Short answer
An atom is a unit of an element. An ion is a charged particle: it can be one atom that has gained or lost electrons, or a bonded group of atoms carrying charge. “Atom” names the unit; “ion” describes charge status, so a sodium ion is still a sodium atom in one common sense. 1 2
An atom can become an ion by losing or gaining electrons; some ions consist of several bonded atoms.
On this page
At a glance
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| Question | Atom | Ion |
|---|---|---|
| Net charge | Often neutral when contrasted with ion | Nonzero |
| Number of atoms | One | One or more |
| Example | Neutral sodium atom | Na⁺ or polyatomic nitrate ion |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Atom. The basic unit of a chemical element, consisting of a nucleus and surrounding electrons. 1
Ion. An atom or bonded group of atoms with a net electric charge because its electron count does not balance its protons. 2
Key differences
The number of protons identifies the element. Changing electrons changes electric charge without changing that element. A positive ion has fewer electrons than protons; a negative ion has more. 1 2
How to tell them apart
Look at the chemical notation: Na is commonly a neutral sodium atom, while Na⁺ is a sodium ion. A superscript charge on a group such as NO₃⁻ indicates a polyatomic ion, not one atom. 1 2
Where they overlap
A monatomic ion is an atom with net charge, so the categories are not mutually exclusive. Both participate in chemical reactions, and atoms can cycle between neutral and ionized forms. 1 2
Edge cases
Not every ion is an atom: sulfate and nitrate contain multiple bonded atoms. In compounds, formal or partial charges are not always identical to free, isolated ions. The page uses introductory chemical notation. 1 2
Why the distinction exists
Chemists need to track both elemental identity and electric charge because charge governs attraction, bonding and behavior in solution. 1 2
Common misconceptions
Ion does not mean “different element.” Losing an electron from sodium does not turn it into another element; changing proton count would. 1 2
Examples
A neutral sodium atom loses one electron and becomes Na⁺. A chlorine atom gains one and becomes Cl⁻. 1 2
Sources
Sources checked October 3, 2026.
- OpenStax — Atoms, Isotopes, Ions, and Molecules. Atoms and ions.
- OpenStax — Molecular and Ionic Compounds. Ions and ionic compounds.