Fundamental Particles of Matter Electrons Cathode Ray Tube Experiments Millikan oil-drop experiment Davy, Faraday, Stoney, Thomson Protons Rutheford scattering experiment Neutrons -Bombardment experiments Chadwick

Cathode rays Travel in straight lines Negatively charged Have mass Cathode rays = Electron beam Thomson determined the e/m ratio by studying the deflection of the beam in electric and magnetic fields

Millikan Drop analysis Determined the charge (e) on an electron from the experiment e/m = 1.75882*108 C/g from the cathode ray exp. m = 1.75882*108 C/g * e = 9.10940*10-28 g

Canal Rays = Positive (cation) rays Original “Plum Pudding” Model Protons Cathode Ray Tube Experiments Atom  cation+ + e- Canal Rays = Positive (cation) rays H2  2H+ + 2e- Determined the e/m of a proton Rutheford Scattering Experiment Nucleus New Model

An atom is defined by the # of protons Atomic Number Moseley Bombarded Elements with high energy e- Produced different wavelengths for different element Each element differs from the preceding element by having one more proton An atom is defined by the # of protons

Isotopes - Atoms of the same element (have the same # of protons) that have different masses (have differing number of neutrons) Mass number A = Z (#p) + #n Nuclide Symbol E A Z 10 5 11 5 B #n=5 B #n=6

Mass Spectrometry - measures the charge-to-mass (e/m) ratio of Mass Spectrometry - measures the charge-to-mass (e/m) ratio of charged particles. If we put Neon in a mass spectrometer we could determine how many natural isotopes there are for neon and the percent abundance of each isotope 20Ne 90.48% 21Ne 0.27% 22Ne 9.25% atomic mass of Ne = 19.99244*0.9048 + 20.99384*0.0027 + 20.99384*0.925 atomic mass Ne = 20.1979 amu