When an atom gains or loses an electron, it is called an ion. A positive ion is formed when an atom loses an electron (negative charge) because it will have more protons than elecrons.
A negative ion is formed when an atom gains an electron (negative charge) because it will have more electrons than protons.
In the nucleus of an atom, there are two type of particles namely protons and neutrons. Protons are particles which have a positive charge while neutrons have no charge, they are neutral.
In orbit around the nucleus are the electrons. These are found in a series of orbits (depending on the atom) with differing number of electrons.
The atomic number of an atom is given by the number of protons in the atom, while the atomic mass is given by number of neutrons plus number of protons.
The number of the electrons of each atom is the same as the number of protons in its nucleus.