Concepts explained
Is There an End to Cutting? Finding Grains No One Could See
Cut a sheet of paper in half, and in half again — is there an end? For two thousand years 'no' won. Then, in an age when nobody had seen an atom, a scale showed something that only atoms could explain.
One said there is an end, one said there is not
A man in ancient Greece said there is an end: grains that cannot be cut further, with everything in the world made of those grains gathered this way and that. He called them by a word meaning 'uncuttable': .
But there was no evidence, only the thought. A more famous philosopher of the same age said the opposite — matter can be divided without end. People believed the famous one, and the atom was forgotten for two thousand years.
The scale gave numbers with gaps in them
Piece one said chemistry began with a scale. Again, a scale.
Around 1800 an English schoolteacher carefully weighed how substances combine. To make water you need hydrogen and oxygen, and by weight the ratio was always 1 to 8. Never 1 to 7, never 1 to 9. Only that ratio.
Stranger still: carbon and oxygen join to make gas, and two different gases come out. The oxygen in one weighed exactly twice the oxygen in the other. Not 1.5 times, not 1.7 — exactly two.
Think of building bricks. Build something out of bricks and the weight goes up one brick at a time, in steps. There is no half-brick weight. Matter behaved like that.
Saying something exists that no one has seen
He never saw an atom. There was no way to. Yet on the scale was something that only atoms could explain. The two-thousand-year-old idea came back — this time with evidence attached.
Piece one's candle looks different now. The candle 'joining' oxygen means the candle's grains and the air's grains come apart and join up again in new pairs. Not one grain is lost. That is why the weight stays the same.
A little further in
Is the atom really uncuttable?
Its name means 'uncuttable', and about a century later it was cut. Smaller things were found inside — electrons, and a nucleus at the centre. The name stayed; the meaning moved.
Even so, for chemistry the atom is still the right grain. While candles burn, iron rusts and food is digested, atoms only swap partners; they do not break. Breaking atoms is not chemistry — it is what happens in nuclear plants and inside stars.
So grains exist. Then how many kinds are there? Hydrogen, oxygen, carbon, iron… any number at all, or is there a rule? The next piece lays the kinds out in a row. Lay them out, and a pattern appears.
The question that remainsBelieving in atoms when no one had seen one turned out to be right. What separates the times it is right to believe in the unseen from the times it is not?