1. The atom and its nucleus
Nuclear Physics
The atom and its nucleus

2. Discovery of the nuclear atom
1909-Geiger and Marsden, working under Rutherford
Scattering of alpha particles shot at a thin gold foil
Alpha particle 4x mass of H atom
Alpha particles-emitted when unstable elements decay
Used radon – source of alpha particle

3. Rutherford, Geiger, and Marsden
Found that sometimes alpha particles were detected at very large scattering angles
This couldn’t be understood in terms of the prevailing model
Thomson

4. Geiger-Marsden-Rutherford experiment
Deflection indicative of enormous force of repulsion between alpha particle and carrier of positive charge of atom
Positive charge resided on a tiny object
Alpha particle could approach + charge at a small d, and the Coulomb force of repulsion, would be enormous

5. Rutherford model Massive, positively charged nucleus
Electrons orbited nucleus
Force keeping electrons in orbit
Electrical force between negative electron charge and positive nuclear charge
Couldn’t explain why matter is stable, i.e. why atoms exist

6. Bohr model Examined hydrogen
Realized electron could exist in certain specific states of definite energy, without radiating away energy
Electron lose energy when makes transition from one state to a lower
Emitted energy is difference between states
Evidence-emission and absorption spectra

7. Spectra Normal conditions-lowest energy level
Atoms excited  higher level
As soon as they do, transition back down to lower state
Energy allows wavelength of emitted light to be calculated

8. Spectra
Emission spectrum  set of wavelengths of light emitted by the atoms of an element
Send a light of specific wavelength through an atom
Doesn’t correspond to any of the wavelengths
Light transmitted without absorption

9. Nuclear Structure Protons and neutrons
# of protons is Z (atomic number)
Protons + neutrons = mass (A)
Electric charge is Z IeI
# of neutrons N= A-Z
Nucleon
Proton or neutron

10. Isotopes
Nuclei that have the same number of protons, but different number of neutrons
Same number of electrons
Identical chemical properties, different physical
Mass spectrometer

11. Forces within the nucleus
Nucleons bound by nuclear force
Attractive force
Stronger than electrical force if separation between 2 nucleons is small
Larger separation-small force
Nuclear radius
R = 1.2 A1/3 x 10-15m
A is total number of p and n

12. Forces within the nucleus
Weak nuclear force
Responsible for decay of a neutron into a proton
Called beta decay