Ionic Bond
(a) Chemical bond formed between ions is called ionic bond.
(b) Ionic bonds are formed by loss and gain of e– between two
atoms.
(c) The electrostatic force of attraction developed between
the cation and anion is known as ionic bond. It is also called as electrovalent
bond due to involvement of electrostatic forces of attraction.
(d) Electrovalent bond is not possible between similar atoms.
This type of bonding requires two atoms of different nature. One atom should
have the tendency to lose electron i.e. electropositive in nature and the other
atom should have the tendency to accept electron.
Conditions
for forming ionic bond
1. Low ionisation energy of one atom.
2. High electron affinity of other atom.
3. High Lattice energy of compound formed.
Now
for stable ionic bonding the total energy released should be more than the
energy required.
(a)
Ionization energy:
I
n the formation of ionic bond a metal atom loses electron to form cation. This
process required energy equal to the ionization energy. Lesser the value of
ionization energy, greater is the tendency of the atom to form cation. For
example, alkali metals form cations quite easily because of the low values of
ionization energies.
(b)
Electron affinity: Electron
affinity is the energy released when gaseous atom accepts electron to form a
negative ion. Thus, the value of electron affinity gives the tendency of an
atom to form anion. Now greater the value of electron affinity more is the
tendency of an atom to form anion. For example, halogens having highest
electron affinities within their respective periods to form ionic compounds
with metals very easily.
(c)
Lattice energy: Once the
gaseous ions are formed, the ions of opposite charges come close together and
pack up three dimensionally in a definite geometric pattern to form ionic
crystal.
Lattice
energy
(a) The amount of energy released when free ions combine
together to form one mole of a crystal is called lattice energy (v)
M+ (g)
+ X–(g) à M+X–(S)
(b) Higher the lattice energy greater will be the ease of
formation of the ionic compound.
(c) Factors influencing magnitude of lattice
energy are as follows:
(i)
Size of ions: Smaller
the size of the ions, lesser is the internuclear distance.
Consequently the interionic attraction will be high and
lattice energy will also be large. e.g. NaCl > KCl
(ii)
Charge on ions: Larger the magnitudes of charge on
the ions, greater will be the attractive forces between the ions. Consequently
the lattice energy will be high. e.g. L.E. of MgO > L.E of Na2O
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