Question

Why do we use prefixes like nano, pico, kilo, and micro?

Answer 1

For convenience... We would not want to write

`"0.000000001 m"`

to express one billionth of a meter. That just doesn't look nice, and it is preferable to write

`"1 nm"`,

1 nanometer, as there are `10^9` nanometers in one meter; they are one billionth of a meter in physical size. Of course, we could also have, in scientific notation, written

`10^(-9) "m"`,

which is OK, but as chemists, we prefer to have our numbers be roughly between `0.01` and `100`, and for them to be standardized (be made common usage) among us. They tend to be dependent on context.

One tends to use `"nm"` to describe UV and visible wavelengths, i.e. `"400 - 700 nm"` describes the visible range of light. We'd rather not say `4.00 xx 10^(-7) "m" - 7.00 xx 10^(-7) "m"`, which is awkward.

Common uses:

• `"nm"`: wavelengths of visible light
• `"pm"`: bond length, atomic radii
• `"km"`: driving distances
• `mu"m"`: bacteria size