1. Nuclear Chemistry
Chapter 25

2. Changes in the Nucleus
Nuclear reactions – reactions that change the composition of an atom’s nucleus
Strong Force – attractive force that overcomes electromagnetic repulsion in the nucleus of an atom

3. Changes in the Nucleus
Nuclear reactions produce three kinds of radiation:
Alpha
Beta
Gamma

4. Penetrating Distances

5. Changes in the Nucleus 1. Alpha radiation – helium-4 nucleus
- Heavy particle with not that much penetrating power
- Paper and clothing protect you

6. Changes in the Nucleus 2. Beta radiation – an electron
– more penetrating
– 1 to 2 mm into solid material
3. Gamma radiation – non-particulate radiation
– very penetrating form of electromagnetic radiation

7. Table O

8. Nuclear Chemistry
Transmutation – changing the nucleus of an atom into the nucleus of a different atom

9. Nuclear Stability PROTONS have two forces acting on them
Electrostatic force of repulsion
Strong nuclear force of attraction

10. Nuclear Stability NEUTRONS have one force acting on them
Only a Strong nuclear force
Neutrons add a net attractive force to the inside of the nucleus

11. Nuclear Stability PROTON to NEUTRON RATIO
For elements 1-20, there are approximately equal numbers of protons and neutrons in the nucleus
Beyond element 20 there needs to be increasingly more neutrons than protons to stabilize the nucleus

12. Nuclear Stability (P to N Ration)
When the number of protons exceeds 83 (bismuth), no number of neutrons can stabilize the nucleus – all atoms with atomic numbers greater than 83 are Radioactive.

13. Nuclear Chemistry
The stability of the nucleus of an atom is determined by the ratio of protons to neutrons.

14. Unstable
Nuclei that have too many or too few neutrons (heavy isotopes) are also unstable and tend to be radioactive and emit radiation.

15. Nuclear Chemistry
An unstable nucleus will spontaneously decay, it emits radiation in forming more stable products:
1. alpha particle – helium nucleus, 2 protons and 2 neutrons
2. beta particle – an electron whose source is an atomic nucleus
3. positron – a positively charged electron
4. gamma rays – form of energy released from nuclear decay

16. Table O

17. Nuclear Chemistry Radiation is harmful to living things
ionizes molecules in cells
can cause mutations in DNA

18. Alpha decay

19. Nuclear Decay
Alpha Decay:
Ra ―› He
222
+ Rn 86

20. Beta Decay
n ―› p e
the number of protons increases by 1
the atomic number increases by 1
the number of neutrons decreases by 1
the mass number remains the same

21. Beta Decay
Write the nuclear equation for the beta decay of lead – 214
214
Pb ―› 82 e -1
214
+ Bi 83

22. Beta Decay

23. Nuclear Decay
Positron Emission – the production of a positron when a proton is converted to a neutron
p ―› n e
The number of protons decreases by 1
The atomic number decreases by 1
The number of neutrons increases by 1
The mass number stays the same

24. Positron Decay/Emission

25. Positron Decay K ―› 19 37 e + Ar +1 18
Write the nuclear equation for the positron decay of potassium - 37 37
K ―› 19 e +1 37 Ar 18

26. Complete the Following Nuclear Equations
Beta Decay
14 14
C ―› N X
Th ―› Ra X e -1
According to Table O
What kind of decay is occurring in each? 4 He 2
Alpha Decay

27. Complete the Following Nuclear Equations
Alpha Decay
X ―› Pb He
U n ―› Np X
212 Po 84
Beta Decay e -1

28. Transmutation
Transmutation - changing the nucleus of an atom into the nucleus of a different atom
2 types
Natural Transmutation
Artificial Transmutation

29. Artificial Transmutation – bombarding a nucleus with high–energy particles to bring about change
Protons or alpha particles are accelerated in magnetic fields
Neutrons are collided with nuclei – this is done in nuclear reactors

30. Nuclear Decay Natural Artificial 212 208 4 Po ―› Pb + He 84 82 2
Natural transmutation has one reactant, artificial transmutation has two reactants
Po ―› Pb He
U n ―› Np e
Natural
Artificial

31. Nuclear Fission
Fission – splitting heavy nuclei to make lighter nuclei
E = mc2
The energy from the amount of mass converted to energy in nuclear reactions – this mass is called the mass defect

32. Nuclear Fission 142 91 1 1 235 Ba + Kr + 3 n + energy n + U ―› 56 36 0
Ba Kr n + energy
n U ―›

34. Nuclear Fusion Fusion – combining light nuclei to make heavier nuclei
requires very high temperature and pressure
energy source of the sun
products of fusion not highly radioactive

35. Nuclear Fusion
H H ―› 1 4
He energy 2

36. In fission and fusion reactions, there appears to be a loss of mass.
However, this mass has been converted to energy by the equation
E = mc2

37. Nuclear Weapons
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion.
Both reactions release vast quantities of energy from relatively small amounts of matter.

38. Which reaction would you rather see?
Chemical Reaction
Nuclear Reaction

40. Measuring Nuclear Decay
Half-Life - the time it takes for ½ of the atoms in a given sample to decay
40 g of a substance with a half life of 10 s begins to decay:
20 g after 10 s
10 g after 20 s
5 g after 30 s

41. Measuring Nuclear Decay
fraction remaining = (1/2)n
n = # of half-lifes

42. Measuring Nuclear Decay
A 52.0 g sample of Cr – 51 has a half-life of 28 days
What fraction of the sample will remain after 168 days?