CP Text: Chapter 25
Notes: Nuclear Chemistry
● NUCLEAR REACTIONS:
● NUCLEAR FISSION:
● NUCLEAR FUSION:
● NUCLIDES:
-most nuclides have even # of protons and neutrons
● the neutron-to-proton ratio determines the stability of the nucleus:
-for low atomic #’s:
-above atomic #20:
● nuclei whose neutron-to-proton ratio is unstable undergo radioactive decay by emitting 1 or more particles and/or electromagnetic rays:
Type / Symbol /Identity
/ Mass (amu) / Charge / PenetrationAlpha
Beta
Gamma
Proton
Neutron
NUCLEAR EQUATIONS:
Example 1: Radium-226 transmutates by alpha decay. Write the nuclear equation that represents this process.
Example 2: Write the nuclear equation for the beta-decay of boron-12.
Example 3: Write the nuclear equation representing gamma radiation given off by the unstable radionuclide cobalt-60.
Nuclear Fission & Fusion
● FISSION:
*some elements fission spontaneously
* some elements can be induced to undergo fission when bombarded with other particles (e.g. neutrons)
● FUSION:
*the sun is a tremendous fusion reaction; the major fusion reaction in the sun is thought to be:
*both fission & fusion release large amounts of energy (fusion more than fission)
● The Atomic Bomb (FISSION)
-when the nucleus of U-235 splits, 2 isotopes are formed, plus neutrons are emitted
-these neutrons collide with other U-235 atoms, causing them to undergo fission; they release neutrons, and so on…
The Result…
CHAIN
REACTION!!
-there is a minimum mass of fissionable material that must be used to sustain a chain reaction: CRITICAL MASS!
-1 type of bomb:
● Nuclear Reactors (FISSION)
*use subcritical masses of fissionable material
● CORE:
*control rods: absorb neutrons
*pull rods out of core: fission increases
*push rods back into the core: fission decreases
**Safety feature: if power is lost, rods will automatically fall into the core and shut the reaction down.
TO GENERATE ELECTRICITY:
1)
2)
3)
4)
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CP Text: Chapter 25
PROS OF NUCLEAR ENERGY:
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CONS OF NUCLEAR ENERGY:
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CP Text: Chapter 25
Half-life and Radioactivity
Half-life (t1/2):
–The half-life of a sample of a radioactive isotope is the ______
required for ______of it to decay
–After each half-life, ______of the existing radioactive ______
have decayed into ______of a new ______.
Use half-lives of some radioisotopes found in nature to determine the ______of ancient artifacts
TEXTBOOK pg. 804
1. What percent of the atoms remains after 1 half-life?
2. What percent of the atoms remains after 2 half-lives?
3. Approximately how many half-lives does it take for 12.5% of the radioisotope to remain?
4. Compared to the energy liberated per gram during a typical chemical reaction, the amount of energy liberated per gram during the decay of a radioisotope is:
A. somewhat greater
B. less
C. much greater
D. about the same
Do #51 on pg. 822 of text (Decay curve for thorium-234)
A. What percent of the isotope remains after 60 days?
B. How many grams of a 250 g sample of thorium-234 would remain after 40 days had passed?
C. How many days would pass while 44 g of thorium-234 decayed to 4.4 g of thorium-234?
D. What is the half-life of thorium-234?
HALF – LIFE CALCULATIONS:
1. Carbon-14 emits beta radiation and decays with a half-life of 5730 years. Assume you start with a mass of 2.00 x 10-12 g of carbon-14.
a. How long is 3 half-lives?
b. How many grams of the isotope remain at the end of 3 half-lives?
2. Manganese-56 is a beta emitter with a half-life of 2.6 hours.
–What is the mass of manganese-56 in a 1.0 mg sample of the isotope at the end of 10.4 hours?
3. A sample of thorium-234 has a half-life of 24.1 days. Will all the thorium undergo radioactive decay in 48.2 days?
Explain
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