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Characteristics and Properties of Ionic Compounds


Ionic bonding occurs when there is a large difference in electronegativity between two atoms. This large difference leads to the loss of an electron from the less electronegative atom and the gain of that electron by the more electronegative atom, resulting in two ions. These oppositely charged ions feel an attraction to each other, and this electrostatic attraction constitutes an ionic bond.

Ionic bonding occurs between a nonmetal, which acts as an electron acceptor, and a metal, which acts as an electron donor. Metals have few valence electrons, whereas nonmetals have closer to eight valence electrons; to easily satisfy the octet rule, the nonmetal will accept an electron donated by the metal. More than one electron can be donated and received in an ionic bond.

Some examples of compounds with ionic bonding include NaCl, KI, MgCl2.

Characteristics and Properties of Ionic Compounds

(i).    Hard and Rigid

        Ionic compounds are hard and rigid.
Reason
         The cations and anions are held together by strong electrostatic force of attraction in ionic compounds. Thus, these are hard and rigid.

(ii).    High Density

        Ionic compounds have usually high density.
Reason:
        Density = mass/volume. The cations and anions are held together by strong electrostatic force of attraction in an ionic compound. The volume of the system, thus, decreases and density increases.

(iii).     High Melting and Boiling Points

        Ionic compounds have high melting and boiling points.
Reason:
         The cations and anions are held together by strong electrostatic force of attraction in an ionic compound. A large amount of energy is needed to overcome these forces to cause breaking down of crystal lattice of ionic compounds.

(iv).    Good Electrical Conductivity

        Ionic compounds are good conductors of electricity in molten ( fused) and aqueous form.
Reason:
         When an ionic compound is fused or dissolved in water, it splits up into cations and anions. When electric current is passed through such solutions, the ions move to oppositely charged electrodes. Thus, these compounds are good conductor of electricity.

(v).    Non - Directional Nature

        Ionic bond is non-directional in nature.
Reason:
    A cation and an anion are considered as charged spheres. These ions have a unilateral form field of forces around them. These ions, thus, attract each other. This electrical charge is responsible for their mutual force of attraction and repulsion. These ions have a uniform field of force around them and hence attract oppositely charged ions from all directions. Hence, ionic bond is non -directional.

(vi).    Solubility

       
Reason:       
The force of attraction between the ions is given by the coulomb's law;
               
Where, D is dielectric constant.
For H2O, D = 80
Since the dielectric constant of water is very high, the forces of attraction between Na+ and Cl
ions in the lattice are decreased and hence the crystal dissociates into its ions. Whereas the non-polar solvents have low dielectric constant and cannot dissociate the ionic solid.
Ionic compounds are soluble in polar solvents such as water.

(vii).    Tendency to have fast reactions

        Aqueous solutions of ionic solids undergo fast reactions.
Reason:
         When an ionic compound is dissolved in water, it splits into its ions. When aqueous solutions of two ionic compounds are mixed together, the oppositely charged ions combine at once to give the product. It is because no force is required to break the bond of reacting molecules.

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