Chapter 1. Chemical Bonds

1.1 Teacher Tools

Key Ideas: Atoms are held together in substances by bonds. These bonds are attractions between valence electrons and the nuclei of other atoms. There are four basic types of bonds between atoms: ionic bonds, molecular covalent bonds, metallic bonds, and covalent network bonds. Most of the substances in our everyday lives can be classified into one of these four categories of bonding based on their elemental makeup and on their properties. Valence electrons are distributed differently within a substance depending on the type of bonding that is present. Differences in the way the valence electrons are distributed help to explain differences in the properties of substances.

Key Terms: dissolve, soluble, insoluble, conductivity, chemical bond, ionic bond, metallic bond, covalent bond, molecular covalent bond

1.2 Teacher Tools

As a result of this lesson, students will be able to:

• Classify substances into four categories based on the properties of solubility and conductivity.
• Describe the atomic makeup of substances based on whether or not they are soluble or conduct electricity.
• Define a chemical bond and describe the four basic types of chemical bonds
• Use chemical formulas to sort substances into bonding categories.
• Predict the properties of a substance based on its chemical formula and bonding type.

Focus on Understanding

• Every time a new model or graphic representation is introduced, there is room for visual misinterpretation of that model. Assist students in making sense of models.
• Students may have trouble grasping what a molecular unit is, and that molecules do not break apart into individual atoms when they dissolve.
• Elemental substances can prove confusing for students. While all elemental substances are made up of just one kind of atom, some elements, like oxygen, O₂, are never found as single atoms.

1.3 Teacher Tools

What Takes Place: What Takes Place: A key goal of the lesson is for students to understand how to classify substances according to the type of bonding and to relate the type of bonding to the properties of substances.

The atomic level focus is on drawings of four models of bonding: ionic, covalent network, metallic, and molecular covalent bonding. Students match these to a variety of substances, their chemical formulas, and some basic properties.

The macroscopic focus is on an experiment to measure the conductivity and solubility of various substances, and the solution conductivity for those substances that dissolve in water. Students will examine patterns in the data and be able to sort the substances into four categories.

The symbolic focus is on chemical formulas and how these give glues as to the type of bonding and the macroscopic properties of a substances.

1.4 Teacher Tools

Materials:

• Distilled water
• Stirring rod
• paper clips (2 per beaker)
• 100 mL beakers (2 for each substance to be tested)
• Conductivity tester

Substances to be tested:

• water, H₂O
• aluminum, Al
• sucrose, C₁₂H₂₂O₁₁
• sodium chloride, NaCl
• silicon dioxide, SiO₂
• polyethlyene,[CH₂]_n
• ethanol, C₂H₆O
• copper, Cu
• calcium chloride, CaCl₂
• gold, Au
• copper (II) sulfate, CuSO₄

Safety: Safety goggles must be worn at all times.

Setup: For each substance to be tested, set up two beakers: one for the pure substance (dry) and one for the pure substance mixed with distilled water. Use a conductivity tester to measure the conductivity of the dry materials and the mixtures. If you do not have a conductivity tester, you can make one from a string of holiday lights as the source of bulbs and wire, a 9-volt battery and a battery snap connector.

Cleanup: Evaporate water from test materials so they can be stored for future use. If necessary, follow your local guidelines for disposal.