Purpose of the discussion

The purpose of the discussion is for students to clarify their understanding of transformation of solid ice to liquid water at the particle level. Focus the discussion on the investigation question: What changes and what stays the same as ice melts?

Engage students in the focus question

Imagine a tray of ice cubes. Imagine those cubes melting. If we could zoom in and see the ice melt at the particle level - like we did with the Particle Magnifier - what do you think would change and what would stay the same as ice melts?

• The individual particles stay the same when ice melts.
• For both ice and water, the warmer the temperature, the more the particles move.
• In ice, the particles are arranged in a pattern, even when they are warmed up and vibrating (jiggling but still in place).
• In water, individual particles slide around and collide, and are not arranged in a pattern.

Revisit the Particle Magnifier (Water)

What connections do you notice between the visible evidence and changes at the microscopic level?

Visible Level	Particle Level
Solid water (ice) keeps its shape and liquid water doesn't.	Particles in ice are held in a shape. Particles in water aren't locked in place. They slide past and collide with one another.
At the visible level, reasoning tells us that water remains the same - ice is formed from water and returns to water when it melts.	Particles in the model remain the same. Particle motion and arrangement change.

Summarize the discussion and recap the investigation

When a sample of water is transformed to ice and back to water, the weight does not change. When water freezes, the volume increases but returns to the original volume when the ice melts. The particle model of matter explains these transformations of water.