The major force behind the formation of an ionic bond is the electrostatic attractive force that exists between negative and positive ions. It is formed by the transfer of one or more electrons from one atom to another. The atom that donates the electrons becomes positive (cation), and the counterpart atom that receives those electrons becomes negative (anion). The attractive force between two oppositely charged ions or species holds the atoms together in an ionic bond.
In an ionic compound, any ion can attract not only the pairing ion or group, but it can also attract neighboring oppositely charged ions, resulting in strong ionic solids.
Now let us take a look at an example to understand this better. The sodium fluoride (NaF) molecule is a result of ionic bond formation between sodium and fluoride ions. Together with this, you should also try to understand Lewis dot structures. Lewis structure will be discussed in detail later in this chapter.
Lewis Electron-Dot Formulas:Lewis electron-dot formulas are diagrammatic representations of the atoms involved and their valence electrons. The valence electrons are usually represented as dots around the elemental symbol.
Formation of the Ionic Bond in NaF
In the formation of the ionic bond, the sodium atom loses the electron from its 3s subshell, thereby becoming Na+.
On the other hand, the fluorine atom takes the electron that is being lost from the sodium atom to form a (F-) fluoride ion.
These resulting ions are oppositely charged and therefore have electrostatic attractive forces between them, resulting in the formation of the ionic bond.
The attractive energy in an ionic bond can be expressed in terms of Coulombic energy, according to Coulomb's law. Imagine this by considering that the ions are spherical and are separated by particular distances. The attractive energy can be expressed as follows:
Here, k (= 9 x 109 J.m/C2) is a constant, q1 and q2 are the charges, and r is the distance between the nuclei of the two ionic entities involved in the bonding.