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

• http://www.youtube.com/watch?v=KWAsz59F8gA

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

Nuclear Chemistry • Atomic nucleus: compared to the whole atom

• (also called the nuclide) • Mass:

• Energy

• Volume

Student notes

Strong Nuclear Force:Holds the nucleus together

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

Nuclear Chemistry • Most atoms have tremendously stable nucleus

• Exist for billions of years

• A radioactive isotope has an unstable nucleus which undergoes spontaneous changes. • Note: spontaneous change ⇏ fast change

• Transmutates into another element • The nucleus changes (different number of protons):

• Emits particles and energy:

Unstable isotopes are changing to become stable

Student notes

Types of Radiation Understand the following slides on radiation emissions to complete the table in your notes.

Alpha Decay

Beta decay

Gamma Decay

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

Next slide

Penetrating ability of different particles:Radition strength: how each of the radioactive emissions are blocked.Which is the most damaging (strongest)?

Nuclear reactions • Represents the nuclear changes

• Use symbols to represent

• The isotope before and after the change • The particles which are emitted• Before and after must balance

Balancing Nuclear Reactions

• Student notes: • Totals number of atomic numbers (A ) and total mass

numbers (Z) must be the same before and after the reaction.

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

• Shown by “Before” “ After”

Nuclear reactionsStudent notesTotal 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

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 decayStudent notes: 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

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isot

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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)?