Ionic bond

An ionic (or electrovalent) bond forms when one atom transfers one or more valence electrons completely to another atom, and the resulting oppositely-charged ions are then held together purely by electrostatic (coulombic) attraction. In sodium chloride, sodium ($Z=11$, configuration $2,8,1$) has only one electron in its outer shell and readily loses it to reach neon's stable $2,8$ configuration; chlorine ($Z=17$, configuration $2,8,7$) has seven outer electrons and readily gains one to reach argon's stable $2,8,8$ configuration. The transfer converts neutral Na into Na⊕ and neutral Cl into Cl⊖, and the resulting electrostatic attraction between these ions is the ionic bond in Na⊕Cl⊖ (NaCl). The same idea extends to ions of different charge, as in calcium chloride: calcium (configuration $2,8,8,2$) has two valence electrons to lose and transfers one each to two separate chlorine atoms, giving Ca²⊕ plus two Cl⊖ ions, written Ca²⊕(Cl⊖)₂ or CaCl₂. In general, an element with a LOW ionisation entha …