Section 4 2 Subatomic Particles and the Nuclear

Section 4. 2 Subatomic Particles and the Nuclear Atom

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

Discovery of the Atom and its Particles

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

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

Plum Pudding Model l Atoms were made from a positively charged substance with negatively charged electrons scattered about l Raisins in pudding

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

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

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

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

Rutherford

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

Particle Charge Mass (amu) Proton +1 1. 0073 = 1 Neutron 0 1. 0087 = 1 Electron -1 5. 486 x 10 -4 = 0

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