1. + Unit 3 The History of the ATOM and Atomic Structures Democritus & Dalton Thomson Rutherford Bohr Schrodinger

2. + Democritus 460-370 B.C. Greek Philosopher He called nature’s basic particle an atomos, based on the Greek word “indivisible.” Had no evidence, so people didn’t take him seriously. He considers education to be the noblest of pursuits, but cautioned that learning without sense leads to error. (THERE MUST BE A POINT!!!) Aristotle said empty space did not exist & rejected Democritus; said matter was EARTH, WATER, AIR & FIRE

3. + John Dalton 1803 Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms. Element A 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other elements.

4. + Dalton’s Atomic Theory 3. Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds.

5. + Dalton’s Atomic Theory 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

6. + J.J. Thomson 1897 (with Crookes & Millikan) discovery of the electron (e - ) disproved Dalton’s theory; atoms DID have smaller parts after all Used a cathode ray tube to prove that there were charged particles (stream of (-) particles) within the atom

7. + Thomson Model Plum pudding model aka chocolate chip cookie model Millikan found out that electrons were negatively charged and had a mass of 1/1840 of a hydrogen atom

8. + Video Links to Experiments JJ Thomson’s Cathode Ray Tube How does it work? Rutherford’s Gold Foil Experiment What did he do?

9. + Ernest Rutherford 1911 Used alpha particles to shoot at gold foil. Got unexpected results. Something was deflecting particles back to the source. Buried next to Sir Issac Newton and Lord Kelvin in Westminster Abbey.

10. + Nucleus Empty Space Electrons

11. + Rutherford said, “Atoms have a nucleus!” Dense & positively charged Contains most of the mass of the atom Contains the protons (positive charge; heavy) Electrons are around the outside of the nucleus flying around the empty space

12. + Video Links to Experiments JJ Thomson’s Cathode Ray Tube How does it work? Rutherford’s Gold Foil Experiment What did he do?

13. + James Chadwick Discovered the neutron in 1932 Has a neutral charge Found in the nucleus About ½ of the mass of the nucleus Wanted to know where the extra mass was coming from in an atom; shot particles @ beryllium Eventually led to experiments to bombard atoms with neutrons –> uranium  bombs!

14. + Niels Bohr - 1913 Created the Bohr model Electrons travel in definite orbits/ energy levels around the nucleus aka “Planetary Model” – orbit the nucleus like planets around the sun Electrons have fixed amounts of energy “quanta” Low energy  closer to nucleus High energy  further from nucleus

15. + Bohr Model

16. + Werner Heisenberg, 1927 It’s impossible to know both the location and the motion of an electron at the same time Heisenberg Uncertainty Principle

17. + Quantum Mechanical Model (aka wave mechanical model) Erwin Schrodinger – 1926 Electrons DO NOT orbit the nucleus Electrons DO have quanta of energy that determine placement in an atom

18. + Electron Cloud Area where there is a high probability that the electron will reside there 90% of the time

19. + Schrodinger’s Cat

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22. + Subatomic Particles

23. + Nucleus - protons - neutrons Electron Cloud - electrons + +o o --

24. + p + n 0 e - Found in the nucleus Mass = 1 (amu) Relative charge = +1 Found in the nucleus Same mass as a proton Mass = 1 amu Relative charge = 0 Found in the electron cloud around the nucleus Mass 1836 times smaller than a proton Therefore, mass doesn’t really count! (0.0005 amu) Relative charge = -1

25. + Atomic Number Atomic Number Z = p + the number of protons in the nucleus ALL atoms of the PROTONS SAME element have the IDENTIFY SAME atomic number and THE ELEMENT! SAME protons In a neutral atom, p + = e - Magnesium = Z = 12 12 protons 18.99

26. + Mass Number (nucleus!) Mass number = p + + n 0 (electrons don’t have much mass!!!) Z = 82  LEAD, Pb Mass 207 Protons? Electrons? Neutrons? 82 125 #n 0 = MN - # p + = 207 – 82 = 125 neutrons

27. + An element has an atomic number of 6 and a mass number of 14. What is the element? How many neutrons? Z = 6 CARBON MN = 14 #n = MN – #p + = 14 – 6 = 8 neutrons

28. + 1717 2 18.99 Average atomic mass (not the mass #) Period number (row) the number of energy levels outside of the nucleus Group number (column) the second digit tells us the number of valence (outer) electrons in a Bohr atom

29. + Bohr model of the atom Yep! Somebody lied when they told you 8! We’ll go into details in Unit 4. Hold your horses… (protons & neutrons)

30. + Identify this atom: (assuming it is neutral p + = e - ) NUCLEAR NOTATION 16 O 8 HYPHEN NOTATION Oxygen - 16

31. + If we drew a Bohr model of sodium: How many protons? How many neutrons? How many energy levels? How many electrons? 23 Na

32. + Scanning Electron Microscopes http://www.youtube.com/watch?v=egPQZw0QkVw