1. Section 4.2 Subatomic Particles and the Nuclear Atom

2. Objectives • Distinguish between the subatomic particles in terms of relative charge and mass • Describe the structure of the nuclear atom, including the locations of the subatomic particles

3. Discovery of the Atom and its Particles

5. Cathode Ray • Ray of radiation originating from the cathode (-) end of the tube • Stream of negatively charged particles

6. J.J. Thomson’s Plum Pudding Model • English • First hint atom is made of smaller particles.

7. Plum Pudding Model • Atoms were made from a positively chargedsubstance with negatively charged electrons scattered about • Raisins in pudding

8. Thomson’s Ideas • Negative charges came from within atom • Particle smaller than atom exists • Atom divisible!

9. Rutherford’s Gold Foil Experiment • Firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick)

10. Most of the alphas passed through without changing course • Some alphas bounced away from the gold sheet • positive charges repel positive charges

12. Rutherford’s Conclusions • Gold atoms were mostly open space • Not plum pudding! • Atom had a small, dense, positively charged center that repelled his alphas • “Nucleus” • Nucleus is tiny compared to the atom as a whole

13. Rutherford

14. Subatomic Particles • Proton- positively charged; in nucleus • Neutron- no charge; in nucleus • Electron- negatively charged; orbit nucleus; make up volume of atom

16. Assignment • For each of the following, give a description of their theory/model. Include the date: • Aristotle • Democritus • Dalton • Thomson • Rutherford