SECTION 3:
RADIOACTIVITY
Chapter 17: Properties of Atoms
WARM-UP:
What
do you think it means to be
radioactive?
 What is one element or thing that you
know of that is radioactive?
LEARNING GOALS
Explain
what radioactivity is.
Describe
element.
the half-life of a radioactive
PROTONS AND NEUTRONS
Protons
and neutrons are packed
tightly into the nucleus of an atom.
 Protons and neutrons are attracted to
each other because of the strong force.
PROTONS AND NEUTRONS
Some
atoms, such as uranium (U),
have many protons and neutrons in
their nuclei.
 These nuclei are held together less
tightly than smaller atoms.
 If the strong force can keep all of the
protons and neutrons together, then
the atom is stable.
RADIOACTIVITY
When
the strong force is not strong
enough to hold the nucleus together,
the nucleus can decay and give off
matter and energy.
 This process is called radioactivity.
All
nuclei that contain more than 83
protons are radioactive.
NUCLEAR DECAY
When
an unstable nucleus decays,
particles and energy called nuclear
radiation are emitted.
 The three types of radiation are:

Alpha

Beta

Gamma
NUCLEAR DECAY
When
alpha radiation
occurs, an alpha
particle is emitted.
 An alpha particle is
made of two protons
and two neutrons
NUCLEAR DECAY
When
an element gives off an alpha
particle, it has two fewer protons…
so it is a different element.
 Transmutation: the process of changing
one element into another
 The new element will have two protons
and two neutrons less than the original
element.
NUCLEAR DECAY
Sometimes
an unstable nucleus
decays into a proton and emits an
electron.
 The electron emitted is called a beta
particle.
 The atom now has one more proton
than the original atom and becomes a
new element.
NUCLEAR DECAY
Gamma
rays are electromagnetic
waves with the highest frequencies
and the shortest wavelengths in the
electromagnetic spectrum.
 They have no mass, no charge, and
travel at the speed of light
RADIOACTIVE HALF-LIFE
Half-Life:
the amount of time it takes
for half of the nuclei in a sample of
radioactive isotopes to decay.
RADIOACTIVE HALF-LIFE
Half-lives
vary widely among
different radioactive elements.
 Polonium-214 = less than 0.001 sec
 Uranium-238 = 4.5 billion years
 Carbon-14 = 5,730 years
RADIOACTIVE HALF-LIFE
Carbon-14
is often used to estimate
the ages of plant and animal remains.
Carbon-14
is found in molecules such
as carbon dioxide
 Which is used by plants to make sugar
 When animals eat plants, the carbon-14
is added to their bodies
RADIOACTIVE HALF-LIFE
The
ratio of carbon-12 and carbon-14
in a plant or animal is nearly constant
when the organism is alive.
 When it dies, the carbon-14 atoms
decay and the ratio changes
By measuring this ratio, the age of the
organism’s remain can be estimated.

CHECK-IN:
Why
are large nuclei unstable?