Ionic or Electrovalent Bond

When the electronegativity difference between two combining atoms is LARGE, rather than sharing electrons the less electronegative atom completely TRANSFERS one or more of its valence electrons to the other atom, so that both atoms attain the electronic configuration of their nearest inert (noble) gas. This complete transfer creates a cation and an anion; the two ions are then held together purely by electrostatic attractive force, which is called the ionic bond (or electrovalent bond).

Worked example — potassium chloride. Potassium's electronic configuration is [Ar] 4s¹ (one valence electron); chlorine's is [Ne] 3s² 3p⁵ (seven valence electrons). By losing its one valence electron, potassium attains argon's stable configuration and becomes the unipositive cation K⁺; chlorine accepts that electron to become the uninegative chloride ion Cl⁻, also attaining a stable (argon-like) configuration. The two ions combine to form an ionic crystal, held together by electrostatic attraction. …