Chapter 17: Properties of Atoms
Date:_____________
Section 3: Radioactivity - Notes
Learning Goals:
 Explain what radioactivity is.
 Describe the half-life of a radioactive element.
Protons and Neutrons:
 Protons and neutrons are packed tightly into the _______________________
of an atom.

Protons and neutrons are attracted to each other because of the
_________________________________.

Some atoms, such as ________________________, have many protons and neutrons in their nuclei.
o
These nuclei are held together __________________________________ than smaller atoms.
o
If the ____________________________ can keep all of the protons and neutrons together,
then the atom is ____________________.
Radioactivity:
 When the strong force is not strong enough to hold the nucleus together, the ____________________
can ______________________ and give off matter and _________________________.
o

This process is called __________________________________.
All nuclei that contain more than _____________________________________ are radioactive.
Nuclear Decay:
 When an unstable nucleus decays, particles and energy called _________________________________
__________________________ are emitted.
o

The three types of radiation are:

_____________________

_____________________

_____________________
When alpha radiation occurs, an ___________________________
________________________ is emitted.
o

An alpha particle is made of _____________ protons and _____________ neutrons
When an element gives off an alpha particle, it has two fewer protons… so it is a _________________
____________________________.

o
_________________________________: the process of changing one element into another
o
The new element will have two protons and two neutrons less than the original element.
Sometimes an unstable nucleus decays into a proton and emits an ____________________________.
o
The electron emitted is called a _______________________________________.
o
The atom now has one more _____________________ than the original atom and becomes a
new element.

Gamma rays are electromagnetic waves with the highest _________________________________ and
the shortest ____________________________ in the electromagnetic spectrum.
o
They have no ______________, no __________________, and travel at the speed of light
Radioactive Half-Life:
 Half-Life: the amount of time it takes for _______________ of the ____________________ in a sample
of radioactive isotopes to decay.

Half-lives vary widely among different radioactive elements.
o
Polonium-214 = less than ____________________________
o
Uranium-238 = ____________________________________
o
Carbon-14 = _______________________________________

___________________________ is often used to estimate the ages of plant and animal remains.

Carbon-14 is found in molecules such as _____________________________________

o
Which is used by plants to make _________________
o
When __________________________ eat plants, the carbon-14 is added to their bodies
The ratio of carbon-12 and carbon-14 in a plant or animal is ________________________________
___________________________ when the organism is alive.
o
When it dies, the carbon-14 atoms ____________________ and the ratio changes

By measuring this ratio, the ______________ of the organism’s remain can be
estimated.