7.1 What Is Matter Made Of?
Probe and Ponder
Pick up sand on a riverbank and you are holding the end of a long story. In the mountains, rocks slowly break apart; rivers tumble the pieces along, grinding them down into pebbles, then sand, then fine clay. But is a grain of sand the smallest piece a rock can become — or can it be broken down still further?
Activity 7.1 — Breaking down chalk Snap a stick of chalk in two, again and again, until you can’t break it by hand. Then grind the bits with a mortar and pestle into a fine powder and look at it through a magnifying glass. Every tiny grain is still chalk — grinding only made the pieces smaller (a physical change), it did not turn the chalk into anything new.
Now imagine grinding on and on. Eventually you would reach pieces that simply cannot be broken any further. These ultimate tiny units are the building blocks the chalk was made of.
Constituent Particles A whole piece of chalk is built from a huge number of tiny units called its constituent particles — the basic units that make up a larger piece of a substance. The same is true of sand, clay, and everything else. Matter is made of enormous numbers of these particles, far too small to see even with an ordinary microscope.
Where does the sugar go?
Activity 7.2 — Dissolving sugar Add sugar to a glass of water without stirring and taste the top — not sweet yet. Now stir until the sugar disappears completely, and taste the top again — sweet! The sugar is clearly still there (you can taste it), yet you can’t see a single grain. Where did it go?
When sugar dissolves, it breaks up into its constituent particles (each grain holding millions upon millions of them), which spread out and slip into the gaps between the water particles.
Interparticle Spaces There are tiny gaps between the particles of matter, called interparticle spaces. The dissolved sugar particles tuck themselves into the spaces between the water particles — which is exactly why the sugar “vanishes” yet the water tastes sweet throughout.
Our Scientific Heritage: Acharya Kanad The idea that matter is made of tiny indivisible units is ancient. The Indian philosopher Acharya Kanad spoke of the Parmanu (atom) — tiny, indivisible, eternal particles he believed all matter was made of — writing about them in his Vaisheshika Sutras, thousands of years ago.