1. ATOMIC STRUCTURE CONTINUED
Introduction to
Nuclear Chemistry

2. I can describe a stable/unstable nucleus and explain the different forms of nuclear decay.

3. A BRIEF HISTORY OF NUCLEAR CHEMISTRY
At the end of the 1800s, scientists discovered that certain elements naturally gave off rays of energy. By the early 1900s, scientists began to believe that the nucleus of the atom, though it was extremely small, could produce a tremendous amount of energy.
By the late 1930s, scientists began to realize that atoms could potentially be used to create a weapon of unbelievably destructive power.
As World War II began to expand, Albert Einstein wrote a letter to President Roosevelt stating that the US must pursue a nuclear weapon before the Germans or other enemies could if America was to win the war.

4. A secret project code named the MANHATTAN PROJECT was developed to pursue the creation of an atomic weapon.
The result was the creation of two very powerful atomic bombs named FAT MAN and LITTLE BOY which were used against the cities of HIROSHIMA and NAGASAKI, JAPAN, effectively bringing World War II to an end.
In this unit, we will explore the basic principles of nuclear chemistry.

5. Stability of the Nucleus
Most atoms have a very stable nucleus
it does not change over time.
This stability is due to a force called the STRONG NUCLEAR FORCE.
This force is created by NEUTRONS in the nucleus.
It is not well understood but effectively shields the force of repulsion between the protons in the nucleus.

6. What is an UNSTABLE NUCLEUS?
Some ISOTOPES of an element are naturally unstable. In nuclear chemistry we refer to different isotopes as NUCLIDES.
Too few or too many No makes the nucleus unstable.
Over time, it breaks apart, releasing particles and/or energy.

7. What happens to an UNSTABLE NUCLEUS?
An UNSTABLE nucleus breaks apart bit by bit, releasing particles and energy along the way.
This PROCESS is RADIOACTIVE DECAY.

8. Types of RADIOACTIVE DECAY
Over time, an unstable nucleus will break down until it reaches a stable form.
There are 3 types of RADIOACTIVE DECAY:
Alpha [ α ] (make a fish sign)
Beta [ β ] (make a “B” with a long side)
Gamma [ γ ] (just make a “Y”)

9. What Happens In Alpha Decay?
During ALPHA DECAY, a small piece of the nucleus breaks off and flies away.
This “piece” of the nucleus consists of:
2 Protons and 2 Neutrons and is called an ALPHA PARTICLE!

10. What happens to a nucleus that has LOST an ALPHA PARTICLE?
Once an ALPHA PARTICLE is LOST, the nucleus of the atom is changed, and is transformed into an atom of another element!
This is called a TRANSMUTATION!

11. PROBLEM
What would happen if a URANIUM-238 atom underwent ALPHA DECAY? Some needed information: 1. The chemical symbol of Uranium is “U”. 2. The Atomic Mass Number of this isotope is 238, so the it is written on the UPPER LEFT side of the chemical symbol:. 238 U 3. On the PT, the Atomic Number of Uranium is 92, so it is written at the LOWER LEFT of the chemical symbol: 238 U 92

12. What’s Left After An Alpha Decay
In an ALPHA DECAY, 2 P+ and 2 No leave the nucleus.
Since the Atomic Mass Number is P+ + No = = 4
So the Atomic Mass Number decreases by 4.
In an ALPHA DECAY, 2 P+ leave, so the Atomic Number which equals the number of P+, decreases by 2.
To determine the new element:
SUBTRACT 4 from the top number.
SUBTRACT 2 from the bottom number.
238 U  234
Now look this element up on
the periodic table and write its
chemical symbol as the new
element.

13. 238 U - 4 234 Th 92 - 2 90 So in Alpha Decay Uranium changes into Thorium.

14. Practice Problems
For each of the following ISOTOPES, determine the ALHA DECAY product (use periodic table):
Lead Pb -4
Neptunium Np -4
Astatine At -4