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

Aug 14, 2017

For convenience... We would not want to write

$\text{0.000000001 m}$

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

$\text{1 nm}$,

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

${10}^{- 9} \text{m}$,

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 $\text{nm}$ to describe UV and visible wavelengths, i.e. $\text{400 - 700 nm}$ describes the visible range of light. We'd rather not say $4.00 \times {10}^{- 7} \text{m" - 7.00 xx 10^(-7) "m}$, which is awkward.

Common uses:

• $\text{nm}$: wavelengths of visible light
• $\text{pm}$: bond length, atomic radii
• $\text{km}$: driving distances
• $\mu \text{m}$: bacteria size