Chemistry: Matter and Change

1
(No Transcript)
2
Section 24-1
Types of Radiation

• Isotopes of atoms with unstable nuclei are called
  radioisotopes.

3
Section 24-1
Types of Radiation (cont.)

• Alpha particles have the same composition as a
  helium nucleustwo protons and two neutrons.

• Because of the protons, alpha particles have a 2
  charge.
• Alpha radiation consists of a stream of particles.

4
Section 24-1
Types of Radiation (cont.)

• Gamma rays are high-energy electromagnetic
  radiation.

• Gamma rays have no mass or charge.
• X rays are a form of high-energy electromagnetic
  radiation emitted from certain materials in an
  excited state.

5
Section 24-1
Types of Radiation (cont.)

• The ability of radiation to pass through matter
  is called its penetrating power.

6
End of Section 24-1
7
Section 24-2
Nuclear Stability

• Except for gamma radiation, radioactive decay
  involves transmutation, or the conversion of an
  element into another element.

• Protons and neutrons are referred to as nucleons.

8
Section 24-2
Nuclear Stability (cont.)

• The strong nuclear force acts on subatomic
  particles that are extremely close together and
  overcomes the electrostatic repulsion among
  protons.

9
Section 24-2
Nuclear Stability (cont.)

• The area on the graph within which all stable
  nuclei are found is known as the band of
  stability.

10
Section 24-2
Types of Radioactive Decay

• Atoms can undergo different types of decaybeta
  decay, alpha decay, positron emission, or
  electron capturesto gain stability.

11
Section 24-2
Types of Radioactive Decay (cont.)

• Positron emission is a radioactive decay process
  that involves the emission of a positron from the
  nucleus.
• A positron is a particle with the same mass as an
  electron but opposite charge.

12
Section 24-2
Types of Radioactive Decay (cont.)

• Electron capture occurs when the nucleus of an
  atom draws in a surrounding electron and combines
  with a proton to form a neutron.

13
Section 24-2
Radioactive Series

• A series of nuclear reactions that begins with an
  unstable nucleus and results in the formation of
  a stable nucleus is called a radioactive decay
  series.

14
Section 24-2
Radioactive Decay Rates

• Radioactive decay rates are measured in
  half-lives.

• A half-life is the time required for one-half of
  a radioisotope to decay into its products.

15
Section 24-2
Radioactive Decay Rates (cont.)

• The process of determining the age of an object
  by measuring the amount of certain isotopes is
  called radiochemical dating.

16
End of Section 24-2
17
Section 24-3
Induced Transmutation (cont.)

• The process of striking nuclei with high-velocity
  charged particles is called induced transmutation.

18
Section 24-3
Induced Transmutation (cont.)

• Transuranium elements are the elements with
  atomic numbers 93 and higher, immediately
  following uranium.

19
Section 24-3
Nuclear Reactions and Energy

• Mass and energy are related.

• Loss or gain in mass accompanies any reaction
  that produces or consumes energy.
• ?E ?mc2 where E represents energy in Joules, m
  mass in kg, and c the speed of light.

20
Section 24-3
Nuclear Reactions and Energy (cont.)

• The mass of a nucleus is always less than the sum
  of the masses of the individual protons and
  neutrons that comprise it.

• The difference between a nucleus and its
  component nucleons is called the mass defect.

21
Section 24-3
Nuclear Fission

• The splitting of nuclei into fragments is known
  as nuclear fission.

• Fission is accompanied with a very large release
  of energy.

22
Section 24-3
Nuclear Fission (cont.)

• Samples with enough mass to sustain a chain
  reaction are said to have critical mass.

23
Section 24-3
Nuclear Reactors (cont.)

• The reactor core contains a reflector that
  reflects neutrons back into the core, where they
  react with fuel rods.

• Breeder reactors produce more fuel than they
  consume.

24
Section 24-3
Nuclear Fusion

• The combining of atomic nuclei is called nuclear
  fusion.
• Nuclear fusion is capable of releasing very large
  amounts of energy.

25
Section 24-3
Nuclear Fusion (cont.)

• Fusion has several advantages over fission.

• Lightweight isotopes are abundant.
• Fusion products are not radioactive.
• However, fusion requires extremely high energies
  to initiate and sustain a reaction.

26
Section 24-3
Nuclear Fusion (cont.)

• Fusion reactions are also known as thermonuclear
  reactions.

27
End of Section 24-3
28
Section 24-4
Detecting Radioactivity

• Radiation with enough energy to ionize matter it
  collides with is called ionizing radiation.

• The Geiger counter uses ionizing radiation to
  detect radiation.

29
Section 24-4
Detecting Radioactivity (cont.)

• A scintillation counter detects bright flashes
  when ionizing radiation excites electrons of
  certain types of atoms.

30
Section 24-4
Uses of Radiation

• A radiotracer is a radioactive isotope that emits
  non-ionizing radiation and is used to signal the
  presence of an element or specific substrate.

31
Section 24-4
Uses of Radiation (cont.)

• Radiation can damage or destroy healthy cells.

• Radiation can also destroy unhealthy cells, such
  as cancer cells.
• Unfortunately, radiation therapy also destroys
  healthy cells in the process of destroying
  cancerous cells.

32
Section 24-4
Biological Effects of Radiation

• Radiation can be very harmful.

• The damage depends on type of radiation, type of
  tissue, penetrating power, and distance from the
  source.

33
Section 24-4
Biological Effects of Radiation (cont.)

• High energy radiation is dangerous because it
  produces free radicals.

• Free radicals are atoms or molecules that contain
  one or more unpaired electrons.
• Free radicals are highly reactive.

34
Section 24-4
Biological Effects of Radiation (cont.)

• Two units measure doses of radiation.

• The rad stands for Radiation-Absorbed Dose, which
  is the amount of radiation that results in 0.01 J
  of energy per kilogram of tissue.
• The rad does not account for the type of tissue
  that is absorbing the radiation.
• The rad is multiplied by a factor related to its
  effect on the tissue involved and is called the
  rem, Roentgen Equivalent for Man.