Materials Included In Kit

Prelab Preparation

Photocopy a set of game directions for each group of students.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of 6 or for 5 groups of students. At least one game may reasonably be completed in a typical 45- to 50-minute class period. The Preactivity Questions on the worksheet may be completed before playing the games, and the Post-Activity Questions on the worksheet may be completed the day after the activity.
• The instructor should become familiar with the two games before students play them.

Teacher Tips

• This activity is appropriate for the study of atomic structure, elements and the periodic table. Playing the card games will help students remember the locations of the elements in the Periodic Table.
• Students should have a basic understanding of the atomic model and be somewhat familiar with the periodic table.
• The discovery of the neutron by James Chadwick (1891–1974) was one of the remaining puzzle pieces needed to explain isotopes. Visit the Nobel Prize website at http://nobelprize.org/ to learn more about Chadwick’s work as well as the work of the other scientists mentioned in the Background section.
• Most of the isotopes used in medicine are manufactured radioisotopes. These artificial isotopes are not naturally occurring. They are produced in nuclear reactors or cyclotrons by bombarding a non-radioactive target element with high energy particles— neutrons, protons, alpha particles, etc.
• The discovery of the uranium-235 isotope and its ability to cause a fission chain reaction led to the development of the first atomic bomb. U-235 was separated from the more abundant isotope, U-238, by electromagnets in a device known as a calutron. A vaporized sample of uranium ions was accelerated and deflected by a magnetic field. The less massive U-235 was deflected more than U-238 and was then able to be collected. This was a time consuming and costly method. Today U-235 is obtained by a gas diffusion method.
• All the isotopes depicted on the cards are naturally occurring. Visit the following website, http://www.webelements.com/webelements/elements/text/periodictable/isot.html (accessed June 2007) to find out more about the percentages of natural abundance and applications for each isotope.
• The following student laboratory kits can be used for more hands-on activities involving atomic structure and isotopes—“Bean Bag” Isotopes (Flinn Catalog No. AP6633) and Naming Atoms—Elements, Ions and Isotopes (Flinn Catalog No. AP6441).

Answers to Prelab Questions

1. Hydrogen has three naturally occurring isotopes—H-1, H-2 and H-3. Determine the number of protons and neutrons in each isotope of hydrogen.

   H-1 has 1 proton and no neutrons, H-2 has 1 proton and 1 neutron, and H-3 has 1 proton and 2 neutrons.

2. An isotope has a mass number of 235 with 143 neutrons. Use Equation 1 and the periodic table to determine the element.

   The isotope has an atomic number of 92 (235 – atomic number = 143). The element with an atomic number of 92 is uranium.

3. Consider the following two atoms—iron-56 and an atom with 27 protons and 29 neutrons. Are the atoms isotopes of the same element? Why or why not?

   These two atoms are not isotopes of the same element for two reasons—they have the same mass number (isotopes have different mass numbers), and the atomic number of iron is 26 (the other atom is cobalt, with 27 protons).

Answers to Questions

Use the periodic table to match the isotopes in the first column with their corresponding numbers of protons and neutrons in the second column.

7. The atomic mass of an element represents a weighted average of the mass of each isotope and its relative abundance. Neon has three naturally occuring isotopes—Ne-20, Ne-21 and Ne-22. The atomic mass of neon is 20.18. Which of the three isotopes is most abundant? Explain.

   Ne-20 is the most abundant isotope because the average mass is close to 20.

8. Explain why the mass number of an isotope is a whole number and the atomic mass of an element is usually a decimal number.

   The mass of an isotope is the number of protons and neutrons in the nucleus, thus it must be a whole number. The atomic mass is an average of the mass and relative abundance of all the isotopes of an element, therefore, it is usually a decimal number.

Teacher Handouts

12636_Teacher1.pdf

References

Lawrence and His Laboratory, Episode 2: The Calutron.

Introduction

In the early 1800s, John Dalton (1766–1844) proposed his new atomic theory—all atoms of the same element are identical and equal in mass. It was a simple yet revolutionary theory, yet not quite right. The discovery of radioactivity in the 20th century made it possible to study the structure and mass of atoms. Gradually, evidence was obtained that atoms of the same element could have different masses. These atoms were called isotopes. How are isotopes different from one another?

Concepts

• Atomic number
• Isotope
• Mass number

Background

An experiment by J. J. Thomson (1856–1940) led to the discovery of isotopes. Positively charged atoms in a gas discharge tube were bent by electric and magnetic fields and allowed to strike a photographic film, leaving “spots” on the film. The curve of each spot was dependent on the mass of the atoms. When using neon gas in 1912, Thomson obtained two curved spots. The major spot corresponded to neon atoms with a mass of about 20 atomic mass units (amu) and a much fainter spot, at a different angle, corresponded to neon atoms with a mass of about 22 amu.

In 1913, Frederick Soddy (1877–1956) used the term isotope to define atoms of the same element having the same properties but different atomic masses. Isotope was derived from Greek words meaning “same place”—isotopes occupy the same place in the periodic table since they are the same element. Since the identity of an element depends on the number of protons (the atomic number), isotopes have the same chemical properties—they undergo the same reactions, form the same compounds, etc. The only difference is that one isotope of an element has a different number of neutrons than another isotope of the same element.

The mass number of an isotope is the total number of protons and neutrons in the nucleus. The number of neutrons in the nucleus of an isotope is determined by subtracting the atomic number from the mass number (Equation 1). Chlorine, for example, occurs in the form of two isotopes, chlorine-35 and chlorine-37, where 35 and 37 are the mass numbers. Since the atomic number of chlorine is 17, chlorine-35 has 17 protons and 18 neutrons and chlorine-37 has 17 protons and 20 neutrons.

Experiment Overview

In this activity, identify isotopes by playing two different card games—It’s a Match! and Got Isotopes?

Materials

Procedure

Before playing the games, answer the Preactivity Questions on the Isotope Identity Worksheet. Refer to the directions for specific instructions for each game. Be sure to return all cards to the original container when finished with the game.

Student Worksheet PDF

12636_Student1.pdf