Transcript II. Kinds of Chemical Bonds

Chapter 11
Nuclear Chemistry
I.
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 number
Atomic Symbol
12C
6
Try Sodium on your own….
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…
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
III.
Transmutation of Elements (Cont’d)
 To sum up, the “rules” of radioactive
decay are:
1. Alpha Decay – nucleus loses 2 P’s and
2 N’s
2. Beta Decay – nucleus loses an electron
(the electron was produced by the
breakdown of a neutron)
3. Gamma Decay – accompanies Alpha
and Beta Decays – nucleus releases a
HIGH energy wave called a Gamma ray
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 U238 left in my sample?
• How much, and what decay material, would I have along with
my 300 g of U-238 (see your textbook) ?
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
92 Kr + 141 Ba + 3 1 n
• 235 U + 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 don’t use it as an energy source
This is how the SUN produces so much heat and radiation
energy
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
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
Practice of Half-Life Calculations
 Fill in this chart of the half-life decay of Carbon-14
Half Life #
0
1
2
3
4
Time Elapsed
0
5730
11460
17190
22920
Am’t of C14 Remaining
1600g
800g
400g
200g
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