Sodium atomA metal atom with shells of 2, 8 and 1 electrons.
Chlorine atomA nonmetal atom with shells of 2, 8 and 7 electrons.
Valence electronAn electron in the outermost shell. Sodium has one and loses it.
Electron transferOne electron leaves the sodium atom for the chlorine atom.
Valence shellThe outermost shell. Chlorine's holds seven electrons, with room for one more.
The ions 5
Sodium ion (cation)Sodium after losing one electron. It has a positive charge.
Chloride ion (anion)Chlorine after gaining one electron. It has a negative charge.
Ionic bondThe pull between the positive ion and the negative ion.
Full outer shellEight electrons, an octet. The electron from sodium filled the last place.
Crystal latticeThe solid the ions build. The two kinds alternate along every row.
How this list was compiled: Every name and fact checked on 2026-10-01, a name kept only where two independent sources use it. (1) CK-12 Foundation through LibreTexts Chemistry, Introductory Chemistry 8.6 Ionic Bonding and 8.7 Ionic Crystal Structure, https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introductory_Chemistry_(CK-12)/08%3A_Ionic_and_Metallic_Bonding/8.06%3A_Ionic_Bonding (sodium loses its one valence electron and becomes a cation, chlorine gains one and becomes an anion; one electron passes from sodium to chlorine; the ionic bond is the pull between the sodium ion and the chloride ion; complete octet; equal numbers of the two ions; ionic crystal lattice). (2) Wikipedia, text only: Ionic bonding, https://en.wikipedia.org/wiki/Ionic_bonding, and Sodium chloride, https://en.wikipedia.org/wiki/Sodium_chloride (cations and anions, transfer of electrons, full valence shell, a lattice in which the ions alternate and no separate molecules can be told apart; each ion surrounded by six of the opposite charge; the larger chloride ions and smaller sodium ions). (3) Florida State University, General Chemistry lecture notes, Ionic and Covalent Bonding, https://www.chem.fsu.edu/chemlab/chm1045/bonding.html (ionic bonds form after the electrons transfer; valence electrons are those in the outermost shell; sodium ends with the electron arrangement of neon and chloride with that of argon; octet rule). Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
This is how table salt, NaCl, is held together. Count the dots: each is an electron. Tap a numbered ring to see what a part is called, then open the second view for the ions.
Read the full guide
One electron moves
The sodium atom has a single valence electron in its outer shell. The chlorine atom has seven and room for one more. That one electron is transferred from sodium to chlorine. Sodium is left with the electron arrangement of neon, and chlorine gains that of argon.
Two ions and a bond
Having lost an electron, sodium is a positive ion, a cation. Having gained one, chlorine is a negative ion, an anion, called chloride. Opposite charges attract, and that pull is the ionic bond. In solid salt the ions stack in a crystal lattice.
To label an image of the NaCl crystal: the larger balls are chloride ions and the smaller ones are sodium ions.
Questions and answers
What is an ionic bond?
The electrostatic force that holds oppositely charged ions together in an ionic compound. In sodium chloride it is the attraction of each positive sodium ion for the negative chloride ions next to it.
How does sodium chloride form an ionic bond?
Sodium, a metal, loses its one valence electron and becomes a positive ion. Chlorine, a nonmetal, gains that electron and becomes a negative chloride ion. The two ions attract each other.
Is there a single NaCl molecule in salt?
No. A salt crystal has equal numbers of sodium ions and chloride ions in a lattice, and six ions of the opposite charge surround each ion. No separate molecules can be told apart.
Why is the sodium ion drawn smaller than the chloride ion?
The sodium ion has lost the only electron in its outer shell, so it is drawn with two shells. The chloride ion has three full shells, and in the crystal the chloride ions are the larger ones.