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Atoms

Radiation and the atom · level 3, lesson 1 of 6

A question to start

Cut a piece of gold foil in half, then in half again, and again. Could you go on for ever?

The idea

No. In the end you would reach the smallest piece that is still gold: an atom of gold. Everything is made of atoms.

Atoms are unbelievably small. An atom is about a ten-millionth of a millimetre across. About a million atoms side by side would stretch across the width of one human hair. A single drop of water holds thousands of billions of billions of atoms.

The idea that things are made of tiny pieces that cannot be cut is old. Thinkers in ancient India and ancient Greece both wrote about it more than two thousand years ago. Only in the last two hundred years have scientists shown that atoms are real.

one haira million atoms across it

Worked examples

1. A hair. A hair is about 0.1 mm wide. An atom is about 0.000 000 1 mm. So \(0.1 \div 0.0000001 = 1{,}000{,}000\) atoms fit across it.

2. A grain of sand. A grain of sand is about 1 mm across: about ten million atoms from side to side.

3. Gold leaf. Gold can be beaten into leaf so thin that light shines through it, yet it is still hundreds of atoms thick.

Try it

  1. What is an atom?
  2. About how many atoms fit across a hair?
  3. Can you see an atom with a magnifying glass?
  4. Who first wrote about tiny uncuttable pieces?
Answers
  1. The smallest piece of an element that is still that element.
  2. About a million.
  3. No, atoms are far too small.
  4. Thinkers in ancient India and ancient Greece, more than two thousand years ago.

Common mistake

"Atoms are like grains of sand." A sand grain holds an enormous number of atoms. Atoms are smaller than anything a microscope that uses light can show.

Where it leads