The Shrinking Ice Argument
Ice, water and steam are one substance. Ice keeps its shape, water pours into any shape, and steam spreads to fill a whole room.
If they are the same substance, where do such different properties come from?
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Science · Grade 8 Science
Chapter 1: Atoms and the Particle Model
Same particles, different arrangements.
Ice, water and steam are one substance. Ice keeps its shape, water pours into any shape, and steam spreads to fill a whole room.
If they are the same substance, where do such different properties come from?
Make your guess to turn the page.
Still to come: 10 pages · Words to Know · What We Learned · 4 questions · Explain It in Writing · Ask and Wonder
The idea this lesson is working on — Students imagine that particles take on the properties of the substance, so melting ice must soften or shrink its particles. The book takes that claim seriously, because 100 g of ice really does shrink from 109 mL to 100 mL on melting, then shows the same idea failing on steam. Ask: what would the particles have to do on boiling if Sam were right? The idea to reach is that only the arrangement and motion change.
Why ice is the exception — Water molecules in ice are held by hydrogen bonds in a hexagonal lattice with open space, so ice is about 9% less dense than liquid water. Most substances, such as wax or most metals, are denser as solids. Ice floating insulates lakes, which freeze from the top down.
About the numbers — Ice has a density of about 0.917 g per mL, so 100 g occupies about 109 mL and floats about 92% submerged in fresh water. Steam at 100 °C and normal pressure has a density of about 0.0006 g per mL, so 100 g occupies about 167 liters, roughly 1,700 times the liquid volume.