1. Ch. 4.2 Structure of the Nuclear Atom

2. Subatomic Particles Three types: electrons, protons, and neutrons.
Electrons discovered in 1897 by J.J. Thomson.
Negatively charged subatomic particles.
Discovered by passing electric current through low-pressure gas chamber, with metal plates (electrodes) at both ends.

3. One electrode became positively charged, the other negatively charged.
Produced a glowing cathode ray beam.
Beam could be deflected by magnets; conclusion was the beam was made of tiny charged particles, called electrons.
Experiments confirmed charge-to-mass ratio of electron; later confirmed by Millikan.
Mass is 1/1840th of a hydrogen atom.

5. Protons and Neutrons
If atom loses electrons, what happens to rest of the atom?
Goldstein discovered oppositely moving beams in the cathode ray tube (canal rays) were made of subatomic positively charged particles….protons.
1932-James Chadwick confirmed existence of particle with no charge but mass similar to proton…the neutron.

6. Rutheford’s Gold Foil Experiment
In 1911, Rutherford directed a beam of alpha particles (positively charged helium nuclei) at a thin sheet of gold foil, expecting them to easily pass through with slight deflection due to positive charges spread throughout the atoms.
Most passed through without deflection. Some deflected at sharp angles, others bounced straight back!

9. Results suggested atom was mostly empty space, with a small massive positively charged nucleus.
Rutherford model is called the nuclear atom. Protons and neutrons in the nucleus. Electrons distributed around the nucleus, making up almost all the atom’s volume.