Module 2 Intro

Module 2—Chemical Compounds

Read

Molecular Compounds

You have seen how molecular elements are formed through the sharing of electrons. The same principles can be used to explain the bonding of different non-metallic atoms. Read “Molecular Compounds” on pages 86 and 87 of your textbook.

From your reading you should be able to explain how the bonding capacity of an atom can be determined from its Lewis diagram. Can you explain how bonding capacity of the atoms involved in a compound will determine the chemical formula for the compound?

Try This

TR 2. Copy into your notebook “Table 1: Bonding Capacities of Some Common Atoms” on page 87 of your textbook. Add rows to your table to provide information for these elements: phosphorous, sulfur, and silicon.

TR 3. Use the information that you just read in the textbook to help you to write steps that describe how to draw Lewis formulas for molecular compounds. Provide an example in your description for a molecular compound. Use examples other than water (H2O) or carbon dioxide (CO2).

Watch and Listen

Watch the animation of the preparation of a Lewis formula for carbon dioxide. Use the animation to check the accuracy of the instructions you wrote.

Example

Draw the Lewis diagram and structural diagram for CH2O, commonly called formaldehyde.

Submit your answers to TR 2. and TR 3. to your teacher for feedback.

In Chemistry 20 the discussion of molecular bonding is limited to valence electrons and the assumption that all electrons must be paired. In reality, there are compounds that violate these assumptions, but you are not required to study these exceptions in Chemistry 20.

Self-Check

SC 7. Draw the Lewis formulas and structural diagrams for the following compounds:

            hydrogen chloride (HCl)
            methane (CH4)
            hydrogen peroxide (H2O2)
            methanol (CH2O)

Self-Check Answers

 

SC 7.

 

hydrogen chloride

 

 

methane

 

 

hydrogen peroxide

 

methanol

 

Watch and Listen

Ionic Compounds

Recall from your work in Module 1 that the formation of an ionic compound is a result of the collision between a metal atom and a non-metal atom. This collision results in a transfer of electrons, forming positive and negative ions that have filled energy levels. This transfer is due largely to the difference in electronegativity between the metal and non-metal atoms. The formation of ionic compounds can be represented using Lewis symbols as well. For example, the formation of sodium fluoride can be written as follows:

The formation of an ionic compound, like sodium fluoride, involves a loss of electrons by a metal and a gain of electrons by a non-metal.

The following animation will allow you to see the formation of sodium chloride and magnesium sulfide using Lewis symbols. Notice that magnesium sulfide is MgS rather than Mg2S2. Remember that ionic compounds are referred to by their simplest number ratio.