The formal definition for an ion is an “atom or group of atoms with one or more positive or negative electric charges” (Encyclopedia Britannica).
To explain the process of atoms forming ions, we must first consider the structure of the atom. In simple terms, at the centre of an atom is the nucleus, containing a certain number of neutrons and protons. The neutrons are, as the name implies, neutral, whilst the protons have a positive charge. Surrounding the nucleus are orbitals, probability regions where electrons (with a negative charge), can freely move. The orbitals are generally depicted as shells i.e. concentric circles surrounding the nucleus. Each shell can fit a certain number of electrons and for an atom to be stable’ it must have a full outer shell. This can be described as having the same electron configuration as the nearest noble gases (group VIII of the periodic table).
In all atoms the number of protons equals to the number of electrons. For an atom to gain a stable electron configuration (i.e. a full outer shell), it has to either lose or gain electrons. All metals have slightly more electrons than their closet noble gas, and thus have to donate their outer shell electrons to exist in a more stable state. On the other side, non metals have fewer electrons than their nearest noble gas and have to receive electrons from other atoms to be stable. Since there is a difference in the number of protons and electrons, there is a net positive charge after the metal atoms donate electrons and a net negative charge after the non-metals receive electrons. Through the processes described above, atoms are formed into simple ions. Metal ions are knows as cations whilst non-metal ions are known as anions.
Another form of ions that can exist are polyatomic ions, which are charged molecules. The atoms within a polyatomic ion are usually very tightly bound together, so the ion does not break up when chemically bonded over the course of many chemical reactions.
– Encyclopedia Britannica
– Foundations of Chemistry- Second Edition
PS. I think the other article copied directly from Wikipedia without editing