Matter is made up of “grains” called atoms. At the center of the atom are particles called protons and neutrons. What differentiates them is their mass and their electrical charge: a proton is a little lighter and more positive charge while a neutron is a little heavier and neutral charge (ie to say that it has no electric charge!). Around this set called nucleus, small, very light and negatively charged elements turn : the electrons.
It is the number of protons that makes it possible to say whether one is dealing with hydrogen, oxygen, calcium or iron. Indeed, the number of protons fixes the chemical properties of the atom. On the other hand, for a given chemical element (for example hydrogen) the number of neutrons or electrons can vary. When the number of neutrons varies, we speak of isotope ; when it is the number of electrons that varies, we speak of ion .
An example is better than a long speech! … Let’s take calcium. In its core, there are 20 protons, no more, no less (otherwise it would not be calcium!). But there can be 20, 22, 23, 24 or 26 neutrons. These five configurations of the nucleus (20 protons + 20 neutrons OR 20 protons + 22 neutrons OR etc …) are five calcium isotopes .
Around the nucleus of calcium should gravitate 20 electrons (as much as protons) for there to be electrical neutrality. But calcium easily loses 2 electrons during chemical reactions. Ending with 18 electrons and 20 protons, we say that it is the positive ion of calcium. You may also visit https://differencebetweenz.com/ Difference Betweenz to learn more about such similar terms and objects, which confuses us a lot.