∞ generated and posted on 2016.11.13 ∞

Atom or molecule that has a positive or negative charge.

A negative charge is the result of having an excess of electrons over protons. A positive charge is a result of having an excess of protons over electrons.

Typically electrons are either gained from or lost to other atoms. That is, atoms that display greater electronegativity have a potential to steal electrons from atoms that possess less electronegativity. Such electron loss (or gain) can be either partial or full, but only the complete loss or gain of an electron, in combination with dissociation of the electron-stealing or -donating atom results in formation of an ion.

As a general rule, ions are unable to pass through lipid bilayers without protein-mediated facilitation, that is, unless a transport protein exists that is capable of moving the ion from one side to the other side of a membrane.