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Nuclear Chemistry

Bravo – 15,000 kilotons

Types of Radioactive Decay

2+

- alpha production (a): helium nucleus
- beta production (b): neutron splits into an electron and a proton

CREATING A REACTION (α-particle)

- On either side of the arrow, the mass number and atomic number MUST be the same (alpha-particle is always a helium nucleus)

238U 4He + 234Th

92 2 90

- On the left side, mass number is 238
- On the right side, 234 + 4 = 238
- On the left side, the atomic number is 92
- On the right side, 90 +2 = 92

CREATING A REACTION (β-particle)

- Both sides of the reaction still need to balance.
- In beta-radiation, a neutron splits apart to form an electron and a proton

234Th + 234Pa 0e

90 91 -1

- On the left side, mass number is 234
- On the right side, 234 + 0 = 234
- On the left side, the atomic number is 90
- On the right side, 91 - 1 = 90

Alpha Radiation

Limited to VERY large nucleii.

Beta Radiation

Converts a neutron into a proton.

PRACTICE

- Each of the following compounds emits an alpha particle, write the balanced nuclear reaction
- 222Ra

88

- 208Po

84

PRACTICE

- Each of the following compounds emits a beta particle, write the balanced nuclear reaction
- 14C

6

- 131I

53

Types of Radioactive Decay

- gamma ray production (g):
- positron production:
- electron capture: (inner-orbital electron is captured by the nucleus)

GAMMA RADIATION

- Gamma radiation does not produce any particles by itself
- It is tied to another radioactive decay
- Because the release of radioactive particles “frees” some energy in the nucleus, this energy takes the form of gamma radiation
- There is a lot of energy holding the nucleus together so gamma radiation has a LOT of energy

Positron and Electron capture

- Positron emissions occur when a proton splits apart into a neutron and an electron
- Therefore the mass number does not change, but the atomic number changes the element into something new
- Electron capture occurs when a proton “captures” one of the inner valence electrons and converts it into a neutron
- This causes the release of a powerful neutrino (as powerful as gamma radiation)

ANOTHER WAY TO SYMBOLIZE ISOTOPES

- So far we have seen one way to symbolize isotopes:
- 17F

9

- 31S

16

- Since we know the number of protons, we can symbolize the isotope with just the mass number:
- Fluorine-17
- Sulphur-31

Deflection of Decay Particles

attract

Opposite charges_________ each other.

repel

Like charges_________ each other.

NuclearStability

Decay will occur in such a way as to return a nucleus to the band (line) of stability.

HALF LIFE

- When an isotope goes through a radioactive emission, it does so at a fairly constant rate
- Scientists use this property to date items
- Half-life: The time it takes for ½ of a radioactive isotope to decay to a stable form
- Example: Carbon-14 has a half life of 5730 years
- It takes 5730 years for ½ of radioactive Carbon-14 to decay to the stable form or Nitrogen-14
- 14C 0e + 14N

6 -1 7

HOW TO SOLVE HALF-LIFE

- Iodine-131 is used to destroy thyroid tissue in an over-productive thyroid gland. The half-life of iodine-131 is 8 days. If a hospital received a shipment of 200g of iodine-131, how much iodine-131 would remain after 32 days?

SOLUTION

- Step 1: Find out how many ½-lives have occurred
- (32 days/8 days for half-lives)
- 4 half-lives
- Step 2: Four each half-life, divide the sample by 2
- 4 half lives = ½ x ½ x ½ x ½ = 1/16
- Step 3: Divide the initial sample size
- 200g/16 = 12.5g will remain

TRY THIS

- Mercury-197 is used for kidney scans and has a half-life of 3 days. If the 32g of mercury-197 is ordered, but takes 15 days to arrive, how much would arrive with the shipment?

Nuclear Fission and Fusion

- Fusion:Combining two light nuclei to form a heavier, more stable nucleus.
- Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers.

Energy and Mass

Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein’s equation:

DE = Dmc2

Dm = mass defect

DE = change in energy

c = speed of light

Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.

Fission Processes

A self-sustaining fission process is called a chain reaction.

MORE PRACTICE PROBLEMS

- Nitrogen-13 emits beta radiation and decays to Carbon-13. This has a half-life of 10 minutes. You start with 2.0g of Nitrogen-13:
- Write out the balanced nuclear reaction.
- Calculate how much nitrogen-13 is remaining after 40 minutes.

MORE PRACTICE PROBLEMS

- Manganese-56 decays with beta radiation and has a half-life of 2.6 hours. You begin with 1mg of Manganese-56:
- Write the balanced nuclear reaction.
- How much manganese-56 is left after 10.4 hours?

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