Keep cutting a piece of wood in half. What is the smallest piece you could possibly end up with?
Wood is made up of different substances. The most abundant compound in it is cellulose, and cellulose is made of the elements carbon, hydrogen and oxygen, chemically combined. Each of those elements consists of atoms.
The word comes from the Greek atomos, meaning “cannot be cut” or “indivisible”.
Each element in the Periodic Table consists of only one type of atom. The element carbon, which partly makes up the cellulose in wood, consists of only carbon atoms.
An atom cannot be seen with the naked eye. The only way to get a feel for the scale is to count how many would fit along something familiar.
| Everyday object | How many atoms fit along it |
| A strand of human hair 0.001–0.006 cm across | A row of 1 million carbon atoms spans its diameter |
| A grain of rice about 0.5 cm long | A row of 50 million hydrogen atoms |
| A fingernail about 1 cm across | A row of over 100 million hydrogen atoms |
Even a caesium atom — one of the largest atoms we know of — is only about 0.000 000 007 cm across.
Nanoscale objects are tiny objects with sizes of less than 0.000 000 001 metre — one billionth of a metre. A strand of human DNA is about 0.000 000 002 5 m in diameter, so it is a nanoscale object.
Ordinary microscopes cannot see things that small. Scientists use special instruments — the atomic force microscope and the scanning tunnelling microscope.