Question

Why is there an atomic mass unit?

Answer 1

Why? Because atoms have definite and measurable masses....

Explanation:

We could report atomic masses with units of grams or kilograms. And thus an `""^1H` atom has a mass of `1.67xx10^-24 *kg` or `1.67xx10^-21 *g`. This is a bit inutile given that the we have to go thru the rigmarole of exponents, and even here they are a pain to write down and format....

Historically, while the mass of an hydrogen atom could not be experimentally measured … its mass could be inferred by reference to the mass of other atoms and molecules... and historically `1*"amu"` was `1/12*"th"` the mass of the `""^12C` `"isotope.."`