Electrovalent or Ionic Bond
"An ionic
bond is the force of attraction between oppositely charged ions in a
compound."
This type
of Chemical bond was proposed by Kossel (1916). Electrovalent bond is formed by
transference of one or more electrons from the outermost shell of one atom to
the valence shell of other. The atom losing electron becomes positive ion due
to having more proton (having +ve
charge) in the nucleus than electrons in shell. The atom which gains the
electrons becomes –ve ion. Consequently, both the atoms acquire inert gas
configuration.
Consider
formation of NaCl from sodium and chlorine atoms. Sodium atom has one electron
in the outermost shell, while Chlorine has seven electrons in its valence
shell. When these two atoms come close each other, one electron from sodium is
transferred to Chlorine atom.
Factor Affecting Ionic Bonds: -
(i). Low
I.E. Values
Ionization Energy is the minimum amount of energy which is required to eject the electron completely from the outermost shell of neutral gaseous atom so as to form a positive ion. Thus, smaller the I.E., easier is to remove the electron to form cation. Hence ionic bond is readily formed.
Ionization Energy is the minimum amount of energy which is required to eject the electron completely from the outermost shell of neutral gaseous atom so as to form a positive ion. Thus, smaller the I.E., easier is to remove the electron to form cation. Hence ionic bond is readily formed.
(ii). High
E.A. Values
The atom which gains the electron must possess strong tendency to accept the additional electrons. Halogens possess high electron affinity & thus show high tendency for ionic bonding. The elements of oxygen family also exhibit remarkable electron affinity & form ionic compounds but not so readily as halogens.
(iii). High Lattice Energy
The atom which gains the electron must possess strong tendency to accept the additional electrons. Halogens possess high electron affinity & thus show high tendency for ionic bonding. The elements of oxygen family also exhibit remarkable electron affinity & form ionic compounds but not so readily as halogens.
(iii). High Lattice Energy
The lattice energy is defined as the
energy released when one mole of an ionic compound is formed from the gaseous
ions. The higher the value of lattice energy of the resulting ionic compound,
greater will be the ease of its formation.
Characteristics of Electrovalent Compounds
1.
Crystal Structure:
In
solid state of electrovalent compounds anions and cations are arranged in
regular manner called as crystal, in which anions surrounded by definite number
of cations and cations surrounded by definite number of anions.
2.
Physical Nature:
Ionic or electrovalent compounds
are generally hard, and their hardness increases with increasing ionic charge
and decreasing distance between ions.
3.
Solubility:
Positive ion of ionic compound attaches
with negative part of polar solvent and negative ion of ionic compound attach
with positive part of polar solvent, so ionic or electrovalent compounds are
soluble in polar solvents like water and insoluble in non-polar solvents like
benzene, ether, alcohol.
4.
Melting Point and Boiling Point:
Electrovalent
or ionic compounds have high Melting and boiling points because they need large
amount of energy to break strong ionic bonds.
5.
Electrical Conductivity:
Because
of the strong electrostatic forces, the ions in the solid are not free to move
and act as poor conductor of electricity in the solid state. However, in molten
and solution forms electrovalent compounds conduct electricity because ions flow
in molten and solution forms.
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