Chapter 4 · Atoms and Elements
4.1Experiencing the Atoms at Tiburon
7 min · two checks
Predict
If atoms are too small to see, what kind of evidence can still show they are there?
The idea
- Explain what it means to observe atoms indirectly.
- Connect a macroscopic sample to an enormous number of atoms.
You will not see an atom with a classroom microscope the way you see a cell. Atoms are about 10⁻¹⁰ m across. What you can see is the consequence of huge numbers of them acting together, and, with modern instruments, a map of a surface built by dragging a fine tip across it and recording the force. Those images are evidence, not photographs in the ordinary sense. They agree with the same atomic model that explains mass ratios in compounds.
A spec of dust already contains more atoms than you could count in a lifetime. That scale is why chemists count by the mole later, and why a chemical equation describes enormous collections even though it is written with a few symbols. The rest of this chapter builds the particle those instruments and those mass ratios are pointing at.
Keep these
- Atomic size is on the order of 0.1 nm.
- Most evidence for atoms is indirect and still decisive.
- Visible samples contain unimaginably many atoms.