Chemical Element Set

Background

Element sets provide the opportunity for chemistry teachers to teach in a more hands-on, descriptive manner. All too often students are expected to learn names and symbols for elements that they have never seen. It is not surprising that students sometimes find this a frustrating and difficult task. The teaching of chemistry will appeal to more students if they are able to connect names and symbols with real elements having real properties.

The element set contains 24 element samples, which are listed below according to their position in the periodic table. Notice that the set contains all of the members of one family of elements—Group 14 (C, Si, Ge, Sn, Pb)—and many members of one series of elements—Period 4 (Ca, Cr, Mn, Fe, Ni, Cu, Zn, Ge, As, Se, Br). The inclusion of elements within a group and across a period makes it possible to explore periodic trends in the properties of the elements.

The following are some suggested activities for the element set.

1. Element of the Week: Place a new element on your desk each week. Assign the students the task of researching the element and preparing a written report. Written reports should include the element’s symbol, atomic number, atomic weight, density, appearance (luster), discovery, sources, as well as interesting facts about the element and its uses. The CRC Handbook of Chemistry and Physics, the Merck Index and the Web Elements website (www.webelements.com/webelements/index.html) are useful references for this assignment.
2. Period/Group Relationships: When discussing a period or group of elements, show students the member elements. Discuss periodic trends in their properties (e.g., density, reactivity).
3. Metals versus Nonmetals: Place a small piece of as many elements as possible on a copy of the periodic table. Use only the elements that come in pieces, and glue or tape the elements in place. Have students test the conductivity of the elements and record the results on the periodic table. A description of an inexpensive, semiquantitative conductivity probe is included. [Note: Silicon will conduct slightly due to minor impurities (essentially the same principle as semiconductor doping). An ultra pure sample of silicon prepared for manufacturing computer chips will not conduct.]
4. Making Compounds: Students often have difficulty understanding how the properties of compounds can be so different than the elements from which they are made. A useful project for students is to choose a compound and place a small sample in a vial or a test tube. Samples of the elements that make up the compound should be placed in separate vials. For example, copper sulfate would be exhibited next to samples of copper, sulfur and oxygen. To make this activity economical, segregate the elements and compounds that are available. The vials can be emptied back into these bottles at a later time and the chemicals can be reused for this project each year. Be careful to prevent accidental mixing of chemicals.
5. Reactivity Trend of Magnesium and Calcium: For this activity, the students will need matches, litmus paper, two test tubes, two small funnels and two beakers, each large enough to hold the funnel in an inverted position. Place water in the beaker. Drop a sample of calcium or magnesium into the water. Place the inverted funnel over the sample (see Figure 2). Invert the test tube over the funnel stem so that any gas generated by the reaction can be collected. Test for the presence of hydrogen by removing the test tube from the funnel stem and placing a lighted match in the mouth of the test tube. The hydrogen gas will pop loudly! Test the water in the beaker with litmus paper to confirm the presence of hydroxide ion. Students should compare the reactivity of the two metals, describe the periodic trend, and write equations for the observed reactions. Calcium is much more reactive than magnesium, which does not react with cold water. By warming the water containing the magnesium, students can also observe the effect of heat on a reaction rate.
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6. Allotropic Forms of Carbon: Have students compare the “feel” of graphite powder and charcoal powder. The graphite supply can be replenished at the hardware store. With the conductivity probe, have students compare the conductivity of charcoal versus pencil lead (which consists of graphite and binder).
7. Creative Additions: Add to your element set in a creative way. For example, an “empty” beaker demonstrates the presence of nitrogen or oxygen. Fill a balloon with helium. Silver and gold are found in jewelry and (some) coins. Discarded neon advertising signs contain the inert gas. Encourage students to read labels and locate samples of elements.

If you are rigorous about showing the elements as you talk about them, your students’ expectation levels will change. They will expect to see chemicals, especially the exotic-sounding ones, such as iron(III) nitrate nonahydrate. They will start asking questions: “Will gallium really melt in your hand?” “Can you see a difference between ferric chloride and ferrous chloride?” Be prepared! Start building your collection of elements and compounds now.

Student Worksheet PDF

13347_Student1.pdf

Answers to Questions

1. Name at least three physical properties of metals.

   Possible answers may include—Luster (shininess), conductors of electricity and heat, high density, high melting point, ductile, malleable

2. What are two chemical properties of metals?

   Metals easily lose electrons to form cations and they are susceptible to corrosion (i.e., rusting of iron).

3. Name at least three physical properties of nonmetals.

   Possible answers may include—dull appearance (not lustrous), poor conductor of heat and electricity, brittle (breaks easily), low density, low melting point

4. What would be a general chemical property of nonmetals?

   Nonmetals tend to gain electrons to form anions.

5. What does the stair-step line on the periodic table separate? What is located on each side?

   The stair-step line allows identification of metals, nonmetals and metalloids. The elements to the left of the stair-step line are metals or metal-like elements. The elements to the right of the stair-step line are nonmetals.

Discussion

Supplementary Information

An Inexpensive, Semiquantitative Conductivity Probe
The Flinn Conductivity Meter (Catalog No. AP1493) is a semiquantitative device. It may be used to test the conductivity of metals, metalloids and nonmetals and to distinguish between strong and weak electrolytes or nonelectrolytes in solution. The Flinn Conductivity Meter uses green and red light emitting diodes (LEDs) to quantitatively measure the conductivity of a solid or solution. The green LED requires more voltage than the red LED. Immersing the electrodes into a solution of a weak electrolyte results in a dim glowing of the red LED while the green LED remains off. A strong electrolyte will cause both the red and green LEDs to glow. The meters contain an attached scale that can be used to measure and compare the conductivity of various samples. The meter is sufficiently sensitive that it will display low conductivity for 70% alcohol solutions and medium conductivity for tap water.

This conductivity meter is safe—no electric shock is possible because only a 9-volt battery is used. And, because it is battery operated, the device is entirely portable. The meter cannot easily be shorted out, particularly since an ON/OFF switch is provided to disconnect the circuit even during storage. The electrodes are easily interchanged or replaced.

References

Canzano, Carolyn, A Camille and Henry Dreyfus Institute Curriculum Module. Volume I, 1984, pp. 84–88. (This reference includes a laboratory designed for high school students.)

Feinstein, H. I., Journal of Chemical Education, Volume 49, April 1972, p. 268.