1. Atomic Theory
Nuclear Changes

2. Review of Changes in Nature
Remember from Unit 1 that there are three types of changes in nature.
They are Physical, Chemical, and Nuclear

3. Physical Changes
These are changes in the size, shape, appearance, etc – but with no change in the chemical identity of what you have.
You still have the same stuff…
Examples of these changes are cutting paper with scissors, demolishing a building, boiling water, breaking a piece of glass.

4. Chemical Changes
These are changes in size, shape, appearance, etc – but here you do see the formation of new substances that were not previously in the system.
But – all of the atoms retain their chemical identity – they are simply connected to different atoms than they were before the change.
Examples here are burning paper, explosions, mixing two solutions to form a precipitate, milk going sour, biological decay, leaves changing color, and metals being consumed by acids.

5. Now for Nuclear Changes
These are changes in the internal structure of the atoms themselves.
The numbers of protons and neutrons are changed.
The end result here is that you get new atoms of different elements.

6. Nuclear Changes
We defined these changes as “changes to the internal structure of the atoms”.
What we looked for was a statement that described “one element turning into a different element”.
While it is true that we “get new stuff” in these reactions, they are not classified as chemical changes because they DO NOT follow the Law of Conservation of Mass (like all chemical changes do).

7. Two Domains of Nuclear Changes
Fission – these are nuclear changes in which a single atom is split into two or more smaller atoms.
Fusion – these are nuclear changes in which two or more smaller atoms become joined together to produce a larger atom.

8. Fission - Alpha Decay He 4 2
An alpha particle is simply a helium – 4 nucleus. It has 2 protons and 2 neutrons.
We represent it like this:
This is the first of the nuclear change processes.
In this scenario, an unstable nucleus emits (means it “spits out”) an alpha particle. He 4 2

9. Nuclear Equation
This is the chemist’s method of representing a nuclear change in a format that looks like a chemical equation.
Example: “Write the nuclear equation for the alpha decay of Uranium-235”.

10. How to do this… The starting point is given – it is the Uranium-235.
Since the example indicates that this is an alpha decay, the 1st product in the equation will be an alpha particle.
The only task will be to determine the identity of the other product.
So…writing what we know so far…

11. Gives this… U
235 92 He 4 2 + ?
To determine the identity of the other product, we have to subtract the 4 from the 235 to get the new mass number and then subtract the 2 from the 92 to find the new atomic number.
Once we have the new atomic number, we can use the periodic chart to find its atomic symbol.

12. Doing all of that gives us:
235 92 He 4 2 + Th
231 90
Every single alpha decay produces an alpha particle as the first product and then you have to figure out the identity of the other product.

13. Fission - Beta Decay
This is the other type of nuclear decay that we have to know.
In this scenario, an unstable nucleus emits a beta particle (makes sense!).
A beta particle is a high energy electron and we indicate it like this: β -1
The “0” is because the electron has no mass (remember from the discussion on the “amu”) and the -1 is because the electron has a negative charge.

14. Nuclear Equation for a Beta Decay
Consider this example: “The isotope iodine – 125 undergoes beta decay. Write the nuclear equation for the process.”
So… proceeding like we did for the alpha decay example – we know the starting point (the iodine-125) and we know that the 1st product will be a beta particle. That gives us this: I
125 53 β -1 + ?

15. Doing the same sort of subtracting:
125 53 β -1 + ?
ends up as I
125 53 β -1 + Xe
125 54
Careful on the subtraction on the bottom numbers…

16. Gamma Radiation This is a third “product” of nuclear decay.
It is pure wave energy – no particle here.
The symbol for gamma radiation is:
Note that it has no mass or atomic number – so including it into equations is essentially a waste of time.

17. Your assignment:
Complete the worksheet that will be provided by the teacher.
Use the periodic chart to determine the atomic symbols that go with the atomic numbers.

18. “Penetrating Strength”
This is a concept that came out of the cold war in US – World history.
Basic idea was to understand what could be used to shield us from nuclear decay particles.
A basic summary is that:
alpha < beta < gamma
Very important to note that gamma radiation accompanies all other decay processes.

19. Bombardment This is a process for causing nuclear decay events.
A “nuclear bullet” - a neutron - is fired into a nucleus causing fission events.
You will have to be careful on the math when trying to work through these equations.