Chemical Bonding and Molecular Structure
3.0 Characteristics of Electrovalent Compounds
3.0 Characteristics of Electrovalent Compounds
Melting and Boiling Point:
Due to the powerful electrostatic force between the ions in a crystal of an electrovalent compound considerable energy is needed to overcome these forces and break down the crystal lattice. Hence such compounds possess high melting and boiling points.
Electrical Conductivity:
When an electrovalent compound is molten or dissolved in a solvent of high dielectric constant e.g., water, the binding forces in the crystal lattice disappear and the component ions become mobile. Under the influence of applied electrical field, the ions get charged and thus act as charge carrier of the current. Hence their melts or solutions conduct electricity.
Solubility:
Ionic compounds are soluble in polar solvents like water because of molecules of the polar solvent interact strongly with the ions of the crystal and the solvation energy is sufficient to overcome the attraction between the ions in the crystal lattice. Dissolution is also favoured by the high dielectric constant of the solvents such as water, since this weakens the inter ionic attractions in the resulting solutions.
Non-polar solvents like benzene and carbon tetrachloride do not solvate the ions as their dielectric constants are low. Ionic compounds are, therefore insoluble in non-polar solvents.
Ionic compounds like sulphates and phosphates of barium and strontium are insoluble in water (because lattice energy is greater than hydration energy). This can be attributed to the high lattice energies of these compounds due to polyvalent nature of both the cation and the anion. In these cases, hydration of ions fails to liberate sufficient energy to offset the lattice energy.
