1. The Nucleus
Topic 16.1

2. Outcomes
There are no outcomes that correspond with this lesson…just some periodic table review.

3. Rutherford
Rutherford’s gold foil experiment demonstrated that atoms contained a densely packed, positive charged core
He called the tightly packed, positive particles protons

4. Discovering the Neutron
Protons could not account for all the mass contained within the nucleus, in fact, the charge-to-mass ratio of a proton was twice that of a helium nuclei
Rutherford suggested that the nucleus may also contain neutrons, neutral particles with about the same mass as a proton

5. Nuclear Definitions
Proton- Positively charged particle in the nucleus (p+)
Atomic number- Number of protons in the nucleus (equal to the number of electrons surrounding the nucleus in a neutral atom)
Neutrons- Particle with no charge in the nucleus (n0)
Nucleons- Number of protons and neutrons collectively
Mass number- Sum of the number of protons and neutrons in a nucleus
Electron- Particle with a negative charge surrounding the nucleus (e-)

6. Nuclear Terms and Notations
Atomic Mass (A): number of nucleons (protons & neutrons)
Atomic Number (Z): number of protons
Element Symbol (X)
Neutron Number (N): number of neutrons (A – Z)

7. Sample Problem
How many protons and neutrons does a carbon atom have?

8. Isotopes Many elements have two or more isotopes
Isotopes: same number of protons, but differing number of neutrons
Their chemical properties are almost identical, however, their physical properties can differ dramatically. Some isotopes are very stable, while others are highly radioactive

9. Atomic Mass Units
Atoms and nuclei, are incredibly small and therefore using kilograms is illogical
For calculations involving subatomic particles the atomic mass unit (u) is used – which is 1/12 the mass of a carbon12 isotope
1 atomic mass unit () = x10-27kg

10. (DON’T THINK OF ‘C’ AS A UNIT – WE MUST APPLY c2)
Converting Mass
The data sheet lists masses in units of MeV/c2.
How do we convert this to kilograms?
Example: An electron is listed as MeV/c2
(DON’T THINK OF ‘C’ AS A UNIT – WE MUST APPLY c2)

11. Homework
p. 167 #1-3