Download Some isotopes - Red Hook Central School District

Nuclear Chemistry
“regular” chemistry involves only the ELECTRONS in atoms
All the rest of this year we will be studying
only “regular” chemistry
“nuclear” chemistry involves only the NUCLEUS in atoms
In this chapter (and only this chapter) we will be studying
“nuclear” chemistry
Important Reminder!
• Every atom of the same element must have the
same number of PROTONS in its nucleus
• For example, for Lithium to be Lithium, it must
have 3 protons. An element with only two
protons would be He, with 4 protons Be
• If the number of protons in a nucleus changes,
the atom becomes a different element!
Remember the alchemists?
• They wanted to change Pb (82 protons)
into Au (79 protons)
• To achieve this would have meant
removing 3 protons from the Pb atom’s
nucleus
• Alchemists would have needed to do
NUCLEAR chemistry
Stability of atoms
• All the atoms we have studied so far have
been “stable”. That means they stay the
same and don’t change into other atoms
• Some atoms are not stable. They tend to
“decay” into other atoms.
• Unstable atoms are called
RADIOISOPTOPES
Which atoms are unstable?
• The ratio of protons and neutrons in the
nucleus determines an atom stability
Stable
atoms
# of n = # of p
(1 to 1 ratio)
All atoms with more than
83 protons are unstable
Which atoms are unstable?
• All atoms with more than 83 protons
• Some isotopes of atoms with less than 83
protons do not have the right proton to
neutron ratio to be stable
Remember! An isotope is an atom with
more or less neutrons than other atoms of
that same element
What happens when an unstable
atom “decays” ?
• It emits (gives off) radiation particles.
This means it is radioactive.
• It makes a new atom that is more stable
Types of Radiation particles
• Alpha
• Beta
• Positron
• Gamma Ray
Alpha Particles
α
Greek letter alpha
It is the nucleus of a He atom (no e-)
with 2 protons, 2 neutrons and
a charge of +2
He
4
2
Beta Particles
β or β Greek letter beta
Like an electron except it comes
out of the nucleus, not the e- cloud
has negligible (no) mass
has a charge of -1
Positron Particles
β + Greek letter beta
has negligible (no) mass
has a charge of +1
Like an e- (or β) but with a
positive charge
Gamma Rays
γ Greek letter gamma
High energy particle, like x-rays
no mass
no charge
Penetrating power
When an unstable atom undergoes
alpha decay…..
Parent atom
235
92
231
90
U
Uranium-235
radiation
Daughter product
decays to
Th + He
Thorium-231
4
2
and
an alpha particle
What is happening here?
220
87
Fr
216
85
At + He
4
2
What is happening here?
220
87
Fr
216
85
At + He
4
2
Fr-220 decays to At-216 and an alpha particle
The following unstable atoms
decay by emitting an alpha particle
Ra -226
Rn- 222
Th-232
Look in Table N to find
other atoms whose
decay mode is also
an alpha particle
Write the decay equation for:
Ra -226
Step 1: Re-write the atom symbol so it
includes both atomic mass and
atomic number (look it up!)
Atomic mass
Atomic number
226
88
Ra
Write the decay equation for
Ra-226:
Step 2: Put the unstable atom on the left
side of the decay arrow
226
88
Ra
Radium -226
decays to
Write the decay equation for
Ra-226:
Step 3: Look up decay mode for the atom in
Table N and write that after the decay
arrow
226
88
Ra
Radium -226
4
2
α
decays to alpha
particle
Write the decay equation for
Ra-226:
Step 4: Find the daughter product by
conserving mass and charge
226
226
88
=
Ra
88
Radium -226
4
4
2
=
2
+
222
α+ X
222
86
+
86
decays to alpha and atom X
particle
Write the decay equation for
Ra-226:
Step 5: Identify the daughter product by
looking up its atomic number
in the
periodic table
226
88
Ra
Radium -226
4
2
α + Rn
222
86
decays to alpha and Radon-222
particle
You try it for:
Radon -222
Thorium – 232
Uranium - 233