(c) Anthony K. Grafton 2003
How Big is an Atom?
Atoms are small. In fact, atoms are so small that it’s hard to imagine just how tiny they are. Think of it this way: atoms are so small that if you lined atoms up one after another, it would take about 1 million of them to stretch across the period at the end of this sentence.
Just in your own body, there are about 1 billion billion billion atoms (that’s a one followed by twenty-seven zeroes). That’s about 1 million times more than the number of stars in the entire Universe!
How do scientists deal with things that are so terribly small? Well, first, we need a new measuring stick. In our everyday lives we’re used to measuring things in inches, centimeters, feet, or meters. Our minds can handle thinking about something that’s 18 inches long, or something that’s 2.5 meters tall. But when the numbers in a measurement get very big or very small, our minds have a hard time grasping what they mean. So when scientists talk about atoms, they usually talk about measuring their size in units of “angstroms”.
There are 10 billion angstroms in one meter. Scientists use the angstrom as a unit of measure because most atoms are just a few angstroms wide. It’s much easier to talk about the size of an atom by saying its 3 angstroms wide rather than saying its 3 ten-billionths of a meter across.
Like most measurement units, the word “angstrom” is often abbreviated. The correct way to abbreviate angstrom is with a capital “A” with a small circle on the top like this: Å.
The angstrom unit gets its name from a 19thcentury Swedish physicist named Anders Jonas Ångström. Professor Ångström is regarded as one of the fathers of modern spectroscopy. Spectroscopy means studying how light and matter interact with each other. The experiments that Ångström performed help lay the foundations for our modern understanding of the structure of atoms.
Can you think of some things that are so large that we have to come up with new units to grasp their sizes? Can you look up the definition of an “astronomical unit” (an AU)? How about a light-year? Or a parsec? Or a “mole”?