1. Nuclear Stability

2. Nuclear Forces Nucleons- protons and neutrons
Nuclide- specific nucleus
Strong force holds the nucleus together
acts between nucleons that are very close together
If nucleons are too far apart the repulsion forces are larger than the strong force and the nucleus will fall apart

3. Arrows describe magnitudes of the strong force acting on protons

4. Quarks Smaller parts of protons and neutrons
Six known flavors of quarks- up, down, top, bottom, strange, and charm
Only up and down make protons and neutrons

5. Binding Energy Energy released when nucleons make a nuclide
Energy comes from the conversion of mass to energy.
E=mc2
The mass of the whole is less than its parts
Difference in mass is the mass defect

6. Nuclear Stability Find the N/Z ratio
N = # neutrons
Z = # protons
Small atoms- atomic number 20 and under
Ratio =1
Larger atoms- atomic number over 20
Ratio =1.5
More neutrons are needed between the protons
Magic numbers of protons and neutrons are stable
No atoms with atomic numbers larger than 83 and mass number bigger than 209 are stable

7. Magic Numbers Nuclear shell model
Nucleons exist in energy levels (shells) in the nucleus
Numbers of nucleons that represent completed nuclear energy levels- 2, 8, 20, 28, 50, 82, and 126- are magic numbers

8. Example:
10B
11B
194Hg
202Hg

9. Rules for Predicting Stability
Except for hydrogen-1and helium-3, in stable nuclei, #neutrons ≥ #protons.
A nucleus that has an N/Z number that is too large or too small is unstable
Nuclei with even numbers of neutrons and protons is more stable
Nuclei that have so-called magic numbers of protons and neutrons tend to be more stable
No atoms that have atomic numbers larger than 83 and mass numbers larger than 209 are stable