Chapter 11 Nuclear Chemistry

1
Chapter 11 Nuclear Chemistry
2
Radioactive Elements

• Radioactivity release of energy and matter from
  changes in an atoms nucleus
• Some elements or some of their isotopes (atoms w/
  different mass s) are radioactive
• A new way to write an atomic symbol
• mass number Atomic Symbol
• atomic number
• 12C
• 6
• Try Sodium on your own.

3
II. Transmutation of Elements

• Transmutation or Radioactive Decay change of
  one element to another (e.g., U changing to Pb)
• Decay Series series of steps by which a
  radioactive nucleus changes to a nonradioactive
  one (Fig 11-6)
• Alpha Decay when a nucleus releases 2 protons
  and 2 neutrons together ( a He nucleus)
• Beta Decay when a nucleus releases an electron
• But wait Mrs. OGorman, you told us that
  electrons are not in the nucleus
• Well, scientists believe that a neutron is
  nothing but a proton and an electron that are
  hooked up and disguised as a neutral charge

4
III. Transmutation of Elements (Contd)

• Gamma Decay release of energy in the form of
  gamma rays that accompanies a (alpha) and ß
  (beta) decay
• Decay or die! (try these)
• Illustrate the alpha decay of Polonium 216
• Illustrate the beta decay of Bismuth 210

5
III. Transmutation of Elements (Contd)

• To sum up, the rules of radioactive decay are
• Alpha Decay nucleus loses 2 Ps and 2 Ns
• Beta Decay nucleus loses an electron (the
  electron was produced by the breakdown of a
  neutron)
• Gamma Decay accompanies Alpha and Beta Decays
  nucleus releases a HIGH energy wave called a
  Gamma ray

6
II. Transmutation of Elements

• Half-life amount of time it takes half the
  atoms in a sampleof radioactive material to decay
  into a stable, non-radioactive element (Fig.
  11-12)
• Half-life of Polonium-215 is 0.0018 second
• Half-life of Uranium-218 is 4.5 billion years!!
• Suppose you have 100 grams of Po-215
• How much Po is left after 0.0018 seconds?
• After 0.0036 sec?
• After 0.0072 sec?
• Suppose you are given 600 g of U-238
• How large was the sample 2.25 billion years ago?
• In how many years would I expect to see ONLY 300
  g of U-238 left in my sample?
• How much, and what decay material, would I have
  along with my 300 g of U-238 (see your textbook)
  ?

7
III. Transmutation of Elements

• Nuclear Fission
• Splitting of a large atom into two smaller ones
  by a neutron bullet
• Releases energy
• Can be controlled so its used for nuclear power
• INDIAN POINT FISSION
• 235 U 1 n 92 Kr 141 Ba 3 1 n
• 92 0 36 56 0
• Nuclear Fusion
• fusing of two smaller atoms to form a larger one
• TREMENDOUS Release of energy
• Difficult to control so we dont use it as an
  energy source
• This is how the SUN produces so much heat and
  radiation energy
• FUSION SUN

8
IV. Detecting Measure Radioactivity

• Electroscope (Fig. 11-17)
• Separated foil leaves collapse if a radiation
  source is near
• Geiger Counter (Fig. 11-18)
• Makes a click every time a radiation particle
  hits it
• of clicks per unit time indicates the radiation
  strength
• Cloud chamber (Fig. 11-19)
• Radiation particles leave visible trails through
  alcohol vapor
• Bubble chamber (Fig. 11-20)
• Similar to a cloud chamber

9
V. Uses of Radioactivity

• Radioisotopes artificially produced radioactive
  isotopes of common elements
• Used as tracers whose paths can be followed with
  instruments
• Iodine-131 collects in the thyroid gland so
  doctors can observe any problems that a person my
  be having with their thyroid.
• Iron-59 collects in blood
• Some food is irradiated to kill bacteria so it
  will stay safe to eat for long periods of

10
Practice of Half-Life Calculations

• Fill in this chart of the half-life decay of
  Carbon-14
• Half Life Time Elapsed Amt of C14 Remaining
• 0 0 1600g
• 1 5730 800g
• 2 11460 400g
• 3 17190 200g
• 4 22920 100g
• - In what year will you have half of the amount
  of radioactive material than what you started
  with (assuming that the decay process starts
  today)?
• - 7737
• How many years will it take to have 25 of what
  you started with?
• 11,460 years