>> host: Welcome back
to Chemistry Matters
and our unit
on nuclear chemistry!
With a solid understanding
of atomic structure
and radioactivity,
let's now look at how atoms
can break apart
in nuclear fission
to make different elements.
In our classroom
cloud chambers, you were able
to see paths left
by subatomic particles
being emitted from atoms.
We call this
radioactive decay.
When a radioactive atom decays,
there are three important
products: Alpha particles,
Beta particles,
and Gamma radiation.
The other particle
that remains after nuclear decay
is called the daughter nuclide.
Let's take a look at
how Alpha, Beta and Gamma
decay occur.
Here is a diagram
of a Uranium-238 atom.
It undergoes Alpha decay,
producing one Alpha particle
and a daughter nuclide.
As you can see here,
the Alpha particle is made up
of two protons
and two neutrons.
It's essentially
a helium nucleus,
without the electrons,
giving it a 2+ charge.
You'll recall Alpha particles
from Unit 3,
when we studied Rutherford's
gold foil experiment.
The Alpha particles
were deflected in unexpected
ways, which led Rutherford
to identify the nucleus
of the atom.
And as you know from
the last video on the Unit 11
playlist, an isotope
is defined as atoms
of the same element
with different numbers
of neutrons.
Isotope notation
is a common method
for communicating information
about a single atom
or radioactive particle.
So this is a good time
to learn how to write
isotope notation to represent
radioactive particles.
Let's use a familiar atom
to show you what I mean.
To write the isotope
for one sodium atom,
first write the chemical symbol
for sodium, Na.
On the lower left,
write the number of protons,
known as the atomic number,
as a subscript
before the symbol.
For Sodium,
the atomic number is 11.
The mass number,
total mass of the protons
plus neutrons, is written
as a superscript
before the symbol.
For sodium,
the mass number is 23.
Even though you know
that sodium forms
a positive ion,
we do not typically show
the charge of the atom
in isotope notation format.
Isotope notation
is all about the nucleus,
not what's happening
outside the nucleus.
And sometimes this notation
will exclude the atomic number,
since you can easily
find that number
on the periodic table
from the symbol.
With that in mind,
let's write the isotope notation
for an Alpha particle.
Remember that
an Alpha particle is made of
two protons and two neutrons,
so an Alpha particle
is one helium nucleus.
To represent
an Alpha particle,
just start with
the element symbol for helium,
He, in the center.
The atomic number of Helium
is 2, so write that
as a subscript
before the symbol.
The mass number is 4,
so write that as a superscript
before the symbol.
Notice again that
we didn't place the charge
of +2 in the top right corner.
Many scientists prefer to use
the Greek letter Alpha
to represent the Alpha particle.
And there are actually
three accepted ways
to represent this particle.
The Greek letter Alpha
I just mentioned,
or the Greek letter Alpha
with the atomic number
and mass number,
or the helium symbol
with the atomic number
and mass number.
Now, let's try using
isotope notation to write
a balanced nuclear equation.
A radioactive material
that's probably in the room
with you right now
is Americium-241.
You'll find it's a very
important part of common
household smoke detectors.
To draw the proper isotope
notation of Americium-241,
find the element symbol for
Americium on the periodic
table, Am.
Write that down.
Now write its atomic number
on the lower left.
Americium has 95 protons.
The mass number
of Americium-241 is found
in its name.
So, write 241 as the mass
number on the upper left.
When a radioactive atom,
like Americium-241,
undergoes Alpha decay, it
releases an Alpha particle.
The Alpha particle,
composed of two protons
and two neutrons,
goes flying away.
Remember, this is the symbol
for the Alpha particle,
a mass number of 4
and an atomic number of 2.
But what about the rest
of the protons and neutrons
in the Americium-241 atom?
As you know from unit 5,
the Law of Conservation
of Matter says matter
cannot be created or destroyed.
So something had to happen
to the rest of the protons,
neutrons and electrons of
the Americium-241 atom.
In fact, aside from
the 2 protons and 2 neutrons
that were emitted with
the Alpha particle,
they're all still there,
just in a nucleus
that's now smaller.
This new nucleus that's
left behind is what we call
the daughter nuclide.
It's what's left after
the Alpha particle is emitted.
Notice that after
undergoing Alpha decay,
the daughter nuclide has lost
two protons, so it only has
93 protons remaining.
Therefore, it's not
Americium anymore.
Check the periodic table.
What element has 93 protons?
It's Neptunium,
and the element symbol is Np.
Now, what's the mass number
of this new Neptunium atom?
Since the atom lost
four nuclear particles,
two protons and two neutrons,
subtract four from
the mass number of Americium.
241 minus 4 equals 237.
So write 237
as the mass number of
the daughter nuclide, Neptunium.
You have now completed
your first nuclear equation!
As with any equation
in chemistry,
the Law of Conservation
of Matter that you learned
about in Unit 5 applies.
Notice how the mass numbers
on the right side add up
to 241, and that equals
the mass number
on the left side.
We can also add up
the atomic numbers
in the same way.
95 on the left side,
and a total of 95
on the right side.
The second product that can
be caused by radioactive decay
is a Beta particle.
You can think of it simply
as an electron.
We represent it
with a Greek letter Beta,
a B shape with a little tail.
Here's what happens
during Beta decay.
One neutron
turns into one proton.
The atom therefore gains
a proton, loses a neutron,
and releases an electron
that we call a Beta particle.
It's not one of the electrons
that was in energy levels
around the atom.
It's a Beta particle,
a new electron made when
a neutron actually changed
into a proton.
It'll help you understand this
by learning how to write
the isotope notation
for a Beta particle.
So let's write the isotope
notation for one
Beta particle.
Start by writing
the Greek letter Beta,
or if you prefer, you can
just write "e" for electron.
The mass number will be 0
since there are no protons
or neutrons.
Write the mass number
at the top left.
Now here is something
strange that happens
in Beta decay.
The only way for
a Beta particle to form
is for a neutron
to turn into a proton.
Chemists assign
the atomic number negative one
as the atomic number
of a Beta particle.
So, write -1 on the lower
left as the atomic number
of the Beta particle.
I realize that you have not
heard about this in any
of our previous units.
That's because nuclear chemistry
is different in many ways
from the other forms
of chemistry you've studied.
Now let's write the nuclear
equation for the Beta decay
of the isotope carbon-14.
Carbon has an atomic number
of 6, and this radioactive
isotope of carbon has
a mass number of 14--
6 protons and 8 neutrons.
When Beta decay occurs,
one neutron turns into
a proton.
The atom has one more proton
than it did before,
changing the atomic number
to 7.
The atomic mass is still
14-- 7 protons
plus 7 neutrons.
Which element has
an atomic number of seven?
The periodic table
has the answer.
It's Nitrogen.
The daughter nuclide
is nitrogen-14, and
a Beta particle is emitted.
Add the mass numbers
and the atomic numbers
on each side to ensure
that they're equal.
The atomic number
on the left is six.
The atomic numbers on the right
are seven and minus-1.
And seven plus a negative one
equals six.
The atomic mass on the left
is a total of 14.
On the right, the mass number
is 14 plus 0,
which equals fourteen.
So our nuclear equation
balances.
The third product
of radioactive decay
that we know about
is Gamma radiation.
Gamma radiation
is energy, and as you know,
energy is not matter.
So when Gamma decay occurs,
an atom emits
very powerful energy.
We represent Gamma radiation
with the Greek letter Gamma,
which kind of looks like
a fancy "Y."
The isotope notation for
the Gamma radiation shows
that it has no mass
and no atomic number,
because it's radiation,
which is energy.
Gamma radiation is emitted with
all types of radioactivity.
They're the energy released
along with an Alpha
or Beta particle,
to make the radioactive nucleus
more stable.
This equation shows
the Gamma decay of Thorium-230.
You can tell that
the Thorium atom undergoes
Alpha decay because you can
see the Alpha particle
on the right hand side
of the nuclear equation.
The daughter nuclide is now
Radium 226, an element
with two less protons
than Thorium.
And what does
this Greek letter Gamma mean?
It lets us know that Gamma
radiation was released
as part of this Alpha decay.
We usually call this
a Gamma emission.
Gamma radiation is very
high energy with no mass.
And since it's a type of
light energy, it travels
very quickly.
Technically at...
well, the speed of light.
Because of its energy and
speed, it can also be
damaging, because it can
penetrate human tissues.
So now is a good time
for an explanation of how to
shield yourself from
different kinds of radiation.
Alpha particles
are the heaviest
radioactive particles,
and also the slowest.
You can be shielded
from Alpha particles easily
by thin metal foils,
skin, or even paper.
Beta particles are slower
and have less energy
than Gamma rays, but are
faster and more energetic
than Alpha particles.
Beta particles cannot
penetrate metal sheets
at least a half-centimeter
thick, or dense wood,
or even heavy clothing.
Gamma rays carry the most
energy of the 3 radioactive
decay products.
Thick concrete or lead
is needed to shield,
or stop, Gamma rays.
Okay, that was a lot
to take in.
This chart
summarizes it nicely.
It's a graphic organizer
for helping you remember
the characteristics
of Alpha particles,
Beta particles,
and Gamma rays.
And it's available in our
Chemistry Matters Toolkit.
So now, to take a more
in depth look at
nuclear equations,
and get a different look
at carbon-14,
let's get back to
our classroom to see
how we can model
these processes
and practice using them!
>> professor: At this point
in this unit, it will be
really helpful to build
nuclear models so we can
make sure we understand the
forms of radioactive decay:
Alpha, Beta and Gamma.
I'll put the periodic table
on the monitor.
Use your magnetic model kits
to build a carbon-14 nucleus.
And because
we're working in the realm
of nuclear chemistry,
which is concerned with
the nucleus of the atom,
not the electrons, you don't
need to show the electrons
in these models.
>> student: Okay, carbon has
6 protons, so I'll put
6 protons in the nucleus.
>> student: And on the
periodic table, it says
carbon has an atomic mass
of 12.01, so the mass
number of the most common
isotope must be 12.
I'll add 6 neutrons, right?
>> student: Wait!
We're supposed to build
carbon-14.
That means the mass number
is 14, so there's actually
8 neutrons, not 6.
>> student: Oh yeah!
Six protons plus
eight neutrons gives us
a mass number of 14.
carbon-14 is an isotope
of carbon.
>> student: Good.
I'll add 8 neutrons.
There!
A carbon-14 nucleus.
>> student: That's what
we got, too!
>> professor: Good!
You've both built your
carbon-14 nuclei.
Now try to show what happens
when your carbon-14
undergoes Beta decay.
>> student: I'll try.
A Beta particle is emitted
when a neutron suddenly
changes into a proton.
Then the Beta particle,
the electron,
is released.
>> professor: Good!
Now count the number
of protons and neutrons
you have in your new nucleus.
>> student: Well, we have
seven protons now.
>> student: And one neutron
changed into a proton,
so we only have
seven neutrons now.
>> professor: Exactly.
The Law of Conservation
of Matter reminds us
that mass and matter, they can't
be created or destroyed.
So, although we're showing
an atom undergoing decay,
the total mass of
the reactants and products
in the nuclear equation
will stay the same.
Now that the atom
has lost a neutron
and gained a proton,
what's the new mass number?
>> student: Well, one neutron
changed to a proton.
So if the old mass number
was 14,
the new mass number
will still be 14.
>> professor: Right!
And now that our atom
has gained a proton,
what else has happened?
>> student: It's not
carbon anymore!
Carbon has to have
six protons to be carbon.
>> professor: Exactly!
So what is the new atom?
You can look at our
periodic table for help.
>> student: Well, our new atom
has 7 protons, which means
it has an atomic number
of 7, so the carbon-14
has changed into nitrogen-14!
>> professor: Good job!
Now, let's practice writing
this out in an equation.
This is a great way to
visualize the same reaction
but in a different way.
Use your whiteboards to do this.
Let's start with
a carbon-14 nucleus.
The symbol for carbon is "C,"
so write a "C."
The mass number is 14,
so put a 14 in the upper
left hand corner.
The atomic number is 6,
and that goes in the bottom
left hand corner
underneath the 14.
Then we want to represent
carbon-14 going through
Beta decay. Now decay
is like decomposition.
It's breaking down,
so there are no other
reactants.
But we need to know
the other products.
We know it was Beta decay,
and that means a neutron
was converted into a proton.
>> student: That still seems
so strange to me--
a neutron turning into
a proton.
>> professor: I agree.
Nuclear chemistry
is very different
from the other chemistry
we've studied so far
in this course,
but for the scope of
this course, it isn't
necessary to explain exactly
how this transformation occurs.
But you should know that
many scientists are trying
to answer this question
right now.
For our purposes, you know
that a neutron turns into
a proton during Beta decay.
So, can you show an equation
in which the daughter nuclide
formed after the neutron
has been changed into a proton?
>> student: Well, we had
six protons and eight neutrons.
One neutron changed
into a proton.
That left us with seven
protons and seven neutrons.
>> student: So our mass number
stays 14, and the 7 goes
below it to represent
the atomic number.
>> student: That means
our equation needs to include
a nitrogen atom, right?
>> professor: Yes, but why?
>> student: Because nitrogen
contains seven protons
and that's what
the daughter nuclide has.
>> professor: Good.
But what else happens?
>> student: Well,
a Beta particle is released
from the nucleus.
>> student: And a Beta particle
is just an electron.
>> professor: Right.
So add that Beta particle
to your equation.
Good.
There's a mass number of 0,
and an atomic number of -1,
which help to balance
the equation-- a total
mass number of 14
on both sides,
and a total atomic number
of 6 on both sides.
Well done, both groups.
Now that you have a better
understanding of nuclear
decay, try writing
the following two
nuclear decay equations:
First of all, represent
nitrogen-15 going through
Beta decay.
And then Uranium-235
going through Alpha
and then Beta decay.
Based on what you now know
about nuclear reactions,
write the nuclear decay
equations
for these two scenarios
using isotope notation.
And don't forget,
both processes
will be accompanied
by Gamma radiation.
So you'll need to include that
on your board as well.
>> host: We'll take a break
here to let you get started
with practice writing
nuclear equations
using isotope notation
for the two examples
our teacher just gave us.
Remember, you need to write
the complete nuclear equations.
If you need additional
practice, you can find
additional practice problems
in our Chemistry Matters
Toolkit.
When you're done,
join us at the top
of the next video on
the Unit 11 playlist, where
we'll see how your equations
compare to those
of our students.