The space surrounding the nucleus is occupied by the electrons, moving so rapidly that we can think of them as being everywhere at once. (Note: This is not very accurate, but it will suffice for now.)
An electron is not part of the atomic nucleus, but orbits the nucleus. It carries a unit-negative electric charge (i.e. -1.60 x 10-19 C). An electron is nearly mass-less. It has a rest mass of 9.11 x 10-31 kg. The rest mass of a proton is 1836 times the rest mass of an electron.
In a neutral atom, the number of electrons is the same as the number of protons. Circulating electrons are held in orbit by the influence of protons’ positive charge.
Do you know?
The electron has an anti-matter counterpart called the positron. This anti-particle has precisely the same mass, but it carries a positive charge. If it meets an electron, both are annihilated in a burst of energy.
The hydrogen nucleus is unique in having no neutron, only a single proton.