Liaisons ioniques

An ionic bond is a non-covalent attraction that holds two oppositely charged ions together, such as the sodium cation and chloride anion in sodium chloride.

In this case, sodium transfers its single valence electron to chlorine. This electron transfer completes the octet of electrons in each combining atom, making them more stable.

The strength of an ionic bond depends on the environment of the ionic compound.

In the air, the ions remain closely packed in a solid crystal. Because there are no polar molecules to pull the ions apart, the strong attraction between opposite charges keeps the compound stable.

But in water, polar water molecules surround the ions and weaken their attraction. The partial negative charge on oxygen is attracted to sodium ions, while the partial positive charges on hydrogen are attracted to chloride ions. This pulls ions away from the crystal, causing the compound to break apart into its ions.