Beaker Breaker!!

1. In oxides of oxygen such as dihydrogen oxide and hydrogen peroxide, atoms combine in small, whole-number ratios. This evidence supports what law?

2. Beaker Breaker!! • Who believed that the world is made up of empty space and of atoms? ____________________ • Who believed that matter is continuous and not made of atoms?__________________ • Which law states mass is neither destroyed nor created during chemical reactions?________________ • True or False Dalton believed that atoms can be divided into smaller parts________

3. 3-2: • The Structure of the Atom

4. Objectives • Summarize the observed properties of cathode rays and how they relate to the electron • Summarize Rutherford’s experiment and how they relate to atomic structure • List the properties of protons, neutrons and electrons

5. Early Research on Atomic Particles Eventually exceptions were discovered to Dalton’s Atomic Theory……..

6. Cathode Ray Studies of the mid 1800’s

7. See Figure 3-4 p.70 • Cathode: negative electrode • Cathode ray: glowing ray that comes from cathode when electric current was passed through a tube of gas under low pressure…what was the source?

8. Cathode tube experiments showed: • See top page 71 • Object in path of ray casts a shadow • Paddle wheel on rail inside cathode tube would roll • Rays were deflected by magnetic fields • Rays were deflected by negatively charged objects

11. What did these observations mean? • Glowing ray in cathode tube was made of particles • Particles that composed cathode rays are negatively charged

12. 1897 J.J. Thomson Further studied cathode rays and concluded: • cathode ray particle had a very large charge for its tiny mass • All cathode rays are composed of identical negatively charged particles, regardless of metal used as cathode • Particles later called ELECTRONS • first to say “cathode ray” was a building block of the atom – ATOM WAS NO LONGER INDIVISIBLE!

13. "At first there were very few who believed in the existence of these bodies smaller than atoms."

14. Thomson (con’t) • “PLUM PUDDING” Model because atom was thought to consist of electrons moving about in a sphere of positive charge

15. Robert Millikan • OIL DROP EXPERIMENT

16. An atomizer sprayed a fine mist of oil droplets into the chamber. Some of these tiny droplets fell through a hole in the upper floor. Millikan first let them fall until they reached terminal velocity. Using the microscope, he measured their terminal velocity, and by use of a formula, calculated the mass of each oil drop. • Next, Millikan applied a charge to the falling drops by illuminating the bottom chamber with x-rays. This caused the air to become ionized, and electrons to attach themselves to the oil drops. • By attaching a battery to the plates above and below this bottom chamber, he was able to apply an electric voltage. The electric field produced in the bottom chamber by this voltage would act on the charged oil drops; if the voltage was just right, the electromagnetic force would just balance the force of gravity on a drop, and the drop would hang suspended in mid-air.

18. Robert Millikan • Determined thecharge on an electron in his famous OIL DROP EXPERIMENT

19. Combining the work of Thomson and Millikan -------> • Thomson: charge/mass ratio of an electron • Millikan: charge on an electron • Together: determined the mass of an electron • 1/1837 lightest atom (H)

20. Beaker Breaker!! • What was the name of the instrument used to first discover the negative particles called electrons? • What was the name of J.J. Thompson’s model of the atom? • Millikan’s famous oil drop experiment discovered the__________of an electron. • True or False Millikan believed that atoms can be divided into smaller parts________

21. Work with modified cathode ray tubes found rays moving in the opposite direction that had a positive charge - now called PROTONS (early l900’s) • 1930’s: verification of a 3rd atomic particles with high energy,no charge and mass about the same as a proton - NEUTRONS

22. Discovery of these 3 subatomic particles called for major revisions in Dalton’s Atomic Theory….. (atoms could be broken into smaller particles!)

23. Rutherford, 1912 • Gold FOIL experiment

25. Observations of Rutherford’s Gold Foil experiment • Most positive particles passed through the gold foil • About 1 in 8,000 particles bounced almost straight back

26. Rutherford “NUCLEAR MODEL” • As a result of his gold foil experiments, he concluded that • atom is mostly empty space • atom consists of a small, positively-charged “core” (nucleus) surrounded by electrons • Radii of most atoms: 40 --> 270 pm (10-12m) Radii of nuclei: only 0.001 pm Density of nuclei: 2 x 108 tons/cm3 !!!!!!!!!!!!!!!

27. Good analogy….. • If the nucleus were the size of a ping pong ball, the electron would be found…. • 0.8 mile away ! (Homestead Rd & 322 intersection to Don’s Pier)

28. Composition of Nucleus • Proton • Positive charge (equal in magnitude but opposite in charge to an electron) • Mass: 1.673 x 10-27 kg • Neutron • Electrically neutral • Mass: 1.675 x 10-27 kg (slightly larger than proton)

29. The number of protons in an atom’s nucleus determines that atom’s identity (Atomic number, Z)

30. Periodic Table Atomic Number Search! • What is the atomic number of Sodium? • What is the atomic number of Zinc? • My Atomic number is 14, who am I? • My Atomic number is 92, who am I? • What is the atomic number of Ca? • What is the atomic number of Au?

31. Good summary table of subatomic particles on page 74

32. NUCLEAR FORCE: short-range proton-proton, neutron-neutron and proton-neutron forces that hold the nuclear particles together

33. Objectives • Summarize the observed properties of cathode rays and how they relate to the electron • Summarize Rutherford’s experiment and how they relate to atomic structure • List the properties of protons, neutrons and electrons