emission of rays or
particles from certain elements. (like uranium)
– also known as radioactive decay
– rays and particles emitted from a radioactive source are
called nuclear radiation
• Radioactivity is an example of a nuclear reaction.
– Purpose of radioactive decay is for an unstable nucleus to
become stable.
– Nuclear reactions begin with unstable isotopes
known as radioisotopes.
– Atoms become stable when changes occur
in the nuclei.

3. – These changes are always accompanied by the
emission of large amounts of energy.
– Unlike chemical reactions, nuclear reactions are
not affected by changes in temperature, pressure,
or the presence of catalysts.
– Nuclear reactions of given radioisotope cannot be
slowed down, speeded up, or stopped.
– Radioactive decay is a spontaneous process.
– If the product of a nuclear reaction is unstable, it
will decay again.

4. – The process continues until unstable isotopes of one
element are changed, or transformed, into stable
isotopes of a different element.
– These stable isotopes are not radioactive.
– Nuclear radiation is emitted during radioactive decay.
– There are three main types of nuclear radiation:
alpha radiation, beta radiation, and gamma radiation.

5. Types of Radiation
Alpha Radiation
– An alpha particle (α) is two protons and two
neutrons bound together and is emitted from the
nucleus during some kinds of radioactive decay.
(also referred to a as a helium nucleus)
– Alpha particles have a positive charge
– In nuclear equations, an alpha particle is written as
– Example:

6. • When an atom loses an alpha particle, the atomic
number of the product is lowered by two and the
mass number decreases by four.
• In balanced nuclear equations, the sum of the mass
numbers on the right must equal the sum on the left.
• This is also true for the atomic numbers.
• Alpha particles are the least penetrating type of
radiation .
– Sheet of paper or the surface of your skin can stop them.

7. Beta Radiation
– A beta particle (β) is an electron emitted from the
nucleus during some kinds of radioactive decay.
– A beta particle is formed when a neutron breaks
apart into a proton and an electron.
– The proton remains in the nucleus while the electron
is ejected.
– The -1 refers to the charge of the electron and the 0
refers to the mass. (essentially zero)

8. – Example:
• When an atom loses a beta particle, the atomic
number of the product is increased by one; however,
the mass number remains the same.
• Since a beta particle has less charge and much less
mass than an alpha particle, beta particles are more
penetrating than alpha particles.
– Beta particles can pass through paper but are stopped
by aluminum foil or thin pieces of wood.

9. Gamma Radiation
– Gamma rays (γ) are high-energy waves emitted
from a nucleus as it decays.
– Gamma rays have no mass and no electrical
charge. Therefore, gamma radiation does not
alter the atomic number or mass number of an
atom.
– Nuclei often emit gamma rays along with alpha or
beta particles.

10. • Gamma rays are the most penetrating type of
nuclear radiation.
• Easily pass through paper, wood, and human body
(extremely dangerous).
• They can be stopped, although not completely, by
several meters of concrete or several centimeters of
lead.

11. Nuclear Equations and Radioactive Decay
• Radium-226 is a radioactive isotope that decays by
releasing an alpha particle. Write a nuclear equation
for the radioactive decay of radium-226.
• Potassium-40 decays by releasing a beta particle.
Write a nuclear equation that represents the
radioactive decay of potassium-40.

12. Balancing Nuclear Equations

13. Nuclear Equations Sample Problem
1. Identify the product that balances the following
nuclear reaction:

14. Reflection
• Fill in the following table on your page.