HS-PS1-3 Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
Clarification Statement: Emphasis is on understanding the strengths of forces between particles, not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.
Assessment Boundary: Assessment does not include Raoult’s law calculations of vapor pressure.
This resource is explicitly designed to build towards this performance expectation.
Comments about Including the Performance Expectation
The molecule models allows for students to compare forces between particles of different molecules, water, ethane, and ethanol. The water molecules in the model kit contain magnets to simulate their polarity while the ethane molecules do not contain magnets and the ethanol molecules are only magnetic on the end with the –OH functional group. In this way, students will investigate how the difference in the electrical forces between particles in these substances causes differences in their properties.
The initial exploration outlined in this lesson could be extended to include wet lab work designed to compare the surface tension properties of water to other substances in the liquid state (alkanes or alcohols). This would help students connect the investigation with observations of a wider range of bulk scale properties, not just water. The wet lab work would be best completed before the work with the 3-D models, but could also be done during the work with the molecules or afterwards.
It is important that before students investigate surface tension (or other properties) with these molecule kits the teacher emphasize differences in magnetic forces between the molecule models and electrical forces between actual molecules. Suggestions for explaining this difference to students are provided on pages 5-7 of the lesson guidelines.