1. THE ULTIMATE IN SPONTANEITY
NUCLEAR CHEMISTRY
THE ULTIMATE IN SPONTANEITY

2. Review Atomic number (Z) – number of protons
Mass number (A) – sum of the protons and the neutrons
Isotopes or Nuclides– atoms with the same atomic number but different mass numbers, different numbers of neutrons.
Nucleons – the particles that make up the nucleus. (protons and neutrons = mass #)

3. Facts about the nucleus
Very small
Very dense
Held together by the nuclear strong force
Location of the protons and neutrons
Most of the mass of an atom is located

4. Mass Defect
You might expect the mass of an atom to be the same as the sum of it’s parts, protons, neutrons, and electrons.
Protons amu
Neutrons amu
Electrons amu

5. Mass Defect
The difference between the calculated mass and the actual mass is known as mass defect.

6. What causes the lost mass?
According to Albert Einstein, mass and energy can be converted into each other.
Some of the mass is lost during the formation of the nucleus.
The amount of energy can be calculated using Einstein’s famous equation.

7. Nuclear Binding Energy
The energy released when a nucleus is formed from nucleons.
E = mc2
E is for energy unit: Joules (J)=kg.m2/s2
M is for mass unit: kilograms (kg)
C is the speed of light (squared)
3.00 x 108 m/s

8. Binding Energy per Nucleon
The binding energy per nucleon is used to compare the stability of different nuclides.
It is the binding energy of the nucleus divided by the number of nucleons that are in the nucleus.

9. Binding Energy
The higher the binding energy per nucleon, the more tightly packed the nucleons are held together, the more stable the nuclide.
"A is for atom" (1952) video

10. Binding Energy
Elements with intermediate atomic masses have the greatest binding energies per nucleon and are therefore the most stable. Iron is the most stable isotope.

11. Binding Energy per Nucleon

12. How does the nucleus stay together?
Relationship between the nuclear strong force and the electrostatic forces between protons.
Like charges repel each other through electrostatic repulsion

13. How does the nucleus stay together?
The nuclear strong force allows protons to attract each other at very short distances.
As protons increase in the nucleus so does the electrostatic forces, faster than nuclear forces.

14. Why do atoms want more neutrons than protons?
More neutrons are required to increase the nuclear force and stabilize the nucleus.
> 83 the repulsive forces of protons is so great that no stable nuclides exist.

15. Band of Stability Stable nuclides have certain characteristics
When the number of neutrons are plotted against the number of protons a pattern is observed

16. Band of Stability
The neutron-proton ratio of stable isotopes cluster around a narrow band called the band of stability.
For atoms with low atomic numbers the ratio is 1 : 1
As the atomic number increases, the ratio increases to 1.5 : 1

17. Band of Stability

18. Magic Numbers Stable nuclides tend to have even numbers of nucleons.
159 have both even protons and neutrons
Only 4 have odd numbers of protons and neutrons.

19. Nuclear Shell Model
Nucleons exist in different energy levels, or shells, in the nucleus.
The number of nucleons that represent completed nuclear energy levels,
2, 8, 20, 28, 50, 82, and 126
Called magic numbers

20. Nuclear Reactions
Unstable nuclei undergo spontaneous changes that change the number of protons and/or neutrons.
Give off large amount of energy by emitting radiation during the process of radioactive decay.

21. Nuclear Reactions
Eventually unstable radioisotopes of one element are transformed into stable, non-radioactive, isotopes of a different element.
Total of mass number and atomic number must be equal on both sides of a reaction.

22. Nuclear Reactions
When the atomic number changes, the identity of the element changes.
A transmutation is a change in the identity of a nucleus as a result of a change in the number of protons.

23. Nuclear Reactions C  e + N
Mass Number’s must equal on both sides of the equation.
C  e N
Atomic number’s must equal on both sides of the equation

24. Nuclear Reactions
Try one!
U  He +
_______

25. Nuclear Reactions
Try one!
U  He Th

26. Types of Radiation Alpha Radiation
Alpha radiation is a heavy, very short-range particle and is actually an ejected helium nucleus stripped of it’s electrons

27. Alpha Radiation 2 protons and 2 neutrons.
Charge +2 (lost both electrons)
Large mass, 4 amu.
Low penetration power
Shielded by paper or clothing.

28. Alpha Radiation
Occurs in unstable nuclei that has too many protons and too many neutrons.
Effect on the nucleus:
Mass number is reduced by 4 amu
Atomic number is reduced by 2

29. Beta Radiation A fast moving electron
Occurs in an unstable nuclei that has too many neutrons

30. Beta Radiation Converts a neutron into a proton and a beta particle
An electron that doesn’t belong in the nucleus and therefore gets thrown out.

31. Beta radiation Charge -1 Mass = 1/1840 or 0.0005486 amu
Moderate penetration power (0.4 cm)
Shielded by metal foil
Effect on nucleus:
Mass number remains the same
Atomic number increases by 1

32. Positron emission A positive electron
Has the same mass as an electron, 1/1840 or amu

33. Positron emission Charge +1
Occurs in unstable nuclei that has too many protons
Converts a proton into a neutron
Effect on the nucleus:
Mass number remains the same
Atomic number decreases by 1

34. Electron Capture
Occurs in unstable nuclei that has too many protons: same as positron emission
An inner orbiting electron gets captured by the nucleus and is used to convert a proton into a neutron.

35. Electron Capture The effect is the same as for positron emission
Mass number remains the same
Atomic number decreases by 1

36. Gamma radiation Is high-energy electromagnetic radiation
No charge and no mass: no effect on the nucleus
Penetration power is high and only lead and several centimeters of concrete can slow it down
Always accompanies another form of radiation

37. Half-Life No two radioisotopes decay at the same rate.
t1/2 is the symbol for half-life
Half-life is the time required for half the atoms of a radioactive nuclide to decay.
The longer the half-life the more stable the nuclide.

38. Half-life Variables Variables Ao = original amount A = final amount
T = total time elapsed
t1/2 = half-life
n = number of half-lives

39. Half-life Equations
n = T
t1/2
Ao = A * 2n

40. Half-life Calculations
To solve half-life problems first write down all of the data in the problem.
Determine which formula you’re going to use.
Plug in the values and calculate

41. Half-life problem
Phosphorus-32 has a half-life of 14.3 days. How many milligrams of phosphorus-32 remains after 57.2 days if you start with 4.0 mg of the isotope?
A0 = 4.0 mg A = ?
T = 57.2 days n = T / t1/2
t1/2 = 14.3 days A = A0 / 2n

42. Problem (Con’t) n = T / t1/2 n = 57.2 days / 14.3 days
n = 4 half-lives
A = A0 / 2n
A = 4.0 mg / 24
A = 4.0 mg / 16
A = 0.25 mg

43. Half-life graphic Picture representation of half-life ½ remain ½ decay

44. Total time problem
The half-life of radon-222 is days. After what time will one-fourth of a given amount of radon remain?
A = ¼ remain n = T / t1/2
T = ?
t1/2 = days

45. Total time problem (Con’t)
* We don’t need to know the beginning amount. Looking at the picture representation we see that it needs to go through 2 half-lives in order to have ¼ remaining.
n = T / t1/2
2 = T / days
T = 2 x days
T = days

46. Decay Series
One nuclear reaction is not always enough to produce a stable nuclide.
A decay series is a series of radioactive nuclides produced by successive radioactive decay until a stable nuclide is reached.

47. Decay Series
The heaviest nuclide of each decay series is the parent nuclide and the nuclides produced by the decay is called the daughter nuclide.

48. Artificial Transmutations
Artificial radioactive nuclides are radioactive nuclides not found naturally on Earth.
They are made by artificial transmutations, bombardment of nuclei with charged and uncharged particles.

49. Artificial Transmutations
Neutrons have no charge and no mass and can easily penetrate the nucleus of an atom.
Positively charged alpha particles, protons, and other ions are repelled by the nucleus.

50. Artificial Radioactive Nuclides
A great deal of energy is needed to bombard nuclei with these particles.
Energy may be supplied by accelerating these particles in the magnetic or electric field of a particle accelerator.
Radioactive isotopes of all the natural elements have been produced.

51. Artificial Radioactive Nuclides
Technetium and Promethium are not natural elements and have been artificially produced and have filled gaps in the periodic table.
Transuranium elements are elements with more than 92 protons in their nucleus.
All are radioactive and man-made.

52. Nuclear Radiation
Nuclear Radiation can transfer energy form nuclear decay to the electrons of atoms or molecules and cause ionization.
A roentgen (R) is a unit used to measure nuclear radiation exposure.
A rem (roentgen equivalent, man) is a unit used to measure the dose of any type of ionizing radiation that factors in the effect that the radiation has on human tissue.

53. Nuclear Exposure
Long term exposure to radiation can cause DNA mutations that result in cancer and other genetic defects.
Average background radiation exposure in the U.S. is ~0.1 rem per year.
The maximum permissible dose of radiation exposure for a person in the general population is 0.5 rem/year.

54. Radiation Detection
Film badges use exposure of film to measure the approximate radiation exposure of people working with radiation.
Geiger-Muller Counters are instruments that detect radiation by counting electric pulses carried by gas ionized by radiation.
Used to detect beta, x-rays, and gamma radiation

55. Radiation Detection
Radiation can also be detected when it transfers its energy to substances that scintillate, or absorb ionizing radiation and emit visible light.
Scintillation counters are instruments that convert scintillations light to an electric signal for detecting radiation.

56. Nuclear Fission
A very heavy nucleus splits into more-stable nuclei of intermediate mass.
Releases enormous amounts of energy
Occurs spontaneously or when bombarded by particles.
Nuclear Fission video
"A is for Atom" part 2

57. Manhattan Project videos
Part 1 of 5
Part 2 of 5
Part 3 of 5
Part 4 of 5
Part 5 of 5

58. Nuclear Chain Reactions
A chain reaction is a reaction in which the material that starts the reaction is also one of the products and can start another reaction.
When there isn’t enough starting material left or when the neutrons escape without hitting the nucleus, the reaction stops.
A critical mass is needed to sustain the chain reaction.
The minimum amount of nuclide that provides the number of neutrons needed to sustain a chain reaction.

59. Nuclear Reactors
Use controlled-fission chain reactions to produce energy and radioactive nuclides.
Nuclear power plants convert heat produced by nuclear fission into electrical energy.

60. Nuclear power plants
There are five main components: sheilding, fuel, control rods, moderator, and coolant.
Shielding – radiation-absorbing material used to decrease the emission of radiation, especially gamma rays, from nuclear reactors.
Control rods – neutron-absorbing rods that help control the reaction by limiting free neutrons.
Moderator – used to slow down the fast neutrons produced by fission
Uranium-235 is usually the fuel
Coolant is simply water which can absorb neutrons to become heavy water, the H2O becomes D2O.

61. Nuclear Fusion
Low-mass nuclei combine to form a heavier, more stable nucleus.
Releases more energy per gram of fuel than fission.
Occurs at extremely high temperature and pressure.
Occurs in our sun and stars that are similar to our sun.
Researchers are currently studying ways to contain the reacting plasma that is required for fusion.

62. Nuclear Fusion videos
Tayor Willson "Yup I built a nuclear fusion reactor”
"How nuclear fusion works"