What’s Going on in There? Subatomic Particles Vocabulary: nuclear model proton vacuum neutron electrode J.J. Thomson electron cathode ray tube (CRT) Thomson’s experiment Plum Pudding Model Robert Millikan Oil Drop Experiment Ernest Rutherford Gold Foil Experiment nucleus “The Kiss”, Gustov Klimt, 1908

- + Take a look Facts: The tube contains a vacuum. There is a positive electrode on one side of the tube and a negative electrode on the other side of the tube. The electrodes are hooked up to a 10,000V electrical source. A magnet is the object in the person’s hand. - +

So what’s going on in there? Take a look So what’s going on in there?

Take a look

J.J. Thomson (1897 / England) Thomson concluded that the beam contained “corpuscles” that were small particles inside atoms and were negatively charged. We now call them electrons Thomson knew atoms were neutrally charged, but couldn’t find the positive particle.

Cathode Ray Tube, CRT, demonstrated properties of electrons Thomson’s Experiment Cathode Ray Tube, CRT, demonstrated properties of electrons

Thomson’s Atomic Model Determined that the negatively charged particles have same mass and amount of charge regardless of the type of atom. Developed the “Plum Pudding” model of the atom with negative electrons in positive sphere.

Robert Millikan (1909 / America) Used “Oil Drop” experiment to find the charge of the electron (q = 1.60x10-19 C) He did this by carefully balancing the gravitational and electric forces on tiny charged droplets of oil suspended between two metal electrodes.

Ernest Rutherford (1911 / England) That’s good stuff! Used Gold Foil Experiment He knew that atoms had positive and negative particles, but could not decide how they were arranged. Conducted an experiment to isolate the positive particles in an atom. Decided that the atoms were mostly empty space, but had a dense central core.

Gold Foil Experiment

Ernest Rutherford’s “Nuclear” Atomic Model Dense, positive nucleus surrounded by negative electrons

James Chadwick (1932/ England) Mass of atom was too high to contain only protons and electrons

James Chadwick (1932/ England) The unknown radiation emitted from the beryllium had no charge but the same mass as the protons. Must be an undiscovered neutral particle in the atom. This was the neutron.

James Chadwick’s Atomic Model Revision of Rutherford’s Nuclear Model

electron e- elec. cloud -1 1/1840 9.11 X 10-28 proton p nucleus +1 1 Particle Symb Location Relative charge Relative mass (amu) Actual mass (g) electron e- elec. cloud -1 1/1840 9.11 X 10-28 proton p nucleus +1 1 1.67 X 10-24 neutron n