1. Nuclear Chemistry and Radioactivity
CHAPTER 20
Nuclear Chemistry and Radioactivity
20.2 Nuclear Reactions: Radioactivity

2. Nuclear reactions create new elements from other elements
electrons
protons
neutrons
Chemical reactions rearrange elements into new compounds, leaving the elements unchanged
Nuclear reactions create new elements from other elements
Nuclear equations
Chemical equations

3. A chemical reaction rearranges atoms to form new compounds:
4Fe(s) + 3O2(g) → 2Fe2O3(s)
rust

4. A chemical reaction rearranges atoms to form new compounds:
4Fe(s) + 3O2(g) → 2Fe2O3(s)
A nuclear reaction can
1) change one element into a new element:
2) change one isotope into another isotope of the same element:

5. Nuclear reactions
Nuclear reactions involve much more energy than chemical reactions
Nuclear reactions involve the strong nuclear force, the strongest force in the universe
A nuclear reaction can
1) change one element into a new element:
2) change one isotope into another isotope of the same element:

6. Nuclear reactions Decay reactions Fission reactions
There are two main types of nuclear reactions
Decay reactions
Alpha particle
A nucleus spontaneously disintegrates by emitting particles
Fission reactions
Note that the book refers to fission reactions as bombardment reactions
A nucleus is broken into two or more large pieces

7. Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay
Four most common types of nuclear decay:
Decay reactions
Alpha particle
A nucleus spontaneously disintegrates by emitting particles
1) Alpha (a) decay
2) Beta (b) decay
3) Gamma (g) decay
4) Positron (b+) emission

8. Isotopes that undergo spontaneous nuclear reactions are said to be radioactive.
Decay reactions
Alpha particle
A nucleus spontaneously disintegrates by emitting particles
radioactivity: a process by which the nucleus of an atom spontaneously changes itself by emitting particles or energy.

9. Intensity of radiation
Radiation can be dangerous because it has high enough energy to break bonds in molecules.
How do we measure the intensity of radiation?

10. Intensity of radiation
The farther we are from a source,
the the amount of radiation exposure.
smaller
larger

11. Intensity of radiation
The farther we are from a source,
the the amount of radiation exposure.
smaller
larger

12. intensity of radiation: the amount of energy that flows per unit area per time

13. Inverse square law: squared value
inverse square law: a law that states that the intensity of radiation emitted from a point source decreases inversely over the square of the distance.

14. Distance changes by a factor of 2
Inverse square law
Distance changes by a factor of 2
How does the intensity compare if you stand twice as far from a radiation source?

15. Distance changes by a factor of 2
Inverse square law
Distance changes by a factor of 2

16. Distance changes by a factor of 2
Inverse square law
Distance changes by a factor of 2
Intensity changes by a factor of 1/4 = 1/22

17. Inverse square law inverse square
When the distance changes by a factor of 2, the intensity changes by a factor of 1/22 = 1/4
When the distance changes by a factor of 10, the intensity changes by a factor of 1/102 = 1/100
inverse square

18. Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay
A nucleus spontaneously disintegrates
Four most common types of nuclear decay:
1) Alpha (a) decay
2) Beta (b) decay
3) Gamma (g) decay
4) Positron (b+) emission

19. Alpha decay Alpha decay: a nucleus emits a helium nucleus
Parent nuclide
Daughter nuclide
He-4 nucleus
(a particle)

20. Alpha decay
a particles are very large and cannot penetrate matter very well.
a particle
Remember Rutherford’s experiment: Most alpha particles went through the gold sheet. Nuclei in the gold sheet caused alpha particles to bounce off in new directions.

21. Alpha decay
a particles are very large and cannot penetrate matter very well.
a particle
Normally a particles cannot go through skin. However, if you eat something containing an a emitter, then the a particles can hit internal organs and cause damage.

22. Alpha decay
Write the complete nuclear equation for the a decay of the radium
isotope

23. Alpha decay
Write the complete nuclear equation for the a decay of the radium
isotope
Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to

24. Alpha decay
Write the complete nuclear equation for the a decay of the radium
isotope
Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to
Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 222. By balancing the atomic number, we obtain Z = 86.

25. Alpha decay
Write the complete nuclear equation for the a decay of the radium
isotope
Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to
Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 222. By balancing the atomic number, we obtain Z = 86. Second, look at the periodic table to determine the identity of the unknown daughter element. Since the atomic number is 86, the daughter nuclide is radon (Rn).

26. Alpha decay
Write the complete nuclear equation for the a decay of the radium
isotope
Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to
Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 222. By balancing the atomic number, we obtain Z = 86. Second, look at the periodic table to determine the identity of the unknown daughter element. Since the atomic number is 86, the daughter nuclide is radon (Rn).
Answer: The complete a decay equation is

27. Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay
A nucleus spontaneously disintegrates
Four most common types of nuclear decay:
1) Alpha (a) decay
2) Beta (b) decay
3) Gamma (g) decay
4) Positron (b+) emission

28. Beta decay
Beta decay: an unstable nucleus releases an electron and converts a neutron into a proton.
Parent nuclide
Daughter nuclide
b particle

29. Beta decay
Beta decay: an unstable nucleus releases an electron and converts a neutron into a proton.
Parent nuclide
Daughter nuclide
b particle
Charge goes from 0 to +1

30. Beta decay
Beta decay: an unstable nucleus releases an electron and converts a neutron into a proton.
Beta decay: an unstable nucleus releases an electron
Parent nuclide
Daughter nuclide
b particle
6 protons
7 protons
balanced equation

31. Alpha decay
Write the complete nuclear equation for the b decay of the radium
isotope

32. Alpha decay
Write the complete nuclear equation for the b decay of the radium
isotope
Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to

33. Alpha decay
Write the complete nuclear equation for the b decay of the radium
isotope
Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to
Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 228. By balancing the atomic number, we obtain 88 = Z – 1 or Z = 89.

34. Alpha decay
Write the complete nuclear equation for the b decay of the radium
isotope
Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to
Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 228. By balancing the atomic number, we obtain 88 = Z – 1 or Z = 89. Second, look at the periodic table to determine the identity of the unknown daughter element. Since the atomic number is 89, the daughter nuclide is actinium (Ac).

35. Alpha decay
Write the complete nuclear equation for the b decay of the radium
isotope
Relationships: We need to find the type of the daughter nucleus X, the atomic number Z, and the mass number A according to
Solve: First, balance the atomic number and the mass number. By balancing the mass number, we obtain A = 228. By balancing the atomic number, we obtain 88 = Z – 1 or Z = 89. Second, look at the periodic table to determine the identity of the unknown daughter element. Since the atomic number is 89, the daughter nuclide is actinium (Ac).
Answer: The complete a decay equation is

36. Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay
A nucleus spontaneously disintegrates
Four most common types of nuclear decay:
1) Alpha (a) decay
2) Beta (b) decay
3) Gamma (g) decay
4) Positron (b+) emission

37. Gamma decay
Gamma decay: a nucleus releases electromagnetic energy but the isotope remains the same.

38. Gamma decay
Gamma decay: a nucleus releases electromagnetic energy but the isotope remains the same.
Gamma radiation has high enough energy to break apart other atoms, but can be stopped by a thick shielding material made of lead or concrete.

39. Decay reactions Decay reactions 1) Alpha (a) decay 2) Beta (b) decay
A nucleus spontaneously disintegrates
Four most common types of nuclear decay:
1) Alpha (a) decay
2) Beta (b) decay
3) Gamma (g) decay
4) Positron (b+) emission

40. Positron emission
Positron emission: a nucleus releases a positron and converts a proton into a neutron.
A positron is a particle that has the same mass as an electron and has a positive charge

41. Determine the type of decay for the following reactions:

42. Determine the type of decay for the following reactions:
Asked: Unknowns X1 and X2
Given: Mass and atomic numbers of the parent and daughter nuclides.

43. Determine the type of decay for the following reactions:
Asked: Unknowns X1 and X2
Given: Mass and atomic numbers of the parent and daughter nuclides.
Solve: Balance the atomic numbers to find Z, and mass numbers to find A: For reaction 1: 234 = A1, so A1 = 0; 90 = 90 + Z1, so Z1 = 0.

44. Determine the type of decay for the following reactions:
Asked: Unknowns X1 and X2
Given: Mass and atomic numbers of the parent and daughter nuclides.
Solve: Balance the atomic numbers to find Z, and mass numbers to find A: For reaction 1: 234 = A1, so A1 = 0; 90 = 90 + Z1, so Z1 = 0. For reaction 2: 95 = 95 + A2, so A2 = 0; 43 = 42 + Z2, so Z2 = +1.

45. Determine the type of decay for the following reactions:
Asked: Unknowns X1 and X2
Given: Mass and atomic numbers of the parent and daughter nuclides.
Solve: Balance the atomic numbers to find Z, and mass numbers to find A: For reaction 1: 234 = A1, so A1 = 0; 90 = 90 + Z1, so Z1 = 0. For reaction 2: 95 = 95 + A2, so A2 = 0; 43 = 42 + Z2, so Z2 = +1.
Answer: For reaction 1, , which denotes g decay, so

46. Determine the type of decay for the following reactions:
Asked: Unknowns X1 and X2
Given: Mass and atomic numbers of the parent and daughter nuclides.
Solve: Balance the atomic numbers to find Z, and mass numbers to find A: For reaction 1: 234 = A1, so A1 = 0; 90 = 90 + Z1, so Z1 = 0. For reaction 2: 95 = 95 + A2, so A2 = 0; 43 = 42 + Z2, so Z2 = +1.
Answer: For reaction 1, , which denotes g decay, so
For reaction 2, , which denotes positron decay, so

47. There are two main types of nuclear reactions
Decay reactions
Alpha particle
A nucleus spontaneously disintegrates by emitting particles
Fission reactions
Note that the book refers to fission reactions as bombardment reactions
A nucleus is broken into two or more large pieces

48. Decay reactions a decay b decay g decay positron emission
A nucleus spontaneously disintegrates
b decay
g decay
positron emission