What is an ion?
An ion is an atom that has a positive or negative charge.
Due to the gain of an electron or loss of an electron, an atom becomes an ion. Here's a quick review of what an atom is:
An atom has protons (which has positive energy), neutrons (which have no energy), and for every proton, an atom has one **electron**.![https://d2jmvrsizmvf4x.cloudfront.net/EI1N5AHQx2SueeXcmE64_atom_parts.jpg)
The nucleus holds the protons and neutrons together. Since a proton has a positive energy, protons can repel each other. The nucleus tops that. (They're like a magnet. The same sides repel each other.)
Anyways, you can probably see in the picture that there are 4 protons and 4 electrons. :)
----------------- Now, onto the ion part... --------------------------
Since there are an equal amount of protons and electrons, atoms have no charge at all. The negative electrons and positive protons cancel each other out. But if an atom gains or loses an electron, the atom becomes a ion.
Here's some extra info!:
The nucleus is orbited by the atom's electrons in shells (a type of energy levels). Shells are those ring things around the protons and neutrons. The above picture is meant to be an example only and does not show the following fact.
Each shell holds a certain number of electrons in an atom. The first shell (the innermost one) holds 2 electrons. The second shell holds 8 electrons and the third (outermost) shell can hold up to 32 electrons! Mind you, different kind of atoms have a different number of shells.
In the previous paragraph, I told you the number of electrons per shell for the ELEMENT OF SODIUM. Other elements can be different. You can know the number of electrons for an element just by looking at the periodic table.
See the 11 at the top? That part tells you how many electrons an element has. Anyways, back to what we were talkin' about. The outermost shell is called the valence shell. Atoms like to have a "full" valence shell. Atoms with a "not full" valence shell, will give up their electrons on their valence shell, becoming a positively charged cations. Atoms with full valence shells take on more electrons, becoming negatively charged anions .
I know that this answer is AWFULLY long and has extra information. I'm so sorry about that! I just can't stop typing an answer. If you want to read just about ions, read up to the "Here's some extra info!:" part. I hope this helps!