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 / Penetration
Alpha
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:

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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