Part 1: Engage (Anchoring Phenomenon)

Table salt (NaCl) melts at a scorching 801°C, while table sugar (sucrose) melts at just 186°C. Even more surprisingly, solid carbon dioxide (dry ice) doesn’t even melt at room temperature—it sublimates directly into a gas at -78.5°C.

1. Observations and Questions:

• Why do different solid substances require vastly different amounts of thermal energy to change state?
• Generate at least two “need to know” questions about the internal structure of these substances.

Part 2: Explore (Simulation Investigation)

Open the Crystal Lattice Flythrough simulation.

2. Data Collection:

• Select different types of crystalline structures in the simulator (e.g., ionic crystals like NaCl, covalent network crystals like diamond, or molecular crystals like ice).
• Fly through the lattice structures. What do you notice about the arrangement of particles (atoms, ions, or molecules) in each type?
• Observe the “bonds” or interactions holding the particles together in the simulation. How do the connections in an ionic lattice differ visually or conceptually from those in a molecular solid?
• Record the bulk properties (if provided by the simulation or your prior knowledge, such as melting point) for each substance you observe.

Part 3: Explain (Sensemaking)

3. Connecting Structure and Forces:

• Based on your observations, what holds the particles together in a solid lattice?
• How does the structure of the substance at the bulk scale (e.g., a repeating 3D grid of alternating positive and negative ions) relate to the electrical forces between the particles?
• When a substance melts, the particles move further apart and slide past one another. How does thermal (kinetic) energy affect the ability of the electrical attractions to keep the particles locked in their lattice positions?

4. Inferring Strength:

• If salt requires 801°C of thermal energy to disrupt its lattice, but sugar only requires 186°C, what can you infer about the relative strength of the electrical forces holding salt ions together compared to the forces holding sugar molecules together?

Part 4: Elaborate/Evaluate (Argumentation & Modeling)

5. Planning an Investigation: You have observed the structures of different crystals in the simulation. Now, plan an investigation to gather evidence to compare the structure of unknown substances at the bulk scale to infer the strength of their internal electrical forces.

• Identify the Evidence: What bulk properties will you measure (e.g., melting point, boiling point, volatility)?
• Procedure: Describe how you will collect this data (e.g., heating samples on a hot plate and recording the temperature at which they melt).
• Reasoning: Explain why comparing these specific macroscopic bulk properties will provide evidence about the invisible, microscopic electrical forces between the particles. Be sure to use the concept of thermal energy overcoming attractive forces in your explanation.