In a technical sense, the diameter of an atom doesn't really exist; we can draw an arbitrary line and say that the electrons in the atom are 90% (or 95%, or 99.999%, or whatever) likely to be found inside this boundary, but it doesn't really have a sharply defined diameter.
That said, Scanning Tunnelling Microscopes can measure the approximate diameters of individual atoms, and they aren't even that expensive as scientific instrumentation goes.
This determination is derived from other measurements; a direct measurement is not possible.
They can and have
Kind of... It is a measure of the electrons on a single atom of that element.
split the atom
split the atom
split the atom
This single atom remain an atom of krypton !
The scientist was John Dalton
Since the Earth is not a single atom, nor a collection of similar atoms, it does not have an atomic mass. Atomic mass is a measure of how much matter is contained by a specific atom.
Elements are not species. Helium is an element. Helium can be a single atom.
A compound can contain a single atom of gold, but a single atom of gold alone, by itself, cannot be a compound.
Rutherford
Rutherford.
No, a single atom is an element. Combinations of single atoms form compounds.