Chemistry

“Isotopes,

Decay &

Half Lives”

Name: ___________________________________________ Hour: ______________ Teacher: ROZEMA

Isotopia Stable and Radioactive Isotopes

Purpose To explore the naturally occurring isotopes of the elements.

Part 1: Elements 1 through 6

The chart shows the isotopes that exist for the first six elements. Use your periodic table to fill in the shaded boxes. Then answer the questions about the graph. 1. How many isotopes does hydrogen have? How do they differ? 2a) If you had a sample of beryllium, would all the atoms be identical? How do you know from the chart? 2b) What if you had a sample of lithium? Would they all be identical? Explain your answer using the chart..

3. Fill in the table regarding the protons and neutrons for the isotopes of carbon:

Carbon-12 Carbon-13 Carbon-14

Protons

Neutrons

Part 2: All the Naturally Occurring Isotopes Look at the Handout: Chart of Naturally Occurring Isotopes

4. Phosphorus (element #15) has one naturally occurring isotope. Write its name and symbol. Do the same for fluorine (#9) and scandium (#21). 5a) Potassium (#19) has three isotopes on the chart. Write their names and symbols. Which isotope is the RADIOACTIVE one? Circle it. 5b) Determine the number of protons and neutrons for all the isotopes in 5a. 6. Neodymium (#60) is used in very strong magnets. How many isotopes does it have? Write the names and symbols for the radioactive isotopes. 7. Where do most of the radioactive isotopes exist on the periodic table? Are these elements generally bigger or smaller than the non-radioactive isotopes? Explain. b) What do you think it means if something is “radioactive?”

Alpha Decay (Computer Lab Work)

Directions: Open Google Chrome, type in “Phet alpha decay”

1. Investigating “Alpha Decay”

a. At the top of the screen, click on the Single Atom tab

b. Observe the decay of Polonium-211. Try to pause the simulation when something gets “shot out” of

the nucleus. What particle is getting “shot out” of the nucleus? (Be sure to look at the legend in the upper right-hand corner of the screen to tell what this particle is.)

c. Using your periodic table, write the isotope symbol for Polonium-211. Determine the number of protons and neutrons for this isotope.

Symbol:

d. What is remaining AFTER the particle is shot out of the nucleus? Use your periodic table and write the name and symbol, and determine the protons and neutrons. Name and Symbol:

e. In your own words, describe what is happening to Polonium-211 when it undergoes “Alpha Decay.” Is the atom getting bigger, smaller, or staying the same size? Why do you think this?

Mass of isotope

Number of Protons

Number of neutrons

Mass of isotope

Number of Protons

Number of neutrons

2. When alpha decay happens, it is called a NUCLEAR process. Why do you think it is called this? (think about what the word “nuclear” and how it relates to the atom) 3. The nuclear reaction for the alpha decay of polonium-211 is shown below:

𝑃𝑜84211 → 𝐻𝑒2

4 + 𝑃𝑏82207

a) What do you notice about the mass number (numbers on top) of the reaction? b) What do you notice about the charge numbers/atomic numbers (numbers on the bottom) of the reaction? 4. Try to complete the nuclear reactions for the following alpha decay processes. Use your periodic tables!

𝑅𝑎88226 → 𝐻𝑒2

4 + _______

𝐺𝑑64148 → 𝐻𝑒2

4 + _______

𝑈92238 → 𝐻𝑒2

4 + _______

Beta Decay (Computer Lab Work)

Directions: Open Google Chrome, type in “Phet alpha decay”

2. Investigating “Beta Decay”: a. At the top of the screen, click on the Single Atom tab, click on Carbon-14 at the right-hand side.

b. Observe the decay of Carbon-14. Try to pause the simulation when something gets “shot out” of the

nucleus. What particles are getting “shot out” of the nucleus? (Be sure to look at the legend in the upper right-hand corner of the screen to tell what this particle is.)

c. Using your periodic table, write the isotope symbol for Carbon-14. Determine the number of protons and neutrons for this isotope.

Symbol:

d. What is remaining AFTER the particle is shot out of the nucleus? Use your periodic table and write the name and symbol, and determine the protons and neutrons.

Name and Symbol:

e. In your own words, describe what is happening to Carbon-14 when it undergoes “Beta Decay.” Is the atom getting bigger, smaller, or staying the same size? Why do you think this?

Mass of isotope

Number of Protons

Number of neutrons

Mass of isotope

Number of Protons

Number of neutrons

2. The nuclear reaction for the beta decay of Carbon-14 is shown below.

𝐶614 → 𝑒−−1

0 + 𝑁714

a) What do you think the second symbol (the e- symbol) is in this reaction? Why do you think this? What do you notice about the mass number (numbers on top) of the reaction? b) What do you notice about the charge numbers/atomic numbers (numbers on the bottom) of the reaction? 4. Try to complete the nuclear reactions for the following alpha decay processes. Use your periodic tables! The first one is also included in the simulation if you want to check your answer.

𝐻13 → 𝑒−−1

0 + _______

𝐶𝑎2047 → 𝑒−−1

0 + _______

𝑀𝑔1223 → 𝑒−−1

0 + _______

Collecting Beta Decay Data (Computer Lab Work)

Directions: Open Google Chrome, type in “Phet beta decay”

Your group will study an atom with a half-life of _______ years. To gather data, follow this procedure:

1. Click on “Custom” nucleus at the right of the screen.

2. For this experiment, you will need to collect data every 2.5 years on the chart. Confirm with your group where every 2.5 years will be on the graph.

To measure where 2.5 years is on the simulation, line up the arrow (on a blank piece of paper at

the back of this section) with the arrow on the simulation. Mark off where 10, 20, and 30 years is on your paper.

With your pencil, mark off the half-way points between the numbers are (5, 15, and 25 years) on your paper.

With your pencil, mark off half-way between these lines is on your paper (2.5, 7.5, 12.5, 17.5, 22.5, 27.5 years)

3. Adjust the Half-life arrow to your half life. KEEP THIS ARROW HERE THE ENTIRE SIMULATION!

4. Add 100 atoms to the screen. Hit “Pause” on the simulation.

5. Click on “Reset All Nuclei” and click on the button.

6. Person 1 should hold up your paper to the arrow on the screen.

7. Person 2 should click the button to start the simulation.

8. When the atom cloud hits each mark on your paper, Person 2 should pause the simulation.

9. Write down (IN THE DATA TABLE) the number of nuclei NOT DECAYED in the table.

10. Unpause the simulation until the atom clouds hits the next mark. Pause, take down data (IN THE DATA TABLE), and repeat until the atom cloud gets to 30 years.

Data Table: Time (years) Number of

nuclei remaining (not decayed)

Data from a second trial

Average data

0 99

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

Tim

e (y

rs)

0.0

AFTER YOU FINISHED EVERYTHING ELSE: (Take a ruler, make “tick marks” on the arrow at the following measurements: 1.4 cm, 2.9 cm, 4.4 cm, 5.9 cm, 7.4 cm, 8.9 cm, 10.3 cm, 11.7 cm, 13.2 cm, 14.7 cm, 16.1 cm, 17.6 cm) Then label your tick-marks with the times, in years, listed in the table. The zero mark has been labeled for you already.

Summary Notes: