Particulate Nature of Matter · Lesson 4 of 6
Spaces Between Particles
“Investigate why air compresses easily and why dissolved substances can fit among water particles.”
• Compare relative interparticle spaces in solids, liquids, and gases. • Explain syringe observations for trapped air and water. • Interpret changing levels when sugar dissolves in water. • Distinguish soluble particles from insoluble sand and visible dust. • Avoid treating interparticle spaces as air-filled holes.
Can the particles be pushed closer?
Pull out the plunger of a needle-free syringe, cover its opening with a thumb, and push the plunger inward. The trapped air occupies less volume. If you stop pressing, the plunger tends to move back. The observation suggests that gas particles have substantial space between them and can be brought closer by pressure.
Try the comparison with a syringe filled with water and with no trapped air. The plunger hardly moves. Liquid particles are already much closer than gas particles, so water is practically incompressible under this simple test. “Practically” matters: the activity is about the very different amounts of compression we can observe.
The ability of a material to decrease its volume when pressure pushes its particles closer together.
Problem
Why does a pushed syringe plunger move outward when you stop pushing it, provided the opening stays blocked?
- 1.Pushing has brought the trapped air particles closer.
- 2.The compressed gas presses outward and tends to expand when the extra push is removed.
- 3.The particles spread through more of the available space, moving the plunger outward.
Where does dissolved sugar fit?
Mark the level of water in a glass as A, add sugar and mark the raised level as B, then stir until the sugar dissolves and mark the final level as C. The level may fall from B after dissolution. The final solution’s volume is less than the simple sum of the separate water and sugar volumes. One useful particle explanation is that dissolved sugar particles occupy spaces among water particles.
The drop from B to C is an observation, not proof that the sugar has ceased to exist. The solution still contains it. The result need not mean the level returns exactly to A: the added sugar still contributes to the final mixture. Mark carefully and do not infer that every mixture must give exactly the same level change.
Problem
A vessel has water at A. Sugar raises the level to B before stirring. After complete dissolution, C lies below B. What can you conclude?
- 1.The visibly added sugar occupied space before it dissolved.
- 2.After its particles spread among water particles, the combined volume can be less than the sum of the starting volumes.
- 3.The sugar remains in the solution even though its grains are invisible.
Why sand behaves differently
Try comparing soluble sugar, common salt, or glucose with insoluble sand or small stone pieces. Sand does not dissolve in water. Its grains settle and occupy space in the vessel, making the total level rise. Spaces between water particles do not imply that every added solid will dissolve: whether the water can separate and disperse a substance’s particles also matters.
Problem
Both are solids. Why can sugar disappear from sight on stirring in water while sand does not?
- 1.Water can separate and disperse sugar’s constituent particles in this situation.
- 2.It cannot similarly pull apart the constituent particles of sand.
- 3.Sand remains as visible grains that settle; sugar remains present as dispersed particles.
The spacing across three states
Solids generally have the smallest spaces, liquids have somewhat more room for their particles to move, and gases have much larger spaces. Solids still have interparticle spaces despite close packing. Those microscopic spaces are not pockets filled with air; in the model there is nothing in between. Remember the special case of ice, which is more spread out than liquid water.
| State | General spacing | Response to a push | Useful observation |
|---|---|---|---|
| Solid | Smallest in the general comparison | Difficult to compress | Keeps a definite shape |
| Liquid | A little more than solid | Practically incompressible in the syringe test | Keeps a definite volume |
| Gas | Largest | Compresses noticeably | Fills its container |
Suspended particulate matter in polluted air means tiny dust or smoke particles. Each dust grain contains enormous numbers of the much smaller constituent particles of matter. Do not draw a one-to-one match between the two scales.
“More spacing” is a general model for ordinary solids, liquids, and gases. Ice is an exception to the simple solid-versus-liquid spacing rule. Solubility also cannot be decided from spacing alone.
Problem
A student says that air must fill every space between particles of an iron nail. How would you respond?
- 1.The particles in the iron are very closely packed with small spaces between them.
- 2.These interparticle spaces are not tiny air bubbles.
- 3.The model describes empty space between the constituent particles.
Quiz
What happens to trapped air in a closed syringe when the plunger is pushed?
Why is water much harder to compress than air in the syringe test?
What can a fall from level B to C after sugar dissolves indicate?
Why does sand settle rather than make a clear solution like sugar?
What fills interparticle spaces in a solid according to this model?
Practice Problems
- Sketch the trapped-air syringe before and after pushing the plunger, keeping the number of drawn particles the same.
- Explain why a water-filled syringe with no air inside is harder to compress than an air-filled one.
- Describe levels A, B, and C in the sugar-and-water activity. What does a level below B suggest?
- Predict what happens when sand rather than sugar is added and stirred into water. Explain the level and visibility.
- Compare the spacing of a gas, a liquid, and an ordinary solid. State the ice exception.
- Correct the claim, “The spaces inside an iron nail must contain air.”
- Explain why dust floating in air and an air constituent particle are not the same kind of object.
Key Takeaways
• Gas particles have large spaces between them, so trapped gas can be compressed. • Liquid water is practically incompressible in the syringe comparison. • A dissolved substance can be present even when its grains are no longer visible. • Sand remains insoluble and settles; spacing alone does not guarantee dissolution. • Interparticle spaces are not air-filled, and dust grains contain many constituent particles.