ion

An ion is an atom or molecule that has picked up an electric charge — because it has lost or gained one or more of its tiny electrons. Normally an atom is perfectly balanced: as many negative electrons as positive protons, so it carries no charge overall. Knock an electron loose, or stuff an extra one in, and that balance breaks. The leftover charge is what makes it an ion. Table salt is the everyday proof: each grain is a tidy lattice of sodium ions and chloride ions, locked together by nothing more than their opposite charges.

Which way it goes gives the ion its name. Lose electrons and you have a surplus of positive protons — a positively charged cation (like sodium, Na⁺). Gain electrons and the negatives win — a negatively charged anion (like chloride, Cl⁻). Atoms do this constantly to reach a more comfortable, stable arrangement, and the result is everywhere: it's why salt dissolves, why batteries push current, and why the signals in your own nerves are really ions sloshing across cell membranes.

One thing to keep straight: gaining a negative electron makes an ion more negative, and losing one makes it more positive — which can feel backwards at first. The atom's nucleus, with its protons, never changes during all this; only the lightweight outer electrons come and go. Change the protons instead and you'd have a different element entirely, not just an ion of the same one.