1. Unit 4- Atomic Theories and Nuclear Chemistry
Chapters
3 & 22

2. Kishan Alluri Christina Costeas Sandy Jiang Patrick Morgan Ben Wong
J.J. Thomson
Kishan Alluri
Christina Costeas
Sandy Jiang
Patrick Morgan
Ben Wong

3. Cathode Ray Experiment
zbT8

4. Background Born in Manchester, England in December 1856
Studied physics and mathematics
Won a nobel prize in 1906

5. Experiment Observations (on page 71)
An object placed between the cathode and the opposite end of the tube cast a shadow on the glass.
A paddle wheel placed on rails between the electrodes rolled along the rails from the cathode toward the anode.
Cathode rays were deflected by a magnetic field in the same manner as a wire carrying electric current, which was known to have a negative charge.
The rays were deflected away from a negatively charged object.

6. Discovery of Electrons-1897
Experiments supported hypothesis that the particles that compose cathode rays are negatively charged
Measured the ratio of cathode-ray particles to their mass—found it was always the same
Concluded that all cathode rays are composed of identical negatively charged particles called electrons
Experiments revealed the electron has a very large charge for its tiny mass

7. Robert Millikan By: Katrina Leung, Jesse Stathis, Jenna Taormina,
Danielle Zhang, Matt Odea

8. Millikan’s Atomic Theory
Electrons are really small
Mass of electron 1/2000 the mass of a hydrogen atom
Electron has a mass of * 10^-31kg or 1/1837 the mass of a hydrogen atom
Electrons carry a negative charge

9. Video on Millikan’s Oil Experiment

10. New Inferences about Atomic Structure
Because atoms are electrically neutral, they must contain a positive charge to balance the negative electrons.
Because electrons have so much less mass than atoms, atoms must contain other particles that account for most of their mass.

11. Lord Rutherford of Nelson
As flawlessly explained by: Adam, Jane, Justin, Jeremy,
rob

12. Rutherfordian History
Born 1871 in New Zealand
In early work, discovered radioactive half-life
Had an element named after him- rutherfordium
Became known as the father of nuclear physics

13. Discovery of the Atomic Nucleus
Assistants Geiger and Marsden bombarded a thin piece of gold foil
with a narrow beam of alpha particles.
Some of the particles were redirected by the gold foil back towards their source.
Rutherford thus concluded that the force must be caused by a very densely packed bundle of matter with a positive charge, which he called the nucleus.

14. The Experiment
Rutherford had discovered that the volume of the nucleus was very small compared to the total volume of the atom, suggesting that there was a lot of empty space.

15. By Monica, Santosh, Jennie, Antonella, and Drew
James Chadwick
By Monica, Santosh, Jennie, Antonella, and
Drew

16. James Chadwick’s Discovery of the Neutron
In 1932, Chadwick discovered a previously unknown particle in the atomic nucleus.3 This particle became known as the neutron because of its lack of electric charge. Chadwick's discovery was crucial for the fission of uranium 235.

17. A. Mass Number always a whole number NOT on the Periodic Table!
mass # = protons + neutrons
© Addison-Wesley Publishing Company, Inc.
always a whole number
NOT on the Periodic Table!

18. Mass # Atomic # B. Isotopes Nuclear symbol: Hyphen notation: carbon-12
Atoms of the same element with different mass numbers.
Nuclear symbol:
Mass #
Atomic #
Hyphen notation: carbon-12

19. B. Isotopes
© Addison-Wesley Publishing Company, Inc.

20. B. Isotopes Chlorine-37 atomic #: 17 mass #: 37 # of protons:17
# of electrons:17
# of neutrons:20

21. B. Isotopes Chlorine-35 atomic #: 17 mass #: 35 # of protons:17
# of electrons:17
# of neutrons:18

22. C. Relative Atomic Mass atomic mass unit (amu)
12C atom = × g
atomic mass unit (amu)
1 amu = 1/12 the mass of a 12C atom
1 p = amu 1 n = amu 1 e- = amu
© Addison-Wesley Publishing Company, Inc.
C. Johannesson

23. D. Average Atomic Mass Avg. Atomic Mass
weighted average of all isotopes
on the Periodic Table
round to 2 decimal places
Avg.
Atomic
Mass

24. D. Average Atomic Mass Avg. Atomic 16.00 Mass amu
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
Avg.
Atomic
Mass
16.00
amu

25. D. Average Atomic Mass 35.40 amu Avg. Atomic Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Avg.
Atomic
Mass
35.40 amu

26. New Terms for Nuclear Chemistry
Atom = nuclide
Nucleus = nucleon

27. A. Mass Defect
Difference between the mass of an atom and the mass of its individual particles.
amu
amu

28. Mass of subatomic particles:
Protons u
Electrons – u
Neutrons – u
Ex. Helium-4 has an atomic mass of
Calculate the mass defect:
2 Protons = (2x )= u
2 Electrons = (2x ) = u
2 Neutrons = (2x )= u
Total = u
Mass defect = =

29. What causes the loss of mass?
It is nuclear binding: (Energy released when a nucleus is formed from nucleons)
According to E=mc2:
Mass can be converted into energy and energy to mass
The mass defect is caused by the conversion of mass to energy upon formation of the nucleus.

30. Calculating the Binding Energy:
E=mc2
E-energy (J, Joules)
m- mass (kg)
c- speed of light (3.00x108 m/s)
J= kg x m2 s2
Steps:
Calculate the mass defect in (u).
Convert to kg using 1u=1.6605X10-27kg
Plug in to energy equation

31. Practice:
1. Calculate the binding energy of Sulfur-32. The measured atomic mass is u.
(4.36 x J)
2. Calculate the nuclear binding energy per mole of Oxygen-16. The measured atomic mass of oxygen is u.
(1.23 x 1013 J)
3. Calculate the binding energy per nucleon of a Manganese-55 atom. It’s measured atomic mass is u.
(1.41 x 10-12J)

32. B. Nuclear Binding Energy
Energy released when a nucleus is formed from nucleons.
High binding energy = stable nucleus.
E = mc2
E: energy (J)
m: mass defect (kg)
c: speed of light (3.00×108 m/s)

33. Do now:
Calculate the binding energies of the following two nuclei, and indicate which nucleus releases more energy when formed.
A. Potassium–35, Atomic mass
B. Sodium – 23, Atomic Mass

34. Do now: Potassium–35, Atomic mass 34.988011
4.47 X J
B. Sodium – 23, Atomic Mass
2.99 x J
Potassium releases more energy

35. B. Nuclear Binding Energy
Unstable nuclides are radioactive and undergo radioactive decay.

36. Binding energy per nucleon
Binding energy per nucleon, is the binding energy of the nucleus divided by its number of nucleons.
The higher the binding energy per nucleon, the more tightly the nucleons are held together.
Elements with intermediate atomic masses have the greatest binding energies per nucleon and are therefore the most stable.

37. The Band of Stability
What observations can you make?

38. Band of Stability
Atoms having low atomic numbers, are the most stable.
N:P = 1:1
As atomic number increases the N:P increases (1.5:1)

39. Band of Stability Why does this happen?
- Explained by the relationship btwn nuclear force and electrostatic forces btwn protons.
Protons in the nucleus repel all other protons through electrostatic repulsion.
As #p increase, the repulsive electrostatic force between protons increase faster than the nuclear force
More neutrons are required to increase the nuclear force to stabilize the nucleus.

40. Band of Stability
Beyond Bismuth (#83), the repulsive forces of protons are so great that no stable nuclide exists.
Stable nuclei tend to have even number of nucleons

41. A. Types of Radiation Alpha particle () helium nucleus
2 protons and 2 neutrons bound together and emitted from the nucleus
Restricted nearly to heavy atomic nuclei
Mostly because protons numbers need to be reduced to stabilize the nuclei

42. A. Types of Radiation Beta (-)
Is an electron emitted from the nucleus during some kinds of radioactive decay.
Usually for the nuclides above the band of stability, to decrease the number of neutrons.
Electron is emitted from the nucleus as a beta particle.

43. A. Types of Radiation Positron particle (+)
Particle has the same mass as an electron but has a positive charge and emitted from the nucleus
Proton is converted into a neutron

44. A. Types of Radiation 2+ 1- 1+ Beta particle (-) electron
Alpha particle ()
helium nucleus
Beta particle (-)
electron 1-
Positron (+)
positron 1+
Gamma ()
high-energy photon

45. B. Nuclear Decay Numbers must balance!! parent nuclide daughter
Alpha Emission
parent
nuclide
daughter
nuclide
alpha
particle
Numbers must balance!!

46. B. Nuclear Decay
Beta Emission
electron
Positron Emission
positron

47. B. Nuclear Decay electron Gamma Emission
Electron Capture
electron
Gamma Emission
Usually follows other types of decay.
Transmutation
One element becomes another.

48. Complete the following:

49. Complete the following:

50. Complete the following:

51. Complete the following:

52. Complete the following:

53. B. Nuclear Decay Why nuclides decay…
need stable ratio of neutrons to protons
DECAY SERIES TRANSPARENCY

54. Characteristics of stable nuclei:
When number of protons is plotted against number of neutrons, a belt-like graph is obtained.
Atoms of low atomic numbers have stable nuclei with a ratio of 1:1, p:n
As atomic number increases, the p:n increases

55. What happens when p:n increase?
Explained by nuclear and electrostatic forces between protons.
Protons in the nucleus repel each other bc of electrostatic repulsion
However Nuclear forces allow protons to attract to other protons in close proximity
As #p increase the repulsive electrostatic force between protons increase faster than the nuclear force. Therefore creating an unstable nucleus.
More neutrons are required to stabilize this force.

56. Radioactive Decay
The spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by the emission of particles, electromagnetic radiation or both.
Leads to more stable nucleons.

57. C. Half-life Half-life (t½)
Time required for half the atoms of a radioactive nuclide to decay.
Shorter half-life = less stable.

58. mf: final mass mi: initial mass n: # of half-lives
C. Half-life
mf: final mass
mi: initial mass
n: # of half-lives
n: t/T t = time elapsed
T = Length of half life

59. C. Half-life t½ = 5.0 s mf = mi (½)n mi = 25 g mf = (25 g)(0.5)12
Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s?
GIVEN:
t½ = 5.0 s
mi = 25 g
mf = ?
total time = 60.0 s
n = 60.0s ÷ 5.0s =12
WORK:
mf = mi (½)n
mf = (25 g)(0.5)12
mf = g

60. Add in new equation

61. More Half-life problems: (wkst)
The half-life of carbon-14 is 5715 years. How long will it be until only half of the carbon-14 in a sample remains? (5715y)
The EPA is concerned about the levels of radon gas in homes. The half-life of radon- 222 isotope is 3.8days. If a sample of gas taken from a basement contained 4.38ug of radon-222, how much will remain after days? (0.274ug)
Uranium-238 decays through alpha decay with a half life of 4.46x109years. How long would it take for 7/8 of a sample of uranium- 238 to decay? (three half-lives or 1.34 x 1010 years)

62. Decay Series Parent Nuclide: The heaviest nuclide of each decay series
Daughter Nuclide:
The nuclide produced by decay of the parent nuclide

63. A. F ission splitting a nucleus into two or more smaller nuclei
1 g of 235U = 3 tons of coal

64. A. F ission chain reaction - self-propagating reaction
critical mass - mass required to sustain a chain reaction

65. B. Fusion combining of two nuclei to form one nucleus of larger mass
thermonuclear reaction – requires temp of 40,000,000 K to sustain
1 g of fusion fuel = 20 tons of coal
occurs naturally in stars

66. C. Fission vs. Fusion 235U is limited fuel is abundant
danger of meltdown
toxic waste
thermal pollution
fuel is abundant
no danger of meltdown
no toxic waste
not yet sustainable

67. A. Nuclear Power
Fission Reactors
Cooling Tower

68. A. Nuclear Power
Fission Reactors

69. A. Nuclear Power
Fusion Reactors (not yet sustainable)

70. A. Nuclear Power Fusion Reactors (not yet sustainable)
National Spherical Torus Experiment
Tokamak Fusion Test Reactor
Princeton University

71. B. Synthetic Elements Transuranium Elements
elements with atomic #s above 92
synthetically produced in nuclear reactors and accelerators
most decay very rapidly

72. C. Radioactive Dating
half-life measurements of radioactive elements are used to determine the age of an object
decay rate indicates amount of radioactive material
EX: 14C - up to 40,000 years 238U and 40K - over 300,000 years

73. Radiation treatment using
D. Nuclear Medicine
Radioisotope Tracers
absorbed by specific organs and used to diagnose diseases
Radiation Treatment
larger doses are used to kill cancerous cells in targeted organs
internal or external radiation source
Radiation treatment using
-rays from cobalt-60.

74. E. Nuclear Weapons Atomic Bomb Hydrogen Bomb
chemical explosion is used to form a critical mass of 235U or 239Pu
fission develops into an uncontrolled chain reaction
Hydrogen Bomb
chemical explosion  fission  fusion
fusion increases the fission rate
more powerful than the atomic bomb

75. F. Others Food Irradiation Radioactive Tracers Consumer Products
 radiation is used to kill bacteria
Radioactive Tracers
explore chemical pathways
trace water flow
study plant growth, photosynthesis
Consumer Products
ionizing smoke detectors - 241Am