They are about one nanometer across. A nanometer is one-billionth of a meter. This is so small that it cannot be seen. The number of protons in the nucleus defines what type of element the atom will make. Gold atoms contain 79 protons.
Neutrons are neutral particles in the nucleus of the atom.
A normal gold atom has 117 neutrons. An atom of an element which has a different number of neutrons is called an isotope. A gold atom has 79 electrons which orbit in 6 shells. If the atom becomes charged by gaining or losing electrons, it is called an ion. Electrons are much smaller than protons and neutrons.