# How do scientists count the exact number of electrons, protons, neutrons in the atom? [duplicate]

An atom is very small so it is probably difficult to focus exactly on a single atom. I wonder how scientists count the exact number of electrons, protons, neutrons in an atom of a certain element.

Could you explain it?

In other words, how do we know that for example, $\ce{^{19}_9F}$ has nine protons and ten neutrons and nine electrons?