Materials Included In Kit

Additional Materials Required

Safety Precautions

All materials used in this lab are nonhazardous and may be save for future labs. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information. 

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. 

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period. The Prelaboratory Questions may be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• Students can test the resistance of the graphite circuit with a multimeter. The procedure for this activity is in Flinn publication 10742, An Activity You Can’t Resist. Multimeters are available from Flinn Scientific (Catalog No. AP4639).

Answers to Prelab Questions

1. Which of the following exhibits ionic bonding?

1. NaCl
2. CH₄
3. I₂
4. Br₂

2. Which of the following exhibits covalent bonding?

1. NaCl
2. CuCl₂•2H₂O
3. CH₄
4. CuCl

3. Which of the following exhibits metallic bonding?

1. NaCl
2. CH₄
3. Al(s)
4. Cl₂

4. Select the polar molecule.

1. CH₄
2. I₂
3. F₂
4. H₂O

5. Select the nonpolar molecule.

1. H₂O
2. CH₃CH₂OH
3. HF
4. I₂

6. In this type of bonding, oppositely charged ions arrange themselves in an extended, tightly packed three-dimensional structure called a crystal lattice.

1. Polar covalent bonding
2. Nonpolar covalent bonding
3. Ionic bonding
4. Metallic bonding

7. In this type of bonding there are resulting net attrac¬tive forces from pairs of electrons that are shared between atoms.

1. Metallic bonding
2. Ionic bonding
3. Hydrogen bonding
4. Covalent bonding

8. In your own words, describe network covalent bonding.

In graphite, the carbon atoms are covalently bonded to three other carbon atoms in a 3-D array. Covalent bonding to three other carbon atoms leaves an unshared electron that can flow through the molecular structure. These electrons give graphite the ability to conduct electricity.

Answers to Questions

1. In the following space, draw a diagram of your modified graphite circuit from step 7 in the Procedure section. Include observations in complete sentences.

Introduction

Learn about different types of bonding with this hands on activity! The Background section covers the different types of bonding, and the Prelab Questions solidify these concepts. The lab portion involves a challenge with a specific type of bonding—network covalent. Follow the procedure to make a graphite circuit with a few simple materials—pencil lead, a 9–V battery and an LED. Then optimize the experiment to vary the brightness of the LED. Get prepared to be amazed and have some fun!

Concepts

• Chemical bonding
• Network covalent solids
• Ohm’s law
• Properties of solids

Background

Simply put, a chemical bond holds two or more atoms together. There are different types of chemical bonding: ionic, covalent and metallic. In ionic bonding there are attractive forces between oppositely charged ions in an ionic compound. An ionic compound is formed when a metal reacts with a nonmetal to form positively charged cations and negatively charged anions, respectively. The oppositely charged ions arrange themselves in an extended, tightly packed three-dimensional structure called a crystal lattice. The net attractive forces between oppositely charged ions in the crystal structure are called ionic bonds.

Covalent bonding represents another type of attractive force between atoms. Covalent bonds are defined as the net attractive forces resulting from pairs of electrons that are shared between atoms (the shared electrons are attracted to the nuclei of both atoms in the bond). A group of atoms held together by covalent bonds is called a molecule. Atoms may share one, two or three pairs of electrons between them to form single, double and triple bonds, respectively. Substances held together by covalent bonds are usually divided into two groups based on whether individual (distinct) molecules exist or not. In a molecular solid, individual molecules in the solid state are attracted to each other by relatively weak intermolecular forces between the molecules. Covalent-network solids, on the other hand, consist of atoms forming covalent bonds with each other in all directions. The result is an almost infinite network of strong covalent bonds—there are no individual molecules. Graphite, the solid to be tested in this lab experiment, is an example of a network covalent solid.

Experience the 360° activity to learn more about its unique properties and its importance in the successful completion of this lab activity.

Covalent bonds may be classified as polar or nonpolar. The element chlorine, for example, exists as a diatomic molecule, Cl₂. The two chlorine atoms are held together by a single covalent bond, with the two electrons in the bond equally shared between the two identical chlorine atoms. This type of bond is called a nonpolar covalent bond. The compound hydrogen chloride (HCl) consists of a hydrogen atom and a chlorine atom that also share a pair of electrons between them. Because the two atoms are different, however, the electrons in the bond are not equally shared between the atoms. Chlorine has a greater electronegativity than hydrogen—it attracts the bonding electrons more strongly than hydrogen. The covalent bond between hydrogen and chlorine is an example of a polar bond. Notice that the chlorine atom in HCl has a partial negative charge (δ–) while the hydrogen atom has a partial positive charge (δ+).

The special properties of metals compared to nonmetals reflect their unique structure and bonding. Metallic bonding describes the attractive forces that exist between closely packed metal cations and free-floating valence electrons in an extended three-dimensional structure. Metals typically have a small number of valence electrons available for bonding. The valence electrons appear to be free to move among all of the metal atoms, which must exist as positively charged cations.

Work through this set of six videos from Khan Academy to reinforce concepts of types of chemical bonding. https://www.khanacademy.org/science/chemistry/chemical-bonds

This lab involves building a graphite circuit. Think of the graphite circuit as a wired electrical system. Work in an electrical system is done by moving negatively charged particles called electrons. The movement of electrons in an electrical system is called electric current. Electric current cannot be seen because electrons are too small to be viewed, but its effect can be observed and measured. The motion of electrons traveling down a wire can be compared to the movement of water in a hose. Just like with water flowing through a hose, energy must be supplied to the electrons before they will move in a wire and provide energy to do work. The energy can be supplied by chemical means, like a battery, or by mechanical means, such as with a waterwheel in a river turning a generator.

You will be entertained when chemistry crosses physical science in this cool lab!

Experiment Overview

Answer the Prelaboratory Questions to reinforce the difference between the types of chemical bonding. With the listed materials and procedure, build your very own graphite circuit. Successful completion of the circuit will result in a lit red LED. Each student will have the opportunity to make their own circuit, partner up for collaboration and share materials. 

Materials

Prelab Questions

1. Which of the following exhibits ionic bonding?

1. NaCl
2. CH₄
3. I₂
4. Br₂

2. Which of the following exhibits covalent bonding?

1. NaCl
2. CuCl₂•2H₂O
3. CH₄
4. CuCl

3. Which of the following exhibits metallic bonding?

1. NaCl
2. CH₄
3. Al(s)
4. Cl₂

4. Select the polar molecule.

1. CH₄
2. I₂
3. F₂
4. H₂O

5. Select the nonpolar molecule.

1. H₂O
2. CH₃CH₂OH
3. HF
4. I₂

6. In this type of bonding, oppositely charged ions arrange themselves in an extended, tightly packed three-dimensional structure called a crystal lattice.

1. Polar covalent bonding
2. Nonpolar covalent bonding
3. Ionic bonding
4. Metallic bonding

7. In this type of bonding there are resulting net attrac¬tive forces from pairs of electrons that are shared between atoms.

1. Metallic bonding
2. Ionic bonding
3. Hydrogen bonding
4. Covalent bonding

8. In your own words, describe network covalent bonding.

Safety Precautions

All of the materials in this lab are nonhazardous and may be reused for future labs. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. On a plain 8½" x 11" sheet of paper, replicate the following figure with a #2 pencil. Make sure to darken it very well with the pencil.

2. Using the shared conductivity meter, flip the switch to the ON position and touch the electrodes to a darkened area in Figure 2. Make observations and take notes in the lab notebook.
3. Determine the positive and negative terminals on the red LED. The longer terminal on the LED is the positive terminal, and the shorter terminal is negative. With a permanent marker, make a small mark on the positive terminal. Bend or fold the terminals outwards as shown in Figure 3.

4. Make the LED contact with the drawing. Line up the negative terminal with the negative part in Figure 2. Do the same for the positive terminal. With a small amount of tape, secure each terminal down as seen in Figure 4.

5. Place a 9–V battery on the other side of the circuit. Line up the positive terminal of the battery to the positive terminal of the circuit. Do the same for the negative terminal of the battery.
6. In a darkened area of the room, observe the graphite circuit–powered LED.
7. Then attempt to redraw Figure 2 or a different version of Figure 2 with a smaller/thinner circuit, and attempt to draw it with a larger/thicker circuit. Do these changes affect the brightness of the LED?

Student Worksheet PDF

14152_Student1.pdf