1. Chapter 10 Nuclear Chemistry
Section Radioactivity
Section Fission and Fusion

2. Section 10.1 Radioactivity
Nuclear Decay
Antoine Henri Becqueral ( )-discovery of radioactivity
Radioactivity-the process in which an unstable atomic nucleus emits charged particles and energy
Any atom containing an unstable nucleus is a radioactive isotope aka. radioisotope

3. Section 10.1 Radioactivity
Nuclear Decay
Becquerel-used uranium-238 in his experiment
Radioisotopes spontaneously change into other isotopes over time.
When composition of a radioisotope changes=undergoes nuclear decay
Key Concept: During nuclear decay, atoms of one element can change into atoms of a different element altogether.

4. Section 10.1 Radioactivity
Types of Nuclear Radiation
Radioactive substances can be detected by measuring the nuclear radiation they give off.
Nuclear radiation-charged particles and energy that are emitted from the nuclei of radioisotopes
Key Concept: Common types of nuclear radiation include alpha particles, beta particles, and gamma rays.

5. Section 10.1 Radioactivity
Types of Nuclear Radiation: Alpha Decay
Uranium-238 decays=emits alpha particles
Def.-a positively charged particle made up of two protons and two neutrons (the same as a helium nucleus)
Symbol for alpha particle 4/2 He; subscript(2) is the atomic number; superscript(4) is the mass number (#protons + #neutrons)
Also notated by Greek letter α

6. Section 10.1 Radioactivity
Types of Nuclear Radiation: Alpha Decay
Refers to nuclear decay that releases alpha particles
Is an example of a nuclear reaction
Nuclear reactions can be expressed as equations.
238/92 U → 234/90 Th + 4/2 He
Alpha decay: product isotope has two fewer protons and two fewer neutrons than the reactant isotope
Alpha particles: least penetrating and only travel a few centimeters in the air

7. Section 10.1 Radioactivity
Types of Nuclear Radiation: Beta Decay
Thorium-234 decays=releases negatively charged radiation (beta particles)
Def.-an electron emitted by an unstable nucleus
Nuclear equations written: 0/-1 e or β
Atomic number is -1 because of negative charge
Very little mass (1/1836)=mass number is 0

8. Section 10.1 Radioactivity
Types of Nuclear Radiation: Beta Decay
How can an atom’s nucleus, which is positively charged, emit a negatively charged particle?
A neutron decomposes into a proton and an electron.
The proton stays trapped in the nucleus; the electron is released
234/90 Th → 234/91 Pa + 0/-1 e
The product isotope has 1 proton more and 1 neutron fewer than the reactant isotope.
Mass numbers of isotopes are the same b/c the beta particle emitted basically has no mass.
Beta particles: smaller mass, move at faster speed and penetrate more than alpha particles

9. Section 10.1 Radioactivity
Types of Nuclear Radiation: Gamma Decay
Nuclear radiation does not always consist of charged particles.
Gamma ray-a penetrating ray of energy emitted by an unstable nucleus
Gamma radiation: has no charge and no mass
**Travel through space at the speed of light

10. Section 10.1 Radioactivity
Types of Nuclear Radiation: Gamma Decay
Gamma Decay: the atomic number and mass number of the atom remain the same
**The energy of the nucleus decreases
Often accompanies alpha or beta decay.
Abbreviated: γ
Much more penetrating than alpha or beta particles
Takes several centimeters of lead or meters of concrete to stop gamma radiation

11. Penetrating Powers of Nuclear Radiation
Figure 4

12. Section 10.1

13. Section 10.1 Radioactivity
Effects of Nuclear Radiation
We are exposed to nuclear radiation daily.
Background radiation-nuclear radiation that occurs naturally in the environment
Radioisotopes in air, water, rocks, plants and animals contribute to background radiation.
Cosmic rays (streams of charged particles) from outer space
Background radiation levels, in general, are low enough to be safe.

14. Section 10.1 Radioactivity
Effects of Nuclear Radiation
Nuclear radiation goes over background levels=damage cells and tissues of the body
Key Concept: Nuclear radiation can ionize atoms.
Cells exposed=bonds holding DNA molecules and proteins together may break=cells may not function properly
Alpha particles, Beta particles and Gamma rays are all forms of ionizing radiation.

15. Section 10.1 Radioactivity
Effects of Nuclear Radiation
Alpha particles-skin damage similar to a burn; not serious hazard unless the substance emitting the particles is inhaled or eaten
Beta particles-damages tissues in the body more than alpha particles
Gamma rays-can penetrate deeply into the human body; all organs can be exposed to ionization damage

16. Section 10.1 Radioactivity
Detecting Nuclear Radiation
Scientific instruments can measure nuclear radiation.
Key Concept: Devices that are used to detect nuclear radiation include Geiger counters and film badges.
Geiger counter-uses gas-filled tube to measure ionizing radiation
Nuclear radiation enter the tube, ionizes atoms of the gas, ions produce an electric current (measured)
>the amount of nuclear radiation, the >the electric current produced in the tube

17. Section 10.1 Radioactivity
Detecting Nuclear Radiation
People working near or with radioactive materials wear film badges to monitor their exposure to nuclear radiation.
Film badge-piece of photographic film wrapped in paper
Film is developed and replaced with a new one periodically
Exposure on film shows the amount of radiation the person wearing badge was exposed to

18. Section 10.4 Fission and Fusion
Alternative energy sources may eventually take the place of fossil fuels (oil and coal)
Nuclear energy is one that is widely used today.
After discovery of radioactivity, found that atomic nuclei have vast amounts of energy
Transmutations involved more than just the conversion of one element into another; they also involved conversion of mass into energy.
Transmutation-conversion of atoms of one element to atoms of another (Section 10.3)

19. Section 10.4 Fission and Fusion
Nuclear Forces
What holds the nucleus of an atom together?
Strong nuclear force-the attractive force that bind protons and neutrons together in the nucleus
Does not depend on charge: acts among protons, among neutrons, and both protons and neutrons
Key Concept: Over very short distances, the strong nuclear force is much greater than the electric forces among protons.
Weakens as protons and neutrons get farther apart.

20. Section 10.4 Fission and Fusion
The Effect of Size on Nuclear Force
Effect of size of the nucleus on the force is complicated.
More protons and neutrons=more possibilities there are for strong nuclear force attractions
As size of nucleus increases, distance between protons and neutrons increases
**Strong nuclear forces act over short distances=possibilities of many attractions is not realized in a large nucleus
Nuclear force felt by proton and neutron in a large nucleus is about the same as the force felt in a small nucleus

21. Section 10.4 Fission and Fusion
Unstable Nuclei
Nucleus becomes unstable (ie. Radioactive) when the strong nuclear force can no longer overcome the repulsive electric forces among protons
Electric forces increase as nucleus size increases.

22. Section 10.4 Fission and Fusion
Hahn and Strassman (German chemists) 1938
Series of transmutation experiments (conversion of atoms of one element to atoms of another element)
Bombarded uranium-235 with high-energy neutrons (produce more massive elements)
Instead, produced isotopes of Barium
Lise Meitner and Otto Frisch (1939) explained the results of the experiments

23. Section 10.4 Fission and Fusion
Uranium-235 nuclei broken into smaller fragments (nuclear fission)
Def.-the splitting of an atomic nucleus into two smaller parts
Krypton-91, Barium-142, and Energy
Key Concept: In nuclear fission, tremendous amount of energy can be produced from very small amounts of mass.

24. Nuclear Fission of Uranium-235
Figure 18
Nuclear Fission of Uranium-235

25. Section 10.4 Fission and Fusion
Converting Mass Into Energy
When fission occurs, some of the mass of the reactants is lost.
Lost mass is converted into energy.
**Einstein (30 years before fission) introduced the mass energy equation: E=mc2
Equation described how mass and energy relate
E=energy; m=mass; c=speed of light (3.0 x 108 m/s)

26. Section 10.4 Fission and Fusion
Converting Mass Into Energy
Small amount of mass = release an enormous amount of energy
Large amount of energy = small amount of mass
Law of conservation of mass and energy-the total amount of mass and energy remains constant

27. Section 10.4 Fission and Fusion
Triggering a Chain Reaction
Nuclear fission can follow a pattern where one reaction leads to a series of others.
Def.-neutrons released during the splitting of an initial nucleus trigger a series of nuclear fissions.
Speed of chain reactions can vary.
Uncontrolled-all of the released neutrons are free to cause other fissions (fast and intense release of energy) Ex. Nuclear weapons

28. Section 10.4 Fission and Fusion
Triggering a Chain Reaction
Controlled-some neutrons absorbed by nonfissionable materials (1 new fission for each splitting of an atom)
Heat-used to generate electrical energy
Disadvantage-radioactive waste
Sustain a chain reaction: each nucleus that’s split must produce one neutron that causes the fission of another nucleus
Critical mass-smallest possible mass of a fissionable material that can sustain a chain reaction

29. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

30. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

31. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

32. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

33. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

34. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

35. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

36. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

37. Chain Reaction of Uranium-235
Figure 19
Chain Reaction of Uranium-235

38. Section 10.4 Fission and Fusion
Nuclear Energy from Fission
Nuclear power plants-20% of electricity in U.S.
Controlled fission of uranium-235; done in vessel (fission reactor)
Nuclear power plants: no air pollutants
Safety and environmental issues: employee protection, radioactive waste (isolated and stored), lose control of fission reactor (core melts b/c cooling system fails {meltdown}); radioactive material may be released, structure housing reactor is not secure=environment can be contaminated

39. Section 10.4 Fission and Fusion
Also releases huge amounts of energy
Def.-a process in which the nuclei of two atoms combine to form a larger nucleus
Same as fission: a small fraction of the reactant mass is converted into energy
Sun and stars powered by fusion of H and He
Sun : 600 million tons of H undergo fusion each second; 4 million tons of it is converted to energy

40. Section 10.4 Fission and Fusion
Require extremely high temperatures
Sun: temps. can reach 10,000,000 C (matter exists as plasma)
Plasma-a state of matter in which atoms have been stripped of their electrons
Gas (nuclei and electrons)
Future: may provide an efficient and clean source of electricity

41. Section 10.4 Fission and Fusion
Plan: fusion reactors fueled by 2 hydrogen isotopes: deuterium and tritium (produce helium, neutrons, and energy)
Problem: Achieving high temperatures required to start the reaction; containing the plasma