1.  Suggested Reading: Pages 72 - 76 Structure of an Atom

2. Structure & Size of an Atom

3.  Proton – a positively charged particle found in the nucleus (about same mass as a neutron – slightly less)  Neutron – a nuclear particle that has no electrical charge (most massive)  Electron – negatively charged particle surrounding the nucleus (least massive) Atomic Particles

4. Subatomic Particles  Subatomic particles include quarks, leptons, bosons, gluons, mesons, muons, and others.

5. J. J. Thomson (1897) Concluded that cathode rays were made of identical negatively charged particles, which were named electrons.

6. Cathode Ray Tube Negative electrode is called the cathode. Positive electrode is called the anode.

7. Rutherford’s Gold Foil Experiment

9.  A very small region located at the center of an atom. Nucleus

10. Atoms vs. ions  In a atom, the number of electrons has to equal the number of protons. Thus making the atom “electrically neutral”.  Ions have either gained or lost electrons.  If gained the ion is negative in charge, if lost the ion is positive.

11. Atomic Number  The number of protons in an atom.  The atomic number is used to identify the element.

12. Mass Number  mass # = protons + neutrons  always a whole number  NOT on the Periodic Table!

13. Nuclear Symbols Mass # Atomic # Hyphen notation: carbon-12  6 Protons, 6 neutrons, 6 electrons

14. *Complete Nuclear Symbols Hyphen notation: chlorine-37  Atomic # = 17  Mass # = 37  # of protons = 17  # of electrons = 17  # of neutrons = 20

15.  Electrons emitted by cathode Cathode Ray Tube  Electrons are forced through a small hole to form a beam of electrons  Electron beam is bent as it is pulled toward a magnet … you can see it because it ionizes a gas in the tube that glows.  Phosphorescent rings glow due to electric current.

16. Rutherford’s Gold Foil Experiment