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Chapter 11 Nuclear Chemistry

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1 Chapter 11 Nuclear Chemistry

2 Radioactive Elements Radioactivity – release of energy and matter from changes in an atom’s 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. O’Gorman, 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 (Cont’d)
Gamma Decay – release of energy in the form of gamma rays that accompanies α (alpha) and β (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 (Cont’d)
To sum up, the “rules” of radioactive decay are: Alpha Decay – nucleus loses 2 P’s and 2 N’s 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 ) Half-life of Polonium-215 is 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 seconds? After sec? After 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 it’s used for nuclear power INDIAN POINT = FISSION 235 U + 1 n Kr Ba n Nuclear Fusion fusing of two smaller atoms to form a larger one TREMENDOUS Release of energy Difficult to control so we don’t 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 ) Separated foil leaves collapse if a radiation source is near Geiger Counter (Fig ) Makes a click every time a radiation particle hits it # of clicks per unit time indicates the radiation strength Cloud chamber (Fig ) Radiation particles leave visible trails through alcohol vapor Bubble chamber (Fig ) 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 Am’t of C14 Remaining g g g g g - 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

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