Chapter--3---Structure of the Atom

1. Chapter--3---Structure of the Atom

2. Men in Chemistry • Men in Chemistry: • Aristotle---matter is continuous in the universe • Democritus (400-300 B.C.)—matter is made of tiny particles ( proposed atoms) • Robert Millikan— (1905) • discovery of charge of e- • Mass of the e-

3. Men • John Dalton: • A) Law of Multiple Proportion---mass expressed in small whole numbers

4. Video: atoms

5. Men • B) Modern Atomic Theory ( 19th century) • 1) all matter is made of atoms • 2) all atoms of an element are identical • ( incorrect—differ in mass) • 3) atoms cannot be created, destroyed or divided • ( incorrect—can be split)

6. Men • 4) different atoms combine in simple whole # to form compounds • 5) chemical reactions do not break up atoms

7. Video: Dalton’s model

8. Men • J.J. Thomson- • Used Cathode ray tube to : • a) discover the e- b) determine the charge to mass ratio of e- c) proved that atoms could be divided

9. Men Cathode Ray Tube: page 80 Cathode—neg terminal Anode—pos terminal Cations (+) -collect at cathode Anions (-) collect at anode

10. Men • J.J. Thomson also proposed the “Plum Pudding Model” of the atom. • Compared atom to balls of pudding with fruit embedded.

11. Men • Ernest Rutherford—1911 • Gold Leaf Experiment--- • Alpha (+) particles were used to bombard a thin strip of gold foil. A fluorescent screen was used to show where alpha particles hit as they come through the foil. • This proved that the atom was mostly emptyspace.

12. Men • Rutherford— 1919 • Discovered the nucleus • He discovered the p+ in the center

13. Men • Nuclear Model— • The atom believed to have a tiny nucleus surrounded by lots of empty space for the e- to travel • If the diameter of the atom were to be the length of 2 football fields, the nucleus would be about the size of a nickel

14. Men • Neils Bohr—Planetary model of the atom • He believed the atom had a “+” center with e- revolving in orbits around it, somewhat like planets going around the sun • This was proved to be incorrect! • He also worked on Gold Leaf Experiment with Rutherford

15. Men Chadwick— • Working with Rutherford in 1932, determined that the nucleus had a neutral particle called the Neutron. • Neutron had a mass equal to the p+

16. Men • Subatomic Particles • Particle Charge Mass Location • P + 1 nucleus • N 0 1 nucleus • E - 0 outside nucleus

17. Men • Avogradro- • Avogradro’s Hypothesis—states that equal volumes of gases under the same conditions will have the same number of particles • 1 liter of CO2 will have the same number of molecules as a liter of O2 if they both are at the same pressure and temperature.

18. Men • Bacquerel— • discovered that Uranium was radioactive, by accidentally letting it expose photographic film

19. Men • Marie and Pierre Curie— • discovered radioactive Radium • did extensive work with radioactive • elements

20. Men • Mendelevee—First Periodic Law • He was first to see a periodic relationship among the elements. • He proposed that the properties of elements were a function of the atomic mass. ( incorrect)

21. Men • Henry Moseley– 1913- using x-rays he proposed the Modern Periodic Law— • state that properties of atoms are a function of the at # . The periodic table is arranged in order of increasing at #. • The at # is the same as the # of p+ in an atom

22. J.J. Berzelius developed the modern chemical symbol system • Three letters uun, unn etc

23. Men • Joseph Priestly— • discovered O • Lavoisier- • discovered H • concept of Law of Conservation of Mass

24. Men • Proust— • Law of Definite Proportions: • states that a specific substance always contains elements in the same ratio • Water always has 2 parts H and 1 part O

25. Men • Einstein--- • E = mc2 • E = energy • m = mass • c2 = speed of light in a vaccum

26. Uncertainty Principle: one can never be exactly sure of where the e- is because in order to see it , one must hit it with light and the light changes the momentum • Werner Heisenberg

27. The modern model of the atom is : • Quantum Mechanical Model • Max Planck: the quantum nature of energy

28. Louis de Broglie proved the “wave particle duality of nature”. A particle such as the e- can have the same properties as a wave. The physics is the same.

29. Atomic Structure • Mass of subatomic particles: • e- = .000549 ( too small to matter) • p+ = 1.0007276 • n = 1.0008665

30. Atomic structure • Atomic number---# of p+ in the atom ( small whole number on the chart) • Atomic mass----p+ + neutrons • atomic mass is all in the nucleus • # Electron = # proton ( neutral atom) • # neutrons = atomic mass - atomic #

31. Atomic structure • Fill in the chart: • Ele at.# at. mass p e n • K 19 39 19 19 20 • F 9 19 9 9 10\ • C • H

32. Atomic Structure • Isotopes----elements with the same atomic # but different atomic mass. ( same # of P + and e- but differ in # of neutrons) • Chemical behavior of isotopes is the same, because they have the same # of P+ and e-

33. Symbolic notation: • 12/6C pr 14/7N • At mass/at no. symbol • Hyphen notation: • C-12 or N-14

34. Ion: a charged particle • Neutral atom loses or gains an e- • Atom/ion e- p+ • Na ___ ___ • Na+ • Cl • Cl-

35. Atomic sturcture • All atoms have at least one isotope. The atomic mass of an atom is the AVERAGE OF ALL THE ISOTOPES OF ATOM • Ex: • Carbon 12 6p 6e 6n • Carbon 13 6p 6e 7n • Carbon 14 6p 6e 8n

36. Atomic Structure • Calculation of average mass: • Ave. mass = (% abundance)(mass) + (%abundance)( mass2) + ……. • Ex: Isotope “A” has an amu of 6.015 and %abundance is 7.5. Isotope “B” has an amu • of 7.016 and % abundance is 92.5%. • Page 105 old textbook # 33 and 34

37. Symbolic notation • Symbolic notation: • a fraction with atomic mass in numerator and atomic number in denominator to the left of the symbol for the element • 226/88Ra • 226 ----atomic mass • 88----atomic number

38. Atomic Structure • Carbon ---12-----chosen as the atomic mass standard. All amu ( atomic mass units) are a ratio of carbon 12.

39. Motion of the e- • Ground state ------lowest possible energy for the e- • Excited state-----high potential energy for e- ( far from nucleus)

40. Men • Page 91 # 3,5 • Page 97 7, 8,9 • Page 98 # 11,12,13 • Page 101 # 14 • Page -104 # 15,16,17 • Page 104 ---# 19,20,21