An electron and a proton are drinking in a bar.
Proton: “You know what? You’re really a negatively-charged particle.”
Electron: “Are you sure?”
Proton: “I’m positive.”
In the image above, representing an atom of Hydrogen (the most abundant material in the Universe), the dark nucleus (a single proton, usually) has been magnified about ten thousand times!
The diameter, measuring 1.1 A(ngstrom units) is not the limiting distance of the electron ‘cloud’ surrounding the proton (the cloud in this case being a single electron that is even smaller (by around 1/2000th) than the proton, which can appear at almost any point in the cloud volume). In theory the electron could be any distance from the proton, but the further out the less is the probability of it being located there at any given point in time.
The measurement of 1.1 Angstrom units ( 1 A = 1.0 x 10¯10 m ) is the average distance between the two proton nucleii of a molecule of H2 .
To give another perspective, if the greyed nucleus in the top picture was the actual size of the Hydrogen nucleus the electron would most likely be found somewhere within a sphere 50 m (164ft) in any direction from where you are sitting and would be the size of a needle tip! And this is the simplest and one of the smallest atoms we know of.
All matter is mostly, almost entirely, just empty space!