1. Nuclear Chemistry
Essential Question: How do we determine stability of a nucleus to compare different atoms?

2. TN Science Standards Chemistry I : Standard 1 – Atomic Structure
CLE Describe an atom in terms of its composition and electron characteristics.
Determine the number of protons and neutrons for a particular isotope of an element.

3. Mass Defect
The difference between the mass of a nuclide and the sum of masses for all of its protons, neutrons, and electrons
The atom always has less mass…why?
Consider

4. Mass Defect Sum total mass of all particles in
2 protons (2 x amu) = amu
2 neutrons (2 x amu) = amu
2 electrons (2 x amu) = amu
________________________________________
total mass of all particles =

5. Mass Defect Sum of parts is 4.032979 amu
Isotope’s relative mass is amu
Mass defect = difference amu
What happened to the “missing” mass?

6. Nuclear Binding Energy
The energy released when a nucleus is formed from protons and neutrons
Considered the energy required to hold a nucleus together
More energy released = more stable nucleus!
So what is the source of this energy released from the nucleus?

7. Nuclear Binding Energy
Recall
E=mc2
Mass defect
amu from converts into
4.54 x Joules of nuclear binding energy

8. Nuclear Binding Energy
Binding energy is used to compare stability of different nuclides
The total nuclear binding energy calculated from mass defect with E=mc2 is divided by mass number and graphed

9. Nuclear Stability A graph of stable nuclei cluster along a narrow band
n° : p+
1.5 : 1
For Z ˃ 20
A graph of stable nuclei cluster
along a narrow band
Called the “Band of Stability”
Notice two slopes…
Black line m=1 for small atoms
Red line m= 1.5 for larger atoms
(A-Z)/Z = 1.5
n° : p+
1 : 1
For Z ˂ 20

10. Nuclear Stability Stable nuclei have even mass numbers
Most have even numbers of both protons and neutrons
Magic Numbers 2, 8, 20, 28, 50, 82, and 126
These numbers of p+, n°, or both are most stable by completing nuclear energy levels

11. Nuclear Stability
Unstable nuclei spontaneously decay to become more stable
Nuclear Reaction a reaction that changes a nucleus of an atom
Transmutation a change in the identity of an atom when the number of protons are changed