NUCLEAR CHEMISTRYOBJECTIVE: TO EXPLAIN THE PROCESS OF RADIOACTIVE DECAY USING NUCLEAR EQUATIONS AND HALF LIFE

Essential Question: How do unstable (radioactive) isotopes become stable?

Radioactivity introduction -• Radioactivity video – 4 minutes• http://ed.ted.com/lessons/radioactivity-expect-the-unexpec

ted-steve-weatherall• Review questions:• http://ed.ted.com/lessons/radioactivity-expect-the-unexpec

ted-steve-weatherall#review• Dig deeper: • http://ed.ted.com/lessons/radioactivity-expect-the-unexpec

ted-steve-weatherall#digdeeper

Review: Radioactive IsotopesA radioactive isotope has an unstable nucleus that

undergoes spontaneous changes. - Emits particles

- 1.- 2.

- Emits energy in the form of __________ waves. - Transmutates into another element

Types of Radiation

Alpha Decay

Beta decay

Gamma Decay

Particles emitted from a radioactive isotopeType Symbol Charge Mass Rad.Strength

Next slide

Radiation Strength: Explain in your notes how each of the radioactive emissions are blocked.Which is the most damaging (strongest)?

Strong Nuclear Force:Holds the nucleus together

Limit to the # neutrons: A nucleus with too many neutrons will be unstable and change

Balancing Nuclear Reactions

• Keep track of atomic number (Z) and mass number (A): protons & neutrons

• Totals of A & Z must be the same before and after the reaction.

• Shown by “Before” “ After”

Nuclear reactionsTotal number of atomic numbers and the total mass

numbers must be equal on both sides of the equation. Examples:

Nuclear Equations

1. 23892U 234

90Th + ?

2. 146C 0

-1e + ?3. 239

94Pu + 42He 242

96Cm + ?

Nuclear Equations Practice Website

Nuclear Reactions Emission of Alpha or Beta particles

• http://phet.colorado.edu/en/simulation/beta-decay• http://phet.colorado.edu/en/simulation/alpha-decay

Radioactive decay

No two radioactive isotopes decay at the same rate. Therefore, decay rate can be used to identify the isotope. Decay is measured by half life.

Half-life• Measure of Radioactive decay rate.• Measured as the time it takes for ½ of a sample of

radioisotope’s nuclei to decay into its products.

Half Life

Decay of a radioisotopeNumber of Half-Lives

Elapsed time Amount remaining

0 0 100 g

1 1.5 year 50 g

2 3 years 25 g

3 4.5 years 12.5 g

• Examples of the Half Life of Radioactive Elements

Tearing Through a Half Life800 Billion Bismuth-210 Atoms

Time (years)

Half Life: • http://phet.colorado.edu/en/simulation/radioactive-dating-g

ame

Number of years

Num

ber o

f rad

ioac

tive

isot

opes

Fission and Fusion

• http://phet.colorado.edu/en/simulation/nuclear-fission

Half life Calculations• How much of a 100g sample of an unstable isotope

remains after 25 years if the half life is 5 years?• Determine how many “half life intervals”. • Calculate the amount of original sample remaining after

each ½ life100g

• Simplify the calculations

Half Life Problems• How much of a 100g sample of an unstable isotope

remains after 25 years if the half life is 5 years?

3.1 g

Half Life Problems• How much of a 60g sample of an unstable isotope

remains after 2 days if the half life is 12 hours?

7.5 g

Half Life Problems• How much of a 20 g sample of an unstable isotope

remains after 3 sec if the half life is 0.5 seconds?

Fission and Fusion

• http://phet.colorado.edu/en/simulation/nuclear-fission

ORIGINS OF ELEMENTReading Analysis:

Teachers' Domain: The Origin of the Elements

Teachers' Domain: The Elements: Forged in Stars

Got Calcium• Where are most elements created? • When was H and He created? • What elements are made by small stars?• What additional elements are made by large stars?• What elements are made by supernovae (large exploding

stars)?