1. Covalent Bonds Lesson Plan (three class periods)
Learning objectives
Students will be able to:
- Write the correct chemical formula for different covalent compounds
- Use the electron dot diagrams to show the formation of single, double and triple covalent bonds
- Describe and give examples of compounds with molecules made by covalent bonds
Materials and teacher-developed resources
Paper (Student Notebook), pencils, software (ActivInspire/Promethean)
Learning activities
The teacher will review the concepts of ionic and molecular compounds, emphasizing the differences between the two. Students will be reminded the definitions of molecule and molecular compound. Molecular compounds are composed of molecules and almost always contain only nonmetals. Molecular compounds form covalent bonds. Non-metals hold onto their valence electrons. They cannot give away electrons to bond, but still want noble gas configuration and get it by sharing valence electrons with each other. (Octet rule still applies.)
The teacher will explain that single covalent bonds form by sharing a pair of valence electrons. Bonds that involve two shared pairs of electrons are called double covalent bonds and bonds that involve three shared pairs of electrons are called triple covalent bonds. Students will draw Lewis structures of molecules with single covalent bonds (fluorine, chlorine, bromine, iodine, hydrogen, water, ammonia, methane), double covalent bonds (oxygen, carbon dioxide, ethene) and triple covalent bonds (nitrogen, acetylene carbon monoxide).
The teacher will emphasize that carbon, nitrogen, oxygen, fluorine, chlorine, bromine and iodine are atoms contain unshared pairs of electrons (also called lone pairs or nonbonding pairs). The teacher will show on the board the completion of orbitals 2p with electrons. Students will note that the chemical formulas for ionic compounds describe formula units, while chemical formulas for covalent compounds describe molecules. The teacher will also emphasize that ionic compounds are not composed of molecules and there are no single units of an ionic compound, while individual molecules actually do exist.
The students will be asked to write the correct Lewis dot diagrams and structural formulas for several compounds. They will be provided with pairs of elements and will be asked to select the pairs that are likely to form molecular compounds with a single covalent bond.
2. The Carbon Dioxide Lesson Plan (one class period)
Learning Objectives
Students will be able to:
- understand how do molecules of CO2 gas interact with electromagnetic radiation
- explain the molecular structure of carbon dioxide and how it bends that make it able to absorb energy
- explain the greenhouse effect of Earth’s atmosphere
Materials & Teacher-developed Resources
Student handouts, pencils, textbooks, Carbon Cycle Interactive Lab Simulation software
Learning Activities:
The teacher will explain that molecules of carbon dioxide (CO2) can absorb energy from infrared (IR) radiation. Students will watch a simulation that shows a molecule of CO2 absorbing an incoming infrared photon. The energy from the photon causes the CO2 molecule to vibrate. Sometime later, the molecule gives up this extra energy by emitting another infrared photon. Once the extra energy has been removed by the emitted photon, the carbon dioxide molecule stops vibrating.
Molecules are constantly in motion, colliding with other gas molecules and transferring energy from one molecule to another during collisions. In the more-complex, real-world process, a CO2 molecule would most likely bump into several other gas molecules before re-emitting the infrared photon. The CO2 molecule might transfer the energy it gained from the absorbed photon to another molecule, adding speed to that molecule's motion. Since the temperature of a gas is a measure of the speed of the molecules in the gas, the faster motion of a molecule that eventually results from the IR photon that was absorbed by a CO2 molecule raises the temperature of the gases in the atmosphere.
3. Methane, The Simplest Organic Compound Lesson Plan (one class period)
Learning Objectives
Students will be able to:
- understand the molecular structure of methane
- explain the geometry of methane molecule
- explain the role of methane as greenhouse gas
Materials & Teacher-developed Resources
Student handouts, pencils, textbooks, Methane Structure Interactive Lab Simulation software
Learning Activities:
The teacher will ask students what do the gases of decomposing plants, natural gas, and the atmosphere of Saturn's moon, Titan, all have in common? The answer is they all contain methane. The teacher will explain that methane is a colorless, odorless, highly flammable gas at room temperature and can be found in a wide variety of sources on Earth. On Earth, methane can be found as a major component of natural gas that is stored in the earth's crust. Methane is also a common by-product of the decomposition of biological matter, such as decaying plants or animals.
Methane is classified as an organic compound, a substance composed of mainly carbon and hydrogen or a hydrocarbon. With a formula of CH4, that is, four hydrogen atoms bonded to a single carbon atom, methane is the simplest of the hydrocarbons, a group also referred to as the alkanes.
The students will learn that chemical bonds found within methane are single covalent bonds.
For methane the covalent bonds form from the sharing of a single electron from each hydrogen with the four unpaired valence electrons of a single carbon atom. The teacher will explain that hydrogen atoms are arranged around the central carbon atom in a geometry known as a tetrahedral geometry.
Even though methane is involved in a wide variety of reactions, two reactions in particular are of fundamental importance, combustion and halogenation. Combustion of methane by industrial sources or when mixed with other hydrocarbons in natural gas is used extensively within industry to generate electrical power and within homes to generate heat. Halogenation involves the addition of a halogen, one of the elements found in Group 17 of the periodic table, to produce compounds known as methyl halides. The products of halogenation are used in the production of everything from plastics to pharmaceuticals.
4. Nitrous Oxide, The Laughing Gas Lesson Plan (one class period)
Learning Objectives
Students will be able to:
- understand the molecular structure of nitrous oxide
- explain the geometry of nitrous oxide molecule
- explain the role of nitrous oxide as greenhouse gas
Materials & Teacher-developed Resources
Student handouts, pencils, textbooks, The Greenhouse Effect Lab Simulation software
Learning Activities:
The teacher will explain that nitrous oxide or dinitrogen oxide, is a colorless, sweet tasting, non-flammable gas at room temperature and is known as “the laughing gas”. Continued breathing of the vapors may impair the decision making process. Although it is non-flammable, nitrous oxide will accelerate the burning of combustible material in a fire, due to the increase of available oxygen.
Students will learn that nitrous oxide is soluble in water and its vapors are heavier than air. It is used as an anesthetic, in pressure packaging, and to manufacture other chemicals.
Students will draw the Lewis structure of nitrous oxide, that is N+=N- =O.
Then, the teacher will present a simplified diagram to explain the nitrogen cycle in agricultural practices and the resultant emission of nitrous oxide (N2O) by the application of nitrogen fertilizers.
Students will discuss the role of microbes in the nitrogen cycle and how the bacterial actions on nitrogen-based fertilizers (added to the soil) can cause the emission of nitrous oxide (N2O) into the atmosphere.
Then, they will watch a video clip that presents the best management practices (BMPs) to mitigate the adverse effects of fertilizer use on global warming.
5. Global Warming Potential Lesson Plan (two class periods)
Learning Objectives
Students will be able to:
- define the greenhouse effect
- explain which are the greenhouse gases and how do they contribute to global warming
- define the Global Warming Potential
- predict some of the effects of global warming on the climate
Materials & Teacher-developed Resources
Student handouts, pencils, textbooks, The Greenhouse Effect Lab Simulation software
Learning Activities:
The teacher will start the lesson by asking students to write and share their opinions about the influence of human activity on Earth’s climate for the past 100 years. Then, the teacher will introduce the concept of greenhouse effect and its influence on global warming of Earth.
Next, the teacher will list the five main greenhouse gases (carbon dioxide, methane, nitrous oxide, chlorofluorocarbons and water vapor) and how do they contribute to global warming (have the students watch the PBS video called “Global Warming: The Physics of the Greenhouse Effect”).
On the next section, the teacher will introduce the concepts of lifetime - how long a gas stays in the atmosphere - and Global Warming Potential (GWP). The teacher will explain the reason the GWP was developed by the scientific community - to allow comparisons of the global warming impacts of different gases.
Students will discuss the actions that humans and policy makers should take to address the global warming issue and to slow the climate change.
