Characteristics of ionic compounds
1. Physical state
(i)
Electrovalent compounds are generally crystalline in nature.
(ii) These
compounds are generally made from ions which are arranged in a regular way as a
crystal lattice.
(iii) Force
of attraction between the ions is non-directional and extends in all
directions.
(iv) Thus
electrovalent compounds exist as three dimensional solid aggregates.
(v) Normally
each ion is surrounded by a number of oppositely charged ions and this number
is called as coordination number
2. High melting and
boiling point
(i) Due to
strong electrostatic forces of attraction, the ions are held tightly in their
position in the crystal lattice.
3. Electrical
conductivity
(i)
Electrovalent solids do not conduct electricity.
(ii) The
reason is that the ions, on account of electrostatic forces of attraction,
remain intact occupying fixed positions in the crystal lattice.
(iii) The
ions, thus do not move in solid state when electric current is applied.
(iv) When
electrovalent compounds are melted or dissolved in a polar solvent, the ions
become mobile.
(v) They are
attracted towards the respective electrodes and act as carrier of electric
current. Thus, electrovalent compounds in the molten state or in solution
conduct electricity.
4. Solubility of Ionic compound.
(a)
Electrovalent compounds are fairly soluble in polar solvents and insoluble in
non-polar solvents.
(b) The
polar solvents have high values of dielectric constants.
(c) The
solubility of an ionic compound in a polar solvent can also be explained on the
basis of lattice energy and hydration energy.
(d) The
electrovalent compound dissolves in a solvent if the value of solvation energy
is higher than the lattice energy of the electrovalent compound.
(e) These
ions are surrounded by solvent molecules. This process is called solvation.
This process is exothermic.
(f) The
value of solvation energy depends on the relative size of the ions.
(g) Smaller
the ion more of solvation, hence solvation energy will be high.