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Properties of Common Molecular Substances (1 Favorite)

ACTIVITY in Polarity, Covalent Bonding, VSEPR Theory, Electronegativity, Lewis structures. Last updated May 22, 2019.


Summary

In this activity, students will apply their knowledge of molecular polarity, shape, and intermolecular forces to explain the differences in properties between different covalent substances.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

  • HS-PS1-1: Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
  • HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
  • Scientific and Engineering Practices:
    • Developing and Using Models
    • Analyzing and Interpreting Data

AP Chemistry Curriculum Framework

This activity supports the following learning objectives:

  • Big Idea 1: The chemical elements are fundamental building materials of matter, and all matter can be understood in terms of arrangements of atoms. These atoms retain their identity in chemical reactions.
    • 1.10 Students can justify with evidence the arrangement of the periodic table and can apply periodic properties to chemical reactivity.
    • 1.11 The student can analyze data, based on periodicity and the properties of binary compounds, to identify patterns and generate hypotheses related to the molecular design of compounds for which data are not supplied.
  • Big Idea 2: Chemical and physical properties of materials can be explained by the structure and the arrangement of atoms, ions, or molecules and the forces between them.
    • 2.1 Students can predict properties of substances based on their chemical formulas, and provide explanations of their properties based on particle views.
    • 2.11 The student is able to explain the trends in properties and/or predict properties of samples consisting of particles with no permanent dipole on the basis of London dispersion forces.
    • 2.13 The student is able to describe the relationships between the structural features of polar molecules and the forces of attraction between the particles.
    • 2.16 The student is able to explain the properties (phase, vapor pressure, viscosity, etc.) of small and large molecular compounds in terms of the strengths and types of intermolecular forces.

Objectives

By the end of this activity, students should be able to

  • Describe and understand a compound’s:
    • Name and chemical formula.
    • Intermolecular forces based on their structure and polarity.
    • Physical properties (i.e. melting/boiling point, solubility, and vapor pressure).
  • Draw a Lewis Structure including all bonding and nonbonding electrons
  • Determine the VSEPR shape with corresponding bond angle(s). NOTE: Do not have students identify shape name and bond angle for organic molecules.
  • Analyze the dipole moments to determine overall molecular polarity.
  • Contrast and compart the properties of two similar compounds based on their shape, polarity, and intermolecular forces.

Chemistry Topics

This activity supports students’ understanding of

  • Molecules and Bonding
  • Covalent Bonding
  • Lewis Structures
  • VSEPR Shapes
  • Electronegativity
  • Polarity
  • Valence Electrons

Time

Teacher Preparation: 10 - 15 minutes

Lesson: 45 minutes (one class period)

Materials

  • Student activity sheet
  • Optional: modeling kits

Safety

  • No specific safety precautions need to be observed for this project.

Teacher Notes

  • This activity can be used to reinforce student understanding of the relationship between molecular structure and properties, or may serve as a summative assessment on the topic.
  • A brief description of each substance has been given on the student activity sheet. You may choose to remove the description and have students conduct an online search of the common properties and uses of each.
  • If you have molecular modeling kits available, and the time to use them, have the students build models of each molecule before identifying the shape, polarity, and intermolecular forces of each. Students can also refer to the models when answering the questions asking them to compare and contrast the properties of similar molecules.
  • An Answer Key document is available for teacher reference. All images of molecular models are open sourced images from Wikimedia

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For the Student

Lesson

Directions:

  1. You may work individually or in a pairs to complete this activity.
  2. The following table contains the name and common use of 10 common compounds.
  3. For each of them fill in the empty columns: write the chemical formula, draw the Lewis Structure, draw and name the molecular shape using VSEPR theory and list all of the bond angels present in the molecule, identify all of the intermolecular forces (LD, DD, HB), and identify the molecule as polar (P) or nonpolar (NP).
  4. When the table is complete, use the information to answer the follow-up questions.
Ammonia is colorless gas that has a strong, suffocating odor. It is a common chemical compound that is used in fertilizers, and cleaners, and as a refrigerant.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Carbon dioxide is a gas at room temperature that is used during photosynthesis and is produced during hydrocarbon combustion, respiration, and fermentation



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Carbon tetrachloride is a colorless, sweet smelling liquid at room temperature. It is nonflammable and is commonly used in fire extinguishers.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Chloroform (trichloromethane) is a sweet-smelling, colorless liquid at room temperature. It is a strong anesthetic that was once referred to as the “knockout drug”.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Hydrogen sulfide is a colorless gas at room temperature. It has a foul odor similar to that of rotting eggs. It is produced in swamps, sewers, volcanos, and during digestion.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Isopropanol (2-Propanol) is a colorless, flammable liquid at room temperature. It is used in antiseptics and disinfectants, most commonly in hand sanitizers.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Nitrogen trifluoride, is a colorless, odorless gas at room temperature. In addition to being used in microelectronics, it is considered to be a strong greenhouse gas.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Ozone is a colorless, unstable gas at room temperature. It is present in the Earth’s “ozone layer” and helps shield the earth from the sun’s ultraviolet radiation.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Propane is a gas a room temperature. It is commonly used in home grills because it readily vaporizes from liquid to gas as it leaves the tank, making it easy to combust.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP
Water is a liquid at room temperature. It is thought that water is the only substance known to exist as a solid, liquid, and gas on the Earth’s surface.



Formula



Lewis Structure



Molecular Shape/Name/Bond Angels



IMFs



P/NP

Use the information from the table to answer the following questions about the properties of covalent substances. Be sure to include information about molecular shape, polarity, and intermolecular forces in your explanations.

Which substance would you predict to have a greater vapor pressure and a lower boiling point, ozone or carbon dioxide?
Why water is a liquid at room temperature and hydrogen sulfide a gas even though they are very similar in structure?
Explain why ammonia is 20 times more soluble than nitrogen trifluoride.
Why is the boiling point of propane (-42⁰C) so much lower than that of isopropyl alcohol (86⁰C)?
Explain why chloroform has a higher solubility and lower vapor pressure than carbon tetrachloride.