The difference between atoms, ions and isotopes is the number of subatomic particles. An atom is the basic building block of matter, the smallest molecule of an element that exists and that cannot be chemically divided by ordinary means. Each atom is comprised of protons, neutrons and electrons. In ions, the number of electrons differs, and in isotopes, the number of neutrons varies.
According to Visionlearning.com, a typical atom has no electrical charge because the number of positively charged protons is the same as the number of negatively charged electrons. The number of electrons in an atom can change, though, either by gaining additional electrons from other atoms or by giving away one or more of its electrons to nearby atoms. When an atom's number of electrons changes, the atom carries an electrical charge. This electrically charged atom is referred to as an ion.
Typically, an atom has the same number of protons and neutrons. Some atoms gain or lose a neutron. When the number of neutrons in an atom changes, an isotope is formed. Isotopes of an atom have different atomic masses and exhibit different properties, but they are still the same element.
An element's atoms always have the same number of protons.